tag:blogger.com,1999:blog-42099217213146607312024-03-17T15:03:40.254+00:00SynapsidaA random wander through the world of mammalsJK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.comBlogger674125tag:blogger.com,1999:blog-4209921721314660731.post-49368106871046664252024-03-17T14:54:00.001+00:002024-03-17T15:03:07.279+00:00Home-grown Shovel Tuskers?<p></p><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody><tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgmxBBg9oVJejFPjYG7j3_2ZPx04oWnY_5fed4oEUZdR2xQLEaU5oawbHcTjNVXHPkfR8AJ3loMxuWLgkJGCh_o7avVKb-4I8LMT9JEiJl5RsD_ScKXRYnwv4dSz4buvlYeGRO9qu_fjAFwPOKU9fds8_Ey4N6Ernz0u2QEvO03i_T6YgEJHfDcDDCDoHQ5/s400/787px-Amebelodon21.jpg" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="304" data-original-width="400" height="243" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgmxBBg9oVJejFPjYG7j3_2ZPx04oWnY_5fed4oEUZdR2xQLEaU5oawbHcTjNVXHPkfR8AJ3loMxuWLgkJGCh_o7avVKb-4I8LMT9JEiJl5RsD_ScKXRYnwv4dSz4buvlYeGRO9qu_fjAFwPOKU9fds8_Ey4N6Ernz0u2QEvO03i_T6YgEJHfDcDDCDoHQ5/s320/787px-Amebelodon21.jpg" width="320" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;"><i>Konobeladon</i></td></tr></tbody></table>Elephants are unique and remarkable animals, looking quite unlike any other creature. They have no close living relatives among other mammals - you have to go back almost to the time of the dinosaurs to find any common ancestor with anything else. As a result, the elephant family is placed within its own order of mammals, a ranking equivalent to that given to such groups as "primates", "rodents", or "bats". With just one family, and only three living species, it isn't quite the smallest mammalian order, but it's very close.<p></p><p>This changes significantly if we choose to include the known extinct species. There are a great many of these, which tend to be large, heavily built creatures with elongated tusks, and, in most cases, features on their skulls that suggest they had a trunk. Indeed, this latter is the source of the official name of the order, the <b>proboscideans</b>. While only the elephant family survives today, at least six others are recognised to have existed in the past, and if we could see members of most of them today they'd be instantly recognisable as, if not actually elephants, at least "elephant-like".<span></span></p><a name='more'></a><p></p><p>The elephant family itself, which includes the mammoths, is not especially old, dating from around 10 million years ago, towards the end of the Miocene epoch. They are generally believed to have <a href="https://doi.org/10.1038%2Fs41598-018-25909-4" target="_blank">descended</a> (together with a second family that died out early at the beginning of the Last Ice Age) from a group of animals called the "tetralophodont gomphotheres". </p><p>The word "gomphothere" translates as "wedge-beast" and refers to the greatly elongated, wedge-like, lower jaw of many gomphothere species, which was typically equipped with a second set of tusks. This was probably used to cut vegetation, with the greatly elongated trunk seen in modern elephants evolving later as an <a href="https://doi.org/10.7554/eLife.90908.1" target="_blank">alternative means</a> of obtaining food.</p><p>The exact classification of the gomphotheres is not yet settled. The seven-family scheme for the proboscideans that I mentioned earlier lists them as just one of those families but this is likely an artificial grouping consisting of animals that are not all that closely related to one another, but just happen to look similar. How, and to what extent, we should divide them up is where the uncertainty comes in.</p><p>Among the most bizarre of the gomphotheres are the <b>shovel-tuskers</b>. These are not the direct ancestors of living elephants, but a side-branch that prospered during the Miocene but that died out at the end of the epoch around 5 million years ago. These days they are commonly split off from the other gomphotheres as <a href="https://doi.org/10.1080/14772019.2016.1208687" target="_blank">their own family</a>, the Amebelodontidae. (Which, if you're keeping count, brings us to eight families of proboscidean in total, and many modern schemes would recognise even more).</p><p>Shovel-tuskers were, to be honest, weird-looking. Granted, if elephants didn't exist today, we'd probably regard those as something that looked like they came out of a fantasy novel but, to modern eyes, shovel-tuskers were even stranger. Like most other gomphotheres, they had that greatly elongated lower jaw and a trunk that was likely shorter than that in living elephants. </p><p>They also, in addition to the regular tusks in the upper jaw, had a second set on the lower one. But these lower tusks were wide and flattened, together forming what looks like a giant spatula. In the early 20th century, when the first fossils of shovel-tuskers were discovered, it was thought that this odd structure was used to scoop up vegetation from shallow rivers, hence the common name. More recent analysis has shown that the tusks were <a href="https://doi.org/10.1016/j.palaeo.2016.06.012" target="_blank">not literally used as shovels</a> but were instead used for things such as scraping the bark off trees. Many older reconstructions of the animals also show them with flap-like flattened trunks that lay on top of the "shovel" but a <a href="https://doi.org/10.1017/S0094837300013932" target="_blank">2016 analysis</a> concluded they were probably more elephant-like than that.</p><p>The first shovel-tusker genus to be scientifically named was the one for which the family is named: <i>Amebelodon</i>, in 1927. This lived for around 4 million years at the end of the Miocene in North America, making it one of the last of the shovel-tuskers to die out. Various species have been assigned to the genus over the decades since, ranging from the relatively primitive <i>A. floridanus</i> to more advanced forms with flatter lower tusks and a more well-developed "shovel". </p><p>In 1990, some of the more advanced forms were <a href="https://doi.org/10.1017/S0022336000019855" target="_blank">distinguished</a> by being given their own subgenus. These forms were more successful than their predecessors, at least in geographic terms, with fossils having been discovered as far afield as Libya. The picture seemed reasonably clear: <i>Amebelodon</i> first evolved in North America in the form of <i>A. floridanus</i>, which evolved into the moderately advanced <i>A. fricki</i>, and then into the various species of the newly named subgenus some of which rapidly left America and headed to Africa via an Asian route.</p><p>In 2014, however, this simple picture became more complicated. In that year, a new species of the advanced subgenus was discovered <a href="https://doi.org/10.1080/02724634.2014.873622" target="_blank">in Greece</a> that was as old as any in North America, calling into question in which direction the animal had migrated. This was considered significant enough to promote the subgenus status, and these species, including the late-surviving African one, now get the new name <i>Konobelodon</i>. To make matters worse, however, there is now <a href="https://www.academia.edu/download/33657052/Wang_et_al_2013_Gomphotheriidae_and_Mammutidae_(Proboscidea_Mammalia)_from_the_Miocene_of_the_Linxia_Basin.pdf" target="_blank">evidence</a> of what appears to be one of the intermediate forms from China that's actually earlier than the equivalent in North America.</p><p>This makes it hard to believe that these animals first appeared on the continent where they were initially discovered. The new picture is therefore that the intermediate form, <i>A. fricki</i>, or some as-yet-unnamed species closely related to it, evolved in China, and evolved into <i>Konobelodon</i> locally before the latter headed into North America - the opposite direction than originally assumed - as well as into Europe and Africa.</p><p>This naturally leaves open the question of what to do with the more primitive forms of <i>Amebelodon</i>, which now seem less likely to be the ancestors of <i>A. fricki</i>, and a recent paper suggests moving them to another new genus, <i>Stenobelodon</i>. Once this is considered separately, they argue that it has little obvious relationship to any of the other known shovel-tuskers from North America and, apart from the presence of the partially flattened lower tusks, resembles regular gomphotheres more than it does anything else. In which case, it could be a case of parallel evolution, having evolved the "shovel" independently by modifying the rounded and pointed lower tusks of a common ancestor.</p><p>If that's true - and it's still highly speculative at this point - the entire family of the shovel-tuskers could need revision. It may look weird, but it could be that the shovel-tusker body form was useful enough that it evolved twice.</p><p><i>[Picture by "<a href="https://en.wikipedia.org/wiki/File:Amebelodon21.jpg" target="_blank">DiBgd</a>", from Wikimedia Commons.]</i></p>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com0tag:blogger.com,1999:blog-4209921721314660731.post-90678589181507336392024-03-10T16:11:00.003+00:002024-03-10T16:11:40.709+00:00Jiggling on the Ecotone<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi0NwItoppWWNQLF1E_oWcjUzcXIWA6uH_PulkTjgHLrp6DIDXxIkW9fj37UjV2xjW-NVlvfhwIRo2mrltoKT5_iSVmH7L3ogo2OU-t2jw8EmdJUdBQmHO53_yrbZBw1_Fv0kBMXUnJ8eYY28exuLsH-XTGVoQo67Z3Yk2d3kSSwM73A1MuwXBsCrgmShMU/s400/Cape_Clawless_Otter_-_Bettys_Bay%20(1).jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="322" data-original-width="400" height="258" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi0NwItoppWWNQLF1E_oWcjUzcXIWA6uH_PulkTjgHLrp6DIDXxIkW9fj37UjV2xjW-NVlvfhwIRo2mrltoKT5_iSVmH7L3ogo2OU-t2jw8EmdJUdBQmHO53_yrbZBw1_Fv0kBMXUnJ8eYY28exuLsH-XTGVoQo67Z3Yk2d3kSSwM73A1MuwXBsCrgmShMU/s320/Cape_Clawless_Otter_-_Bettys_Bay%20(1).jpg" width="320" /></a></div>It might leave a slightly different message if a human did it, but leaving piles of droppings in the territory around your home can be an important signal for many mammal species. Although making such piles visible may help other animals find them, the primary signal is, as one might expect, the smell. And not just the smell of the faeces, of course, but complex chemicals mixed in with it from urine or the secretions of anal scent glands. These can allow an animal with a sense of smell more subtle than our own to glean a lot of useful information about who left the deposit - and why.<p></p><p>In many species, this takes the form, not of solitary deposits, but of <b>latrines</b>. In the zoological sense, this refers to a single location for defecating shared by many animals of the same species. The animals who use the site may belong to a particular pack or herd, all using the same communal site, but they could equally well be rivals or neighbours leaving messages for one another. How the latrines are distributed can give researchers <a href="https://doi.org/10.1007/s00265-020-02895-0" target="_blank">significant clues</a> about what those messages might be.<span></span></p><a name='more'></a><p></p><p>What may be the more obvious pattern is for the animals to space their latrines out along <a href="https://doi.org/10.1006/anbe.2001.1802" target="_blank">the edge</a> of their territory. This is likely serving as a 'keep out' sign, and the fact that animals from two <a href="https://doi.org/10.1017/S0952836901001261" target="_blank">neighbouring territories</a> are using the same site indicates that it is, in some sense, an agreed boundary, perhaps with competitors feeling each other out to see how viable a takeover bid might be. The number of latrines, and the spacing between them along the territorial boundary may be a balance between the effort involved in maintaining them, and the likelihood of a newcomer entering the territory encountering one.</p><p>While such boundary marking is probably the more common purpose of latrines, many are often left deep within the territory, where a random intruder is less likely to encounter them. These likely have a different function and it's worth noting that in species such as badgers that use both patterns, they are <a href="https://doi.org/10.1163/156853993X00074" target="_blank">distinct</a> - that is, latrines are either in the centre of the territory, or on the edge, but rarely in the zone in between. Here, the information being provided may be more complex than "keep out", as the latrines are more likely used by different members of the same social group, perhaps enhancing social bonds or setting out <a href="https://doi.org/10.1016/j.anbehav.2003.10.027" target="_blank">dominance hierarchies</a>. Or, if they are warnings to intruders who have somehow failed to notice the boundary marks, they could be placed in areas of <a href="https://doi.org/10.1080/03949370.2014.905499" target="_blank">particular importance</a> to the territory's owner, such as where it finds its best food.</p><p>Many different kinds of mammal engage in this behaviour, including primates and hoofed animals, but it's particularly well-studied amongst carnivores. Mustelids are no exception, with almost all species having well-developed anal scent glands that can be used to mark even without depositing dung at the same time. (Sea otters lack the glands, spending so little time on land that there would presumably be little point). The use of latrines, however, acts as a visual signal that complements the scent mark and many use it, with the few sociable species, such as European badgers and giant otters, being the most likely to share sites with others of their kind.</p><p>There are, however, a great many species of mustelid and even closely related species within the family may behave differently. A <a href="https://doi.org/10.4404/hystrix-28.2-12264" target="_blank">2017 study</a> seems to have been the first to look specifically at the <b>African clawless otter</b> (<i>Aonyx capensis</i>) and revealed that, like some other otters, they not only rub the ground while they scent mark - which presumably helps spread the scent and may use glands other than the anal ones - but they also do a little dance. At the time, the assumption was that the use of the latrines was a means of demarcating the territories occupied by different "clans" of the otters. Now a <a href="https://doi.org/10.1093/jmammal/gyad118" target="_blank">second study</a>, by different researchers, has taken a closer look.</p><p>I <a href="https://synapsida.blogspot.com/2012/06/weasels-in-warm-rivers-otters-of.html" target="_blank">described</a> this species back when I did a survey of the world's mustelid species. They live throughout most of Sub-Saharan Africa outside of dense jungles and arid deserts and have clawless, webless, fingers that they use for dextrously feeling about in the mud for tasty shellfish. Significantly, while they are not as sociable as, say, European badgers, they have what's been described as a <a href="https://doi.org/10.1111/j.1469-7998.1986.tb03576.x" target="_blank">clan-based</a> social structure, where multiple males jointly defend the same territory. And, as mentioned above, scent-marking is a part of that.</p><p>The researchers mapped the locations of otter latrines at two sites, one at the <a href="https://www.google.co.uk/maps/@-28.9547084,31.7714394,4263m/data=!3m1!1e3?entry=ttu" target="_blank">uMlamlazi Nature Reserve</a> and fish farm and the other at a regular farm a few miles away. They then placed camera traps at three of the latrine sites, to more closely observe what the otters were doing when they visited them.</p><p>The study revealed that, of the 38 latrines identified across both sites, the otters had placed the great majority of them at ecotones. An "ecotone" is a place where one type of local habitat gives way to another. Most frequently that was at the edge of a patch of woodland, where the trees stopped and were replaced by tall grass, reeds, or mudflats. But, in this case, other ecotones regularly used to place droppings included riverbanks and roadsides.</p><p>This suggests, without closely observing their movements, that the otters are placing their latrines at the boundary of their territories. Placing them on riverbanks could suggest that they might also be used to mark areas with the best access to food, given what otters are eating, but that they don't do so very often implies it's not a major consideration if it is - a riverbank could equally well be the boundary of a territory, since the Mlamlazi River is at least 100 metres (330 feet) wide at this point. </p><p>Another factor about the placement of the latrines is that they tended to be in places with limited plant cover. This suggests that the otters want them to be visible, perhaps also in places where the wind might waft the scent around rather than vegetation keeping it concentrated. There's an obvious advantage to doing that if you're scent marking, but it's worth noting that it indicates the otters weren't especially scared of predators coming across the marks, either.</p><p>As for what they were doing at the sites, around a third of the time, visiting otters appeared to just be sniffing the site, as one might expect. But those using the site for its more immediate purpose were also performing what the researchers describe as a "jiggle dance". This involves stomping their hind feet and wiggling their back ends about and its exact function remains unclear. If other otters were watching at the time, this could be seen as a visible adjunct to the marking, showing off as a sign of bravado, but that doesn't seem to be what was happening, so maybe it has something to do with distributing the secretions from the scent glands.</p><p>That the latrines seem to be on the edges of territories - presumably clan territories, given what we know of the social life of this species - may imply that, in this species they are less important as a means of sending signals to others already living in that territory. Having said that, several otters were sharing the same site, leading to "overmarking" where one otter adds to the scent already left by another. This could indicate such things as relative social status and, while there's no specific evidence of it here, a female indicating that she's ready to mate would also seem entirely plausible.</p><p>There's clearly a lot more to be understood about the behaviour here and the exact nature of the clan-based all-male groupings. How the females respond to that is a clear place to start with. But this is a start, and does indicate some differences between these tropical animals and the river otters of Europe and northern Asia. If they're jiggling on the ecotone, they must have a good reason for it...</p><p><i>[Photo by <a href="https://en.wikipedia.org/wiki/File:Cape_Clawless_Otter_-_Bettys_Bay.jpg" target="_blank">Grant Hillebrand</a>, from Wikimedia Commons.]</i></p>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com1tag:blogger.com,1999:blog-4209921721314660731.post-72560031880556199242024-03-03T15:33:00.002+00:002024-03-03T15:33:39.361+00:00The Rhinos of Samos<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgd37ji3UA28aJj66oyuhbuptnys2dF7kPMj4HF95plgD4V2IdjkW6fi9ksIwlnC7rSTXzJgDaKAbqSwRvCNIek0YOf8f10TvMtHhKItXJBES81GqGrd2dbEqlFf4DsvroXFa3iI6LDobdKEue69C15EYGxYx1ehyzrBHupDMBVz6PF0kFgmJiTW7_gi-tB/s400/800px-Chilotherium.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="306" data-original-width="400" height="245" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgd37ji3UA28aJj66oyuhbuptnys2dF7kPMj4HF95plgD4V2IdjkW6fi9ksIwlnC7rSTXzJgDaKAbqSwRvCNIek0YOf8f10TvMtHhKItXJBES81GqGrd2dbEqlFf4DsvroXFa3iI6LDobdKEue69C15EYGxYx1ehyzrBHupDMBVz6PF0kFgmJiTW7_gi-tB/s320/800px-Chilotherium.jpg" width="320" /></a></div>Today, rhinoceroses are rare animals, with three out of the five species on the verge of extinction. Millions of years ago, however, not only were they much more common, but there were many more species, and with greater diversity, than we have today. <p></p><p>How diverse that was depends on how broadly you interpret the word "rhino" when fitting it to formal scientific classifications. Even if we take the narrowest definition, considering only animals descended from the last common ancestor of the living animals, you can still add over two dozen species to the tally, although obviously, they weren't all alive at the same time. Adding in all the "rhinoceratoids" - anything more closely related to a rhino than to any other living animal - obviously gets you a great many more, although many of them didn't look much like the creatures we'd recognise. <span></span></p><a name='more'></a><p></p><p>A more middle-of-the-road view would consider just the animals that scientists, based on an admittedly arbitrary dividing line, place in the official "rhino family", the Rhinocerotidae. This lets us include such creatures as the giant elasmotheres, often assumed to have had a truly gigantic horn. But it also includes the aceratheres, a group whose name literally means "hornless beasts" and which therefore, for the sake of simplicity, are often referred to as <b>hornless rhinos</b>. </p><p>Rhino horns, not being made of bone, don't normally fossilise, so there's inevitably some degree of interpretation here - and it's why I said "often assumed to..." when I mentioned the elasmotheres, since we <a href="https://doi.org/10.15298/rusjtheriol.20.2.06" target="_blank">don't actually know</a> how long their horns really were. But what we can say is that the hornless rhinos lack the <a href="https://www.rhinoresourcecenter.com/pdf_files/129/1295058899.pdf" target="_blank">features</a> on the snout that are associated with the base of the horn in living species, so it seems a safe bet in their case. The group was clearly successful, lasting for around 30 million years, with the last known examples dying out at the end of the Pliocene, not long before the first of the Ice Ages began.</p><p>Rhinos of all kinds, the hornless sort included, were particularly diverse during the Late Miocene. In many places, we find several species apparently living alongside one another at the same time. This is certainly plausible, since black and white rhinos both live in South Africa today, but how true it is in every instance depends a lot on how good we are at identifying species. </p><p>Individual species can be difficult to distinguish from fossils alone, and the majority of sources outside the depths of the technical literature resort to naming fossil animals only by their genus - <i>Triceratops</i>, <i>Smilodon</i>, <i>Archaeopteryx</i>, and so on. For living species, this would be odd, since we'd be describing (say) lions, tigers, leopards, and jaguars as if they were all one thing - <i>Panthera</i>. For many fossil species, however, this can be perfectly reasonable, since only one species has ever been named. But where that isn't so, since the species will be, by definition, extremely similar, there can be disputes as to exactly how many we're talking about.</p><p>A particularly rich Late Miocene fossil site lies on the Greek island of <a href="https://www.google.co.uk/maps/@37.7215439,26.7621293,10z?entry=ttu" target="_blank">Samos</a> in the Aegean, just 1.5 km (one mile) off the coast of the Turkish mainland. Among <a href="https://doi.org/10.1016/j.geobios.2010.08.004" target="_blank">many other animals</a>, the site has been the source of no fewer than four named fossil species of horned rhino. But one could legitimately ask just how distinct those really are. After all, none of them come from exceptionally complete fossils and one could always argue that, for example, apparent differences might be due to some other factor such as the age or sex of the animal, or the exact nature of any damage to the skeleton over the millions of years since it died.</p><p>The first description of mammalian fossils from Samos was published by <a href="https://en.wikipedia.org/wiki/Charles_Immanuel_Forsyth_Major" target="_blank">Charles Forsyth-Major</a> in 1884, when the island was still part of the Ottoman Empire. In 1905 M. Weber described the first hornless rhinos from the site, naming <a href="https://www.rhinoresourcecenter.com/pdf_files/130/1309776565.pdf" target="_blank">two new species</a> of <i>Aceratherium</i>, a genus previously described for fossils in Germany. In 1921, however, by which time the island had been handed over to Greece, Julius Andrée named <a href="https://doi.org/10.1007/BF03190415" target="_blank">two more</a> from the same site, bringing the total to four.</p><p>It has later become apparent that <i>Aceratherium</i> was just a dumping ground for animals that weren't necessarily all that similar beyond being large, hornless, rhinos and in 1975, all four of the Samos species were shifted to <i>Chilotherium</i>, a genus known to also have species native to China, India, Kazakhstan, and Ukraine. But four species seems rather a lot to all have existed in one relatively small locality, so are they all really distinct?</p><p>When a new fossil species is named you naturally have to point to a particular fossil specimen that you think is distinct from previously known species and describe it in detail. If anyone later questions whether it really is different from something else, all they have to do is look at the fossil you used in your description and compare it to the original fossil of whatever other animal they are thinking of. All very simple in theory, but there can be complications.</p><p>The main complication in this specific instance is that all four fossils used to name the Samos hornless rhinos were stored in the Bavarian Palaeontology Museum in Munich. Which was hit by a bomb in World War II, destroying them all.</p><p>So, strictly speaking, we'll never know. Theoretically, each of the fossils could belong to some animal that has never been seen again and all four species could be valid, or they could all be examples of the same thing... or somewhere in between. There is, however, a recognised way to at least reduce the scope of this problem; we take a look at other specimens since assigned to the original species, designate one of those as our new defining sample (technically a "neotype") and use that as a point of comparison instead.</p><p>This has now been done, in a study that <a href="https://10.1080/02724634.2023.2254360" target="_blank">reduced</a> the original four species to two but, at the same time, determined that one of them was distinct enough to be given its own genus, <i>Eochilotherium</i>. Some of the differences between the two include a wider head and a different curve to the forehead, but the most visible are perhaps the teeth at the front of the lower jaw. In <i>Chilotherium</i> proper these are huge tusks projecting forwards, possibly <a href="https://doi.org/10.4202/app.2009.0001" target="_blank">larger</a> in the males, but they are smaller, flatter and less conspicuous in the newly named genus. This is a primitive feature, linking <i>Eochilotherium</i> with hornless rhinos from China, while the other Samos species seems very closely related to one in Ukraine.</p><p>We know that the Samos deposits span a time scale of at least <a href="https://doi.org/10.1007/s00531-003-0353-8" target="_blank">9 to 5 million years ago</a>, but it's not clear exactly where within the rock strata the relevant fossils were found. So it's possible that the two species we are now left with did not, in fact, live at the same time; they could have been at least a couple of million years apart. The more primitive one could have wandered across from China while a second population headed through Kazakhstan and/or India (we have fossils from both countries) to reach Ukraine, and there developed into a more "advanced" form with larger tusks and more complex grinding teeth suitable for heavy grazing. That could have then reached Samos, giving rise to the local species and supplanting the older one that had got there first.</p><p><i>[Photo by "<a href="https://en.wikipedia.org/wiki/File:Chilotherium.jpg" target="_blank">Iaikayiu</a>" from Wikimedia Commons.]</i></p>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com0tag:blogger.com,1999:blog-4209921721314660731.post-12695354130622756112024-02-25T17:04:00.000+00:002024-02-25T17:04:06.518+00:00Antilopine Antelopes: Tommy's Gazelle and Relatives<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody><tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEibevVEKV1XWTXTB21bz6gdF8_PBwJdkdiI5ojB5g9JtJx1t5jKJCLiAp_wCzi5Bgq0TY_RQSeu7hDm-sH_7Gw9Vuov06mNP9noU16kGhnOW-dfbqStPHERnm9MXjsOVGuJAYBIvh5vEvmu358wF_Qogo6EFxwhLn7cgFcmvmV1NkK2Y0OsEAvpouWNwqne/s400/Eudorcas_thomsonii_-Serengeti_National_Park,_Tanzania-8.jpg" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="357" data-original-width="400" height="286" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEibevVEKV1XWTXTB21bz6gdF8_PBwJdkdiI5ojB5g9JtJx1t5jKJCLiAp_wCzi5Bgq0TY_RQSeu7hDm-sH_7Gw9Vuov06mNP9noU16kGhnOW-dfbqStPHERnm9MXjsOVGuJAYBIvh5vEvmu358wF_Qogo6EFxwhLn7cgFcmvmV1NkK2Y0OsEAvpouWNwqne/s320/Eudorcas_thomsonii_-Serengeti_National_Park,_Tanzania-8.jpg" width="320" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">Thomson's gazelle</td></tr></tbody></table>You probably don't need to live in Africa to be aware that there are a great many different kinds of antelope. (A couple of years ago I came across an online picture quiz of "can you name these African animals?" Over half of them were antelopes.) It's hard to say which of these are the most familiar to the general public, because quite a few of them probably are, at least in general terms. But one subtype of antelope that people will at least recognise are the gazelles.<p></p><p>Gazelles are smallish, fleet-footed animals; the word comes from the Arabic <i>ḡhazāl</i>, which literally means something like "slim/agile creature". Gazelles are widespread, perhaps surprisingly so, and there are many different species. Of these, the one that may be the most familiar to people outside of Africa is <b>Thomson's gazelle</b> (<i>Eudorcas thomsonii</i>) for the simple reason that it's the one that lives in the Serengeti and therefore gets into a lot of wildlife documentaries. Mostly getting eaten by big cats, to be sure, but it's a start.<span></span></p><a name='more'></a><p></p><p>In fact, Thomson's gazelle is found only in the Serengeti and neighbouring regions in and around the Great Rift Valley in southern Kenya and northern Tanzania. It was first named in 1884, after <a href="https://en.wikipedia.org/wiki/Joseph_Thomson_(explorer)" target="_blank">Joseph Thomson</a>, who had explored the region for the Royal Geographical Society the previous year. It very much fits the standard image of a gazelle, a slender antelope with a cinnamon-coloured back and white underparts, separated by a wide black stripe beneath a pale buff band along the flanks and clear black-and-white facial markings. The horns are small on the females, but long and with prominent circular bands on the males.</p><p>Thomson's gazelles are grazing animals, with at least 75% of their diet consisting of grass. They will eat other plants, especially in the dry season, but the nature of their diet means that they prefer living in short grasslands and open terrain. The fact that they will avoid, so far as possible, areas with dense vegetation or even especially tall grass makes it easier for them to spot approaching predators but, at the same time, means that they are often far from water, inhabiting parts of the plains that can become parched in the dry season. That this doesn't seem to bother them indicates that they can survive on a relatively minimal water intake, even if they aren't quite desert animals.</p><p>Females live in herds, ranging from two dozen to two hundred individuals, but these don't seem to be very structured as they might be in other herd animals. Instead, adults tend not to interact with one another very much, perhaps staying together more out of convenience than any particular desire to be sociable. While young males tend to live in smaller herds, the older ones maintain individual territories, which vary considerably in size with the local population density, but typically cover 10 to 30 hectares (25 to 75 acres). They patrol the borders of these territories, trying to keep as many females within them as possible, and marking them with scent from the large glands in front of their eyes and with urine and droppings. </p><p>The large groups that the females travel in make this challenging for them - there are only so many individuals that a given male can round up - so the female herds tend to be fairly free-ranging, occupying up to 3 km² (about 1 square mile) each and overlapping the territories of dozens of males. Even then, they are <a href="https://doi.org/10.1111/j.1365-2028.1988.tb00978.x" target="_blank">nomadic</a>, moving <a href="https://doi.org/10.1098/rstb.2017.0013" target="_blank">between</a> grassy plains in the wet season and savannah in the dry season. </p><p>Cheetahs are the most common predators of Thomson's gazelles, although African wild dogs are also a threat and other animals, such as lions, will certainly eat them from time to time. The initial response of the gazelles to detecting a potential predator is, perhaps counterintuitively, to gather to look at it, moving about in slow circles and even <a href="https://doi.org/10.1007/BF00164184" target="_blank">approaching it</a> to take a closer look. While this can be dangerous, it must be beneficial on balance, presumably because it lets the predator know that it has been spotted and that any attack might not be worth its while. </p><p>When placed in danger, younger gazelles will attempt to <a href="https://doi.org/10.1016/S0003-3472(05)80985-6" target="_blank">hide</a>, perhaps by dropping prone in long grass, but adults fast enough to have a chance at outrunning the predator (which may require a decent head start if it's a cheetah) will certainly try to do so. At this point, they will engage in a behaviour common amongst all types of gazelles: pronking or stotting. </p><p>Whichever word you use for it, this involves the animal straightening all four of its legs simultaneously, propelling itself rapidly upwards in a vertical leap. Since this doesn't move them forwards, it actually slows their escape, not allowing them to use their full, and not inconsiderable, speed over flat ground. It also has to be exhausting to do repeatedly, when you'd think the gazelle would rather be using every bit of energy it had to make a run for it. Several reasons have been advanced as to why such a thing would be helpful, including that it might help <a href="https://doi.org/10.1016/j.zool.2018.05.007" target="_blank">warn other gazelles</a> that there's a problem, or that it might be a signal of <a href="https://doi.org/10.1007/BF00299889" target="_blank">physical fitness</a> - telling the predator that it should probably pick a weaker target. But, again, it may just be a very visible way of <a href="https://doi.org/10.1016/S0003-3472(86)80052-5" target="_blank">letting the predator know</a> it has been spotted.</p><p>Like many herbivores, the need to stay vigilant means that they don't require much sleep; they take regular naps throughout the day but for no more than five minutes at a time. Nonetheless, they do spend around half their time resting, sunbathing in the morning and seeking shade in the heat of the afternoon. Although they are more active during the day than at night, they often wander around for an hour or two around midnight before having another lie-down. </p><p>Mating takes place towards the end of the rainy season, so that, with a six-month gestation, birth can take place early in the next one. Like many other herd animals, the mother commonly isolates herself around the time of birth and hides her fawn in long grass, calling out to it when she returns from a feeding trip. This does not, however, appear to be universal, with some mothers <a href="https://doi.org/10.1163/1568539X-00003181" target="_blank">staying with the herd</a> and giving birth in short grass, apparently gaining from safety in numbers as much as they lose from increased visibility. Both methods seem reasonably effective, with the <a href="https://doi.org/10.1163/1568539X-00003181" target="_blank">greatest risk</a> to the fawn coming when it is old enough to leave cover and transition to regular herd living.</p><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: right; margin-left: 1em; text-align: right;"><tbody><tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgvoDmFfKpWsdYMfu6aB2c5mucbqVz6HVTMURXlNHA1PO1D0X8MjQJJnwrBhCh5yx4adTXv9OGzI_G7f-GQszhOZSPbduJN4zV_xCXcZuNXk94-a38frL4GCFdRvFcYyxXyAmb9UsjF91oJ9AOLx6fALRaf7C_1ArlCodln7Xz8tJoS9JLYx-MRBifJBz2h/s400/437px-Gazella_rufifrons_AB.jpg" style="margin-left: auto; margin-right: auto; text-align: center;"><img border="0" data-original-height="400" data-original-width="292" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgvoDmFfKpWsdYMfu6aB2c5mucbqVz6HVTMURXlNHA1PO1D0X8MjQJJnwrBhCh5yx4adTXv9OGzI_G7f-GQszhOZSPbduJN4zV_xCXcZuNXk94-a38frL4GCFdRvFcYyxXyAmb9UsjF91oJ9AOLx6fALRaf7C_1ArlCodln7Xz8tJoS9JLYx-MRBifJBz2h/s320/437px-Gazella_rufifrons_AB.jpg" width="234" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">Red-fronted gazelle</td></tr></tbody></table><p>For much of the twentieth century, Thomson's gazelle was considered to belong to the same genus as most other gazelles, but in 2000 it was split off into its own genus, <i>Eudorcas.</i> This was first named in 1869 for the <b>red-fronted gazelle</b> (<i>Eudorcas rufifrons</i>) but had been subsumed as, at best, a subgenus of other gazelles. It was restored due to some distinctive features that unite Thomson's and red-fronted gazelles but that distinguish them from other species. The most visible of these is the presence of prominent, widely-spaced rings on the horns, but others relate to modifications to the nasal bones that make them less suited to desert environments than most other gazelles.</p><p>Nevertheless, the red-fronted gazelle, like the "Tommies", inhabits parts of the world where rainfall is sparse and seasonal. In its case, this is the Sahel, the great band of semi-desert and scrubby savannah that stretches along the southern edge of the Sahara. Red-fronted gazelles are found from the Sahel's western bound on the Atlantic coast in Senegal right the way across Africa to the banks of the White Nile in Sudan, taking in many other countries along the way. Although they, too, do not need to drink water very often, obtaining enough from the plants they eat, they migrate south in the dry season, heading towards less inhospitable terrain before returning to the edge of the Sahara in the milder wet season.</p><p>They are about the same size as Thomson' gazelles, standing about 75 cm (2' 6") at the shoulder and have a similar build. They are, as their name suggests, a richer red in colour, and the black band along their flanks is not only narrower, but has a second red band just below it, separating it from the white underbelly. </p><p>They are grazing animals, although perhaps less reliant on grass than their relatives. Females live in much smaller groups, perhaps due to the constraints of a relatively harsh habitat where there likely to be less food to go around; fifteen adults per herd is about the maximum, and any more than six is unusual. The males seem to have similar habits to Thomson's gazelle, staking out territories in much the same manner. The clearance of their already marginal native habitat for farmland and livestock grazing means that their population is almost certainly declining, although they remain well short of becoming an "endangered" species.</p><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody><tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiNv7phQl8TkEcPXcGXooIpaWw0AHv1XyBQFVqGl6Tg2teG7HBxph7mZqAxLHdl2syIvr994Z3YKDiaogvfhjrodrLZ-viB1UKQLmVI9bPymEbYKOWMEj3MdlkRbpQHzy22jiUKQCYnzZfoGdre_zE35jnTK_Gc6DnhRPB6XHnqyVFSwEz35_JY7skd2GS3/s400/The_book_of_antelopes_(1894)_Gazella_tilonura.png" style="margin-left: auto; margin-right: auto; text-align: center;"><img border="0" data-original-height="400" data-original-width="368" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiNv7phQl8TkEcPXcGXooIpaWw0AHv1XyBQFVqGl6Tg2teG7HBxph7mZqAxLHdl2syIvr994Z3YKDiaogvfhjrodrLZ-viB1UKQLmVI9bPymEbYKOWMEj3MdlkRbpQHzy22jiUKQCYnzZfoGdre_zE35jnTK_Gc6DnhRPB6XHnqyVFSwEz35_JY7skd2GS3/s320/The_book_of_antelopes_(1894)_Gazella_tilonura.png" width="294" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">Heuglin's gazelle</td></tr></tbody></table><p>There has been some debate over the last couple of decades as to how many species belong within the genus <i>Eudorcas</i>. When it was originally created, there were just two, but more recently there has been a move to split one or both of these further. The most accepted scheme these days leaves Thomson's gazelle as a single species, but splits off the two most easterly subspecies of the red-fronted gazelle into their own species.</p><p>Thus, east of the White Nile in South Sudan, we now find the <b>Mongalla gazelle</b> (<i>Eudorcas albonotata</i>). It has a narrower face than the red-fronted gazelle, with slightly longer horns in the male and much shorter horns in the female. The colour is less obviously reddish, closer to the cinnamon of Thomson's gazelle, and with a broader black stripe than the red-fronted species. Living in floodplains and seasonally watered savannah, it is also said to live in much larger herds.</p><p>Further to the north, also across the Nile, but in Sudan proper, and also across the border into parts of Ethiopia and Eritrea, we instead find <b>Heuglin's gazelle</b> (<i>Eudorcas tilonura</i>) named for the German naturalist who first described it in 1863. Here, the horns of the females are closer in length to those of the males than in the other species, and a narrow black band they all possess stretching vertically across the rump is missing. It's probably the least studied of the four currently accepted species, but is considered endangered, likely restricted to just a few national parks across the region, and with no more than 2,500 adults remaining, if that. It inhabits semi-arid highland plateaus.</p><p>A few sources list a fifth species, the "red gazelle" (<i>E. rufina</i>) which is said to have once lived on the north side of the Sahara in Algeria and to now be extinct. However, there is no evidence that this ever existed. It has never been seen alive, and the pelts it was named from had probably been shipped from elsewhere in Africa - the only one to be genetically tested proved to belong to a regular red-fronted gazelle.</p><p>There are, however, many other species of gazelle in Africa, less closely related to the animal most familiar from all those documentaries filmed in the Serengeti. Next time, I will be taking a look at some of those.</p><p><i>[Photos by "<a href="http://picasaweb.google.com/105399691152412426721" target="_blank">Bob</a>" and <a href="https://pl.wikipedia.org/wiki/Wikipedysta:Chepry" target="_blank">Andrzej Barabasz</a>, from Wikimedia Commons. Drawing by Philip Sclater, in the public domain.]</i></p>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com0tag:blogger.com,1999:blog-4209921721314660731.post-59533818070177348452024-02-18T16:34:00.001+00:002024-02-18T16:34:26.181+00:00Oligocene (Pt 7): Not Quite Camels, Not Quite Pigs<p><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody><tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgW2ZF8OlTupYOPL9JvEEx-oPmsELg8Q1_x1YxUtph7NYINW4yJjRFtotJy6Yusuy8Zd4IaKnoBzShba5VOwdp5B9NS1uZkVXHBZO1UE-h4Q3mY2OCP9qt1ISerW4GNeNcNo3bQIOeZFwGXTVPuNkDENZbmxVts6IrYpdpa74C58yG5emaGiOWFLyIwa9qw/s400/Knight_Protoceras.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="338" data-original-width="400" height="270" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgW2ZF8OlTupYOPL9JvEEx-oPmsELg8Q1_x1YxUtph7NYINW4yJjRFtotJy6Yusuy8Zd4IaKnoBzShba5VOwdp5B9NS1uZkVXHBZO1UE-h4Q3mY2OCP9qt1ISerW4GNeNcNo3bQIOeZFwGXTVPuNkDENZbmxVts6IrYpdpa74C58yG5emaGiOWFLyIwa9qw/s320/Knight_Protoceras.jpg" width="320" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;"><i>Protoceras</i></td></tr></tbody></table>While the ruminants of Oligocene North America would have looked similar to the musk deer of today, some of the other cloven-hoofed mammals inhabiting the continent at the time were more distinctive. <b>Protoceratids</b> no longer survive, but they had already been around for millions of years at the dawn of the Oligocene, and would survive throughout the whole of the following epoch and a little way into the one after that - an impressive record. Despite this, they never seem to have been very common, and the only undoubted Oligocene example is <i>Protoceras</i>, known primarily from Nebraska, Wyoming, and South Dakota.</p><p>It remains unclear exactly what protoceratids were, beyond the fact that they were obviously related to other cloven-hoofed animals. Some features suggest that they were closely related to ruminants (as was assumed when they were first discovered in the 19th century) while others indicate a close relationship to camels; it may even be that they are some early branch that doesn't fit well with either. Despite being the animal for which the group is named, <i>Protoceras</i> is not so well known as its later relatives, many of which notable for possessing a third horn on their snouts in addition to those in the place we'd expect to find horns on a goat or antelope. <span></span></p><a name='more'></a><p></p><p><i>Protoceras</i>, however, was relatively primitive and had yet to develop this unusual third horn. Instead, while females seem just to have two small, regular horns, the males not only had larger ones but two extra pairs on the snout for a full set of six horns in total, plus a pair of fang-like teeth in the upper jaw. They otherwise had a similar shape and size to roe deer, being something like 1 metre (3 feet) in body length and plausibly had a similar diet; their low numbers may be due to them relying on limited patches of riverside forest for their food. Analysis of the bones in their ears that would have held their organs of balance suggest that <a href="https://doi.org/10.1371/journal.pone.0251832" target="_blank">they were as agile</a> as many antelopes if not quite up to the standards of, say, a gazelle.</p><p><b>Peccaries</b> had first entered North America towards the end of the previous epoch, but were still not particularly diverse, with only two genera clearly identified from the Oligocene (although some fossils are hard to place, so there were likely more). The earlier of the two was <i>Perchoerus</i>, a genus sufficiently primitive that it has been argued that it may be an <a href="https://doi.org/10.1080/14772019.2012.704409" target="_blank">early side-branch</a> of the pig-peccary ancestral stock rather than a true peccary - although this does not appear to be the current consensus. Whatever it was, the larger of the two Oligocene species of <i>Perchoerus</i> was about the size of a modern peccary, and was joined towards the end of the epoch by <i>Thinohyus</i>, which was notably larger with larger teeth and a comparatively elongated head.</p><p>If neither peccaries nor protoceratids were especially common or varied, the same was not true of the <b>oreodonts</b>. Today, these are generally considered to be more closely related to camels than to true ruminants, although the relationship probably isn't very close, and most of them certainly didn't look at all camel-like. Instead, most would have looked somewhat like pigs, with squat bodies and stocky limbs and without any horns or other adornments. Fossil oreodonts are common across much of North America, being best known from the same extensive White River fossil beds as <i>Protoceras</i>, but also found across the western US and as far afield as <a href="https://doi.org/10.1206/0003-0090(2003)279%3C0368:C%3E2.0.CO;2" target="_blank">Florida</a>, <a href="https://doi.org/10.1016/j.jsames.2019.102388" target="_blank">Mexico</a>, and Central America.</p><p>This wide distribution suggests that at least some of the species were highly adaptable, able to eat a wide range of plants across many different habitats. The exact number of known species is debatable; it's generally recognised today that many of those named in the mid 20th century aren't "real" in the sense of being genuinely different from one another, but there are so many that it would be a major undertaking to sort it all out.</p><p>In the early Oligocene, the most common examples were <i>Merycoidodon</i> and <i>Miniochoerus</i>, both of which seem to have been present in large numbers. (Indeed, the technical name for oreodonts is "merycoidodontoids" due to some confusion over the original name). The former was about the size of a pig, and the latter somewhat smaller, but both were relatively <a href="https://www.google.co.uk/books/edition/FOSSIL_RECORD_8/YCKIEAAAQBAJ?hl=en&gbpv=1&dq=merycoidodon&pg=PA447&printsec=frontcover" target="_blank">unspecialised</a> herbivorous animals with a full set of teeth in the upper jaw and biting canines. Notably, while they had the general cloven-footed pattern to their feet, they still walked on four toes on each foot. From around the middle of the epoch, they began to diversify, with a <a href="https://doi.org/10.1007/s10914-005-9001-3" target="_blank">general trend</a> to a diet of tougher food, perhaps switching from forest fruits to soft-leaved browse as a primary food source, and later still to a mixed browsing-grazing lifestyle. </p><p>These later forms include <i>Merycochoerus</i>, which has a physique that may indicate that it spent a lot of time wading in swamps or swimming in rivers, and the physically large but short-snouted <i>Eporeodon</i>. One of the more abundant examples from this later time is <i><a href="https://www.google.co.uk/books/edition/Neogene_Mammals/vW_aBwAAQBAJ?hl=en&gbpv=1&dq=leptauchenia&pg=PA335&printsec=frontcover" target="_blank">Leptauchenia</a></i>, notable for teeth adapted to chewing tough plants, large inner ear cavities, and eyes placed unusually high on the head. Deep pits in the skull in front of the eyes most likely held large scent glands, similar to those in some modern animals such as gazelles. The high position of the eyes was once used to argue that they may have been semi-aquatic, peeking up above the water surface like a hippo, but the geology of the fossil beds they are found in suggests that they lived in <a href="https://www.google.co.uk/books/edition/Neogene_Mammals/vW_aBwAAQBAJ?hl=en&gbpv=1&dq=leptauchenia&pg=PA335&printsec=frontcover" target="_blank">arid habitats</a> dominated by wind-blown sand.</p><p>While many later oreodonts were larger than the earlier forms, reaching the size of a large sheep, a later relative of <i>Leptauchenia</i> went in the opposite direction. Otherwise looking similar to its relative and likely living in similar environments, <i><a href="https://digitalcollections.sdsu.edu/do/1bd8a7d4-4826-4d77-9e96-c35a4f6846dc/file/5fb3fee3-1306-4cb0-bf60-b6d27d67b7a5/download/matsuoka_2014.pdf" target="_blank">Sespia</a></i>, known from western Nebraska to the California coast, was about the size of a house cat.</p><p><i><a href="https://doi.org/10.1080/02724634.2015.1041970" target="_blank">Agriochoerus</a></i> was closely related to the main oreodont family, and sometimes placed within it, but it's generally considered to have been weird enough to get a family of its own (and whether that still leaves as an 'oreodont' or just something similar is a matter of the precise definition). In many respects, it resembled the oreodonts proper, being similarly sized, having the full set of teeth, including the sharp canines, and walking on four toes on each foot, rather than two. But it had a shape closer to those of their assumed common ancestor, with a slender body and a long tail. </p><p>More strangely, however, the hooves on its feet had sharp points and were shaped in such a way that it's hard to describe them as anything other than "claws". Since this is still a cloven-footed mammal we're talking about, and every other indication is that it was herbivorous, there has naturally been some debate as to what the purpose of these claws was and why the animal was, broadly speaking, shaped like a cat. Some early proposals suggested that it may have used the claws to dig burrows in the ground, but this is now thought unlikely, and the best bet remains the original one from the 19th century when it was discovered - that this was a cloven-footed herbivore that climbed trees.</p><p>It probably wasn't great at climbing, being the size of a large pig and completely lacking opposable thumbs, but perhaps it didn't need to be. It was, after all, still smaller than a leopard, let alone a bear, and those are capable of climbing. One unpublished analysis apparently compared the limb proportions of <i>Agriochoerus</i> to those of the herbivorous and equally implausible-sounding tree kangaroos, which are an actual thing that exists today, so perhaps those would work as an analogy.</p><p>All of the above groups were unique to North America, but the remaining group of Oligocene cloven-hoofed animals on the continent was also present in Europe and Asia at the time. The entelodonts, informally known as <b>hell-pigs</b>, were represented in Oligocene North America by <i>Archaeotherium</i>, a long-legged but heavily built animal standing around 1.2 metres (4 feet) high at the shoulder and likely weighing at least 280 kg (620 lbs). Despite the name, which comes from a superficial resemblance and older classification systems, they were probably closer to hippos than to pigs. </p><p>Like other hell-pigs, <i>Archaeotherium</i> had a massive head with long powerful jaws and an array of powerful teeth that suggest it was an omnivore that often fed on tough food. While it lacked the sharp slicing teeth of true carnivores, this almost certainly included scavenging on carcasses. Fossils of smaller mammals such as <i>Merycoidodon</i> and the camel <i>Poeboetherium</i> have been found with tooth marks interpreted to have been caused by hell-pigs, and that might even suggest limited active predation. The skull also has large bony flanges and lumps, somewhat reminiscent of those of warthogs, and likely used in the same manner, in combat between males - again, there are scratch marks on some of their skulls that support this interpretation.</p><p>The hell-pigs died out in Eurasia towards the end of the Oligocene, but in North America, <i>Archaeotherium</i> was instead <a href="https://www.nps.gov/subjects/fossils/upload/5th_conf_NPSG_999_D1326_id136637_web.pdf" target="_blank">replaced</a> by the even larger, rhino-sized, <i>Daeodon</i> although whether that was the result of a last-gasp migration from Asia or a direct descendant of its predecessor is unclear. That survived into the following, Miocene, epoch before it too died out bringing the lineage of the hell-pigs to an end.</p><p>However, not all large mammalian herbivores in Oligocene North America were cloven-hoofed and next time I will be looking at some of the others...</p><p><i>[Painting by Charles R. Knight, in the public domain.]</i></p>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com0tag:blogger.com,1999:blog-4209921721314660731.post-89443904737195797752024-02-11T17:01:00.005+00:002024-02-11T17:01:58.331+00:00A Tiger's Dinner<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhZlJBEs8QL6ASQtBeHrLjqXCtktfpNIQK1Jj5X4Uru_CEJXrINKTI3MYm4dhDCLEvKKMV7MrtDpMkAzNb1Ej4MnJRHATnE0CRxj9boKJqDfIZG7FnOzZ4GtIqIq2dgv7b0KkT1o2JcBxJmy6bvu5jj808_eQW51RONOuPkiQUnshHqmZdcHi0Zsy5Ap3pM/s400/Adult_male_Royal_Bengal_tiger.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="259" data-original-width="400" height="207" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhZlJBEs8QL6ASQtBeHrLjqXCtktfpNIQK1Jj5X4Uru_CEJXrINKTI3MYm4dhDCLEvKKMV7MrtDpMkAzNb1Ej4MnJRHATnE0CRxj9boKJqDfIZG7FnOzZ4GtIqIq2dgv7b0KkT1o2JcBxJmy6bvu5jj808_eQW51RONOuPkiQUnshHqmZdcHi0Zsy5Ap3pM/s320/Adult_male_Royal_Bengal_tiger.jpg" width="320" /></a></div>One of the basic concepts in ecology is that of the food chain; the idea that plants are eaten by herbivores are eaten by small carnivores are eaten by large carnivores. The reality is both more complex - because, for example, omnivores exist - and simpler, because, at least on land, many of the largest carnivores eat large herbivores, not smaller carnivores. Nonetheless, there's still an underlying truth, and it introduces us to concepts such as the apex predator.<p></p><p>An apex predator is essentially a carnivore that has no predators of its own, an animal that sits at the top of its local food chain. Many mammals fit this description, including wolves, big cats, bears, and killer whales. (The last of those, of course, being an example of a large carnivore that <i>does</i> mainly eat smaller carnivores). Outside the world of mammals, one could add eagles, crocodiles, and sharks, among others. Humans could count as <a href="https://doi.org/10.1073%2Fpnas.1323645111" target="_blank">another example</a>, given that we obviously don't have regular predators, but this does <a href="https://doi.org/10.1073%2Fpnas.1305827110" target="_blank">depend</a> on your exact definition, since we're clearly omnivorous and, in many parts of the world have a nearly or totally herbivorous diet.<span></span></p><a name='more'></a><p></p><p>A key feature of apex predators is that they are rare. Since an animal cannot convert its food into energy with 100% efficiency there is less energy available to support herbivores than there is to support plants, and less energy for carnivores than there is for herbivores. And so on up the chain. You can't have an ecosystem where everything's big and scary; predators have to eat something, and whatever it is has to be more numerous than they are. On top of that, the reality is that humans <a href="https://doi.org/10.1017/S003060530899030X" target="_blank">don't really like</a> apex predators - at least, not wild ones living close to where they are.</p><p>The <b>tiger</b> (<i>Panthera tigris</i>) is a clear example of this. Tigers are among the most iconic mammalian apex predators, and for all that we admire their beauty and grace, most people probably wouldn't want one prowling the countryside near where they live. The fact that tigers happily eat our livestock given the opportunity and, on occasion, will attack and kill humans has led to <a href="https://doi.org/10.1111/j.1749-4877.2010.00218.x" target="_blank">conflict</a> between them and ourselves, and it's a fight that, in the long run, the tigers aren't winning.</p><p>Tigers used to live from eastern Turkey to the Pacific coast, but no longer. They have vanished entirely from western and central Asia, as well as from Pakistan, Korea, Vietnam, Cambodia, and the islands of Java and Bali. Although estimates vary, it's thought that there are not much more than 3,000 adult tigers left alive in the world, about <a href="https://doi.org/10.1002/pan3.10177" target="_blank">80%</a> of them in India. Unsurprisingly, they are officially listed as an endangered species, and most of those in India are found in legally protected areas. </p><p>But still, around a third of them are not, and even the protected areas <a href="https://doi.org/10.11609/jott.3015.10.7.11844-11849" target="_blank">aren't always</a> as safe as they are supposed to be.</p><p>Since so much of the conflict between tigers and humans is driven by the predators eating livestock, an understanding of the diet of tigers across different areas would clearly be beneficial, and many such studies exist. But how exactly to do this, given the difficulty of following the tigers about and watching them all day? As an illustration, we can look at one <a href="https://doi.org/10.1093/jmammal/gyad069" target="_blank">recently published</a> study, surveying tigers in part of northern India between 2014 and 2020. </p><p>This was a wide-ranging study, looking at tigers in an area called the Terai Arc Landscape which stretches for about 900 km (560 miles) along the foothills and lowlands (<i>terai</i> is Sanskrit for "lowlands") on the southern side of the Himalayas in northern India and southern Nepal. With a total area of about 15,000 km² (5,800 square miles), this encompasses eight wildlife sanctuaries and national parks on the Indian side of the border, where the study was conducted. It's a diverse area, ranging from high foothills to lowland forests, grassland, and swamps.</p><p>Despite its high human population density, it's an area rich in wildlife, with predators including leopards, hyenas, wild dogs, and (omnivorous) bears in addition to tigers. It is also home to rhinos and wild elephants as well as the endangered hispid hare, and birds such as the near-extinct Bengal florican (a type of bustard). Still, the tigers are probably the most famous wild residents, with the region being home to around 650 of the animals - which you'll note is somewhere around a fifth of the worldwide population.</p><p>To see what the tigers had been eating, the researchers followed animal trails at multiple different locations across the landscape, including both protected areas and unprotected forests. Rather than observing the tigers directly, they brought along wax bags and placed any large carnivore droppings they found inside them to take back to a laboratory. </p><p>In total, over the six years of the study they collected 1,689 dung samples. However, one large carnivore dropping looks much like another, so the first thing they did with them was to <a href="https://doi.org/10.1007/s10592-007-9289-z" target="_blank">test</a> them for the presence of tiger mitochondrial DNA. That left them with 525 samples that definitely came from tigers, which they dried out and sieved to obtain undigested bits of hair that they could check under a microscope to try and identify the prey species. (<a href="https://doi.org/10.1002/edn3.27" target="_blank">Genetic analysis</a> would likely have helped here, but seems to have been beyond the budget of the study and the researchers argue that tiger diet isn't varied enough for this to be an issue).</p><p>It's no great surprise that the study found that the great majority of what the tigers were eating were various large-bodied herbivores, with deer as the most common prey item. In the foothills, <a href="https://synapsida.blogspot.com/2021/03/all-worlds-deer-sambar-and-rusa.html" target="_blank">sambar</a> were the favoured prey, a species of deer about the size of a red deer or elk, and thus almost as large as deer get. In the lowlands, where sambar are less common, they switched to the smaller <a href="https://synapsida.blogspot.com/2021/04/all-worlds-deer-deer-with-spots.html" target="_blank">chital</a> deer but there's a suggestion that they didn't really consider these a filling meal, eating them only because they were so common. Instead, when they could, tigers in the lowlands were eating a much higher proportion of livestock than those in the foothills, apparently seeking out oxen and the like when their preferred larger prey were not available.</p><p>So how does this help us? For one thing, the pattern of locations in which the researchers found tiger droppings shows that they are by no means only restricted to the tiger reserves and other protected areas. They can and do wander across the landscape more widely, into places where they are neither protected from attacks, nor monitored to assess their population. Furthermore, it allows us to highlight areas where tigers are eating livestock, putting them at the <a href="https://doi.org/10.1371/journal.pone.0195612" target="_blank">greatest risk</a> of retaliation by local farmers.</p><p>Significantly, tigers in lowland protected areas, where there shouldn't be many livestock were, in fact, eating just as many agricultural animals as those elsewhere. This may be due to local farming practices, which tend to allow animals to graze freely, perhaps even escaping and becoming feral. In other parts of the world, changes in animal husbandry and paying <a href="https://doi.org/10.1038/s41598-021-84119-7" target="_blank">compensation</a> to farmers can be effective as means to <a href="https://doi.org/10.1016/0006-3207(92)91111-5" target="_blank">reduce conflict</a> between humans and wild predators, and to reduce the risk of <a href="https://doi.org/10.1111/1365-2664.13937" target="_blank">disease</a> spreading from livestock into the wild.</p><p>Knowing where the tigers are most frequently eating domestic animals is a good place to start when it comes to focussing our conservation efforts.</p><p><i>[Photo by "<a href="https://en.wikipedia.org/wiki/File:Adult_male_Royal_Bengal_tiger.jpg" target="_blank">Seemaleena</a>", from Wikimedia Commons.]</i></p>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com5tag:blogger.com,1999:blog-4209921721314660731.post-56408181093960182622024-02-04T17:11:00.001+00:002024-02-04T17:11:30.074+00:00Playing Squirrels<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgFVxUYBuXcZWvzwWPeJWTeFrWWOQvWv3hnajhAov9uKWSIn1t_u1xWUIDkf-ckKAFgJepGNFEZ2Hia0nFU62oqWRymVF80IaOa8ojVeEPh5jkp3JR3PsIAx2JoJZ4btqBkxq9m169qutZr1tfnM0WDNVG2izMffMbYA_45eFKboEyIoUryToz1_TRGFf4k/s400/Belding's_Ground_Squirrels_DSC0977vv.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="342" data-original-width="400" height="274" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgFVxUYBuXcZWvzwWPeJWTeFrWWOQvWv3hnajhAov9uKWSIn1t_u1xWUIDkf-ckKAFgJepGNFEZ2Hia0nFU62oqWRymVF80IaOa8ojVeEPh5jkp3JR3PsIAx2JoJZ4btqBkxq9m169qutZr1tfnM0WDNVG2izMffMbYA_45eFKboEyIoUryToz1_TRGFf4k/s320/Belding's_Ground_Squirrels_DSC0977vv.jpg" width="320" /></a></div>Anyone who has owned a cat or dog will know that <b>playing</b> with toys is not something unique to our own species. Indeed, playing in general is a widespread phenomenon among mammals, and <a href="https://doi.org/10.1007/s10164-009-0167-7" target="_blank">less commonly</a>, in other animals, too. (<a href="https://doi.org/10.12966/abc.02.04.2015" target="_blank">Crocodiles and alligators</a>, to take just one example). It's perhaps not as thoroughly studied as some other aspects of mammalian behaviour, but it has by no means been ignored and can be useful, for instance, to enrich the lives of animals kept in zoos.<p></p><p>In order to study play in animals, however, we first need a clear definition of exactly what it is we're talking about. A common model used today is the one defined by Gordon Burghardt in a <a href="https://books.google.co.uk/books?hl=en&lr=&id=kWR6AgAAQBAJ&oi=fnd&pg=PR9&dq=animal+play+behavior&ots=HUko5etxj9&sig=NaJ5il6xdIzPsLFEDFMyy8KXjJ0" target="_blank">2005 book</a> on the subject, which defines play as a physical activity meeting four key criteria.<span></span></p><a name='more'></a><p></p><p>Firstly, the behaviour has to be something that the animal does of its own volition; it has to be something that the animal <i>wants</i> to do and isn't being forced into. Secondly, and in a similar vein, it has to be performed by healthy, unstressed individuals, rather than something it only does when (say) trapped in a bare and empty cage for days on end. Thirdly, it has to be something that the species in question performs frequently, not some one-off reaction to an unusual situation - although there's no requirement that all members of a species should play in exactly the same way. </p><p>Finally, there has to be no obvious point to it. Play does not achieve anything concrete, either because it doesn't resemble other activities, or because, if it does, it doesn't produce the same results. For instance, a cat might play with a toy as if it were a mouse, but it's clear that it doesn't expect to get an actual edible mouse out of this once it's finished.</p><p>So why bother? One could argue that it's just a side-effect of necessary instincts - that a cat plays with a mouse toy because that's just what it does with things that are mouse-shaped. Under this argument, evolution hasn't gotten rid of play activity because, even if it isn't beneficial, there's no real downside to it, either. But it's debatable how true that really is. Playing takes up energy that could be used in looking for food or, for that matter, just relaxing so as to divert scarce resources to bodily growth. It's also potentially dangerous, in that a predator might sneak up on you while you're distracted by playing with a leaf or whatever. </p><p>So the benefits must outweigh those costs or evolution would scrap the activity and let animals focus on something more useful. There have been several studies to try and identify what those benefits might be, and the findings are, perhaps, largely what you might expect. Play is more common in young animals than adults and it's likely that it promotes <a href="https://doi.org/10.12966/abc.05.03.2014" target="_blank">motor or social skills</a> that may be useful later in life. For example, if you <a href="https://doi.org/10.3758/s13420-017-0264-3" target="_blank">play at fighting</a> as a juvenile, you'll probably be better at the real thing when it matters, both physically and psychologically. One study, for instance, found that <a href="https://doi.org/10.1016/j.anbehav.2008.07.009" target="_blank">wild horses</a> were more likely to survive to adulthood and be physically fitter if they had more opportunities to play when they were foals.</p><p>It has also been proposed that play helps develop an animal's temperament - what we'd more likely call 'personality' in humans. The argument here is that it refines a young animal's responses so that it is better able to react appropriately to <a href="https://www.jstor.org/stable/2664002" target="_blank">unexpected situations</a> as an adult. In this sense, we can define at least <a href="https://doi.org/10.1111/j.1469-185X.2007.00010.x" target="_blank">three ways</a> in which personality might vary among animals. Loosely speaking, we can describe these as bravery, curiosity, and sociability. Depending on the exact circumstance, <a href="https://doi.org/10.1098/rspb.2004.2680" target="_blank">different levels</a> of each of these three traits may be <a href="https://doi.org/10.1111/eth.12516" target="_blank">beneficial</a>. For instance, bravery may be helpful <a href="https://doi.org/10.1002/ece3.2886" target="_blank">sometimes</a>, but caution and <a href="https://doi.org/10.1016/j.anbehav.2016.03.026" target="_blank">shyness</a> more so at others.</p><p><b>Belding's ground squirrel</b> (<i>Urocitellus beldingi</i>) is common in and around the Great Basin of the western US. They live in inland grassy regions of California and Oregon, in southern Idaho, northern Nevada, and a small corner of northwestern Utah. They spend about nine months of each year hibernating, mating soon after they wake and giving birth 25 days later. The young emerge from the mother's burrow at around four weeks old and spend the first few hours of each morning in rough-and-tumble play with one another before exploring the outside world. Most of this play activity takes place during their first week above ground, tailing off in the second week as they begin to travel further afield, and essentially stops after that.</p><p>A study in 2017 showed that the baby squirrels which played the most during these two weeks were <a href="https://doi.org/10.1093/jmammal/gyx049" target="_blank">bolder and more curious</a> in unfamiliar but apparently safe environments, spending more time exploring and thus finding it easier to escape from a test site and return home. This is, however, not the same dimension on the temperament scale as bravery/shyness, which is a measure of how they react in the face of a potential threat. So a new study decided to expand on the previous work by measuring how <a href="https://doi.org/10.1093/jmammal/gyad082" target="_blank">easily frightened</a> the young squirrels were.</p><p>Obviously, we don't want to actually put baby squirrels in danger (or no more danger than that posed by the real world of nature). So, instead, the researchers measured the squirrels' bravery by simply walking up to them while they were playing. The question being: how close did they have to get before the squirrels would run away?</p><p>The result was broadly consistent with the previous one; the young squirrels that played the most in the mornings were the most likely to run away when approached by a potentially hostile human. This apparently wasn't the case on the first couple of days after they emerged from the burrows, which the researchers suggest means that it's not an innate aspect of their personality - that is, that the most nervous squirrels are the ones who play the most with their fellows. Similarly, it wasn't that they were any better at spotting intruders, since they started perking up and paying attention at about the same distance regardless, they just let the human get closer before making a run for it.</p><p>Either the act of engaging in social play rewires their young brains to make them more cautious around humans (and presumably other animals) or there's some third factor that makes them both play more and become cautious. For example, their life experiences while exploring in the afternoon might affect how they react both to situations and to each other the following morning. The study also showed that squirrels born to first-time mothers were more cautious than those with older mothers, perhaps due to the <a href="https://doi.org/10.1038/srep27509" target="_blank">quality of the parental care</a> they had received before leaving the burrow for the first time.</p><p>There is some evidence that play in young mammals <a href="https://psycnet.apa.org/doi/10.1037/bne0000148" target="_blank">reshapes</a> the neural pathways in their brain, much as other experiences might, and this can enable them to make better judgements when they respond to new situations as they age. In this case, it seems that social play both makes the squirrels more curious and willing to explore the outside world and tempers that with an understandable caution about the potential risks they might face as a result. </p><p>Regardless of whether it's the ultimate cause of this behaviour or there's something else that happens first, playing in these squirrels is helping them learn to develop a very sensible attitude to the world around them.</p><p><i>[Photo by <a href="https://commons.wikimedia.org/wiki/User:VJAnderson" target="_blank">V.J. Anderson</a>, from Wikimedia Commons.]</i></p>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com0tag:blogger.com,1999:blog-4209921721314660731.post-8648202069082928182024-01-27T16:55:00.001+00:002024-01-27T16:56:07.170+00:00No Such Thing as an Antelope<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh89BsNR88niGFX91bHV0bZ5Z2N0qQs7PfufR3ZiiZEGpuBXFPbJSN7WcasuO15hXnbNLQ3qv3ZeKy2BIh-lSk1ncE3Gl47Wh_DK9vo67xeoavx8LkHnnxEFH2pIxWJptqqElPSl_OP-oLBSGYik3QfsPKQqyGN4OUPmHjfmIrjjr0ovhAZNmgjEV8DnjTt/s400/Gazella_thomsonii_Thomsons_Gazelle_in_Tanzania_3446_cropped_Nevit.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="400" data-original-width="300" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh89BsNR88niGFX91bHV0bZ5Z2N0qQs7PfufR3ZiiZEGpuBXFPbJSN7WcasuO15hXnbNLQ3qv3ZeKy2BIh-lSk1ncE3Gl47Wh_DK9vo67xeoavx8LkHnnxEFH2pIxWJptqqElPSl_OP-oLBSGYik3QfsPKQqyGN4OUPmHjfmIrjjr0ovhAZNmgjEV8DnjTt/s320/Gazella_thomsonii_Thomsons_Gazelle_in_Tanzania_3446_cropped_Nevit.jpg" width="240" /></a></div>There is no such thing as an <b>antelope</b>.<p></p><p>Or at least that's true in the same sense that there's "<a href="https://www.nosuchthingasafish.com/" target="_blank">no such thing as a fish</a>". Which is to say that, obviously, antelopes exist but they aren't a scientifically definable group of animals. Or that, if they were, that group wouldn't map closely to what the regular English word "antelope" is supposed to mean.</p><p>The word entered English during the Rennaissance, and descends, via Latin, from the Greek "ανθολοψ". That first appears in the 4th century (so not old enough to be Ancient Greek, as such) and referred at the time to a mythical beast said to live along the Euphrates that had horns so sharp and serrated that it used them to cut down trees. We don't know why the Byzantine Greeks called it this, but there's not some "lope" that it's "ante" to (nor, to use most other European languages, is it an anti-lope); it's just a coincidence that the word sounds that way. For all we know, they were borrowing a word from some other, older language spoken somewhere out east.<span></span></p><a name='more'></a><p></p><p>It's entirely plausible that the description of the mythic animal was the result of tall travellers' tales referring to an actual antelope of some kind, but that's as much a mystery as the ultimate etymology. In any event, it was only around the 17th century that the word came to be used in English for a real-world creature. </p><p>A century or so later, the first catalogue of scientific names, in 1758, lists five species that we would now consider to be antelopes. While some people describe antelopes as "deer-like", Linnaeus, when he compiled the catalogue, was already aware that they were quite a different sort of creature. This was in part because they had horns, not antlers, and, as I've <a href="https://synapsida.blogspot.com/2013/01/goats-horns-and-antlers.html" target="_blank">previously described</a>, the two types of structure are anatomically distinct. Also recognising that they were neither sheep nor cows, he placed them among the goats.</p><p>They were first split off by Prussian naturalist Peter Simon Pallas in 1766, as a result of whom the name <i>Antilope</i> entered the scientific literature. In 1821, as part of a wider work on animal classification, English zoologist John Edward Gray divided the ruminating mammals into six families, naming five of them for the first time (having been beaten to naming the deer family by a single year). One of these was the "antelope family" which he distinguished from the cattle, sheep, and goats on the mistaken impression that their horns had a different internal structure.</p><p>Since then, Gray's "antelope family" has been demoted to subfamily rank, placed within the broader cattle family that includes all the true-horned ruminants. Furthermore, most of the species originally placed within it are now classified elsewhere... and this brings us to why antelopes don't exist.</p><p>The problem is that the animals we describe as "antelopes" aren't a single type of creature. They're actually multiple different types of animal defined as much by what they are not as by what they are. Effectively, the word "antelope" in English is commonly taken to refer to any member of the cattle family that isn't a cow, goat, or sheep of some kind. And that covers a fair bit of ground.</p><p>The modern rule on scientific naming is that all the members of a named group of animals must be more closely related to the other members of that group than they are to anything else. Or, to put it another way, that they must have evolved from a single ancestor that's unique to them. But the <a href="https://synapsida.blogspot.com/2016/08/bovines-largest-living-antelopes.html" target="_blank">spiral-horned antelopes</a> are more closely related to cattle than they are to, say, reedbuck, while oryxes are more closely related to goats than they are to impala. Come to that, the pronghorn "antelope" of North America isn't even a member of the cattle family at all - leading to arguments that it isn't "really" an antelope (which seem rather odd when you consider that, taxonomically speaking, neither is anything else).</p><p></p><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: right; margin-left: 1em; text-align: right;"><tbody><tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhla2_Q25qapAcbKv_bSDgZ3cYLJr8t1k38YKh1XIiT6v3ziObRS4RhyphenhyphentUWLIdWR9LBOMHBCg_XK2i22X6mxMfI2zYIxloMQW3alUAz2YY4swzf08zwv1A1VONsMV44WROON85V42mW1R2bHN1Frz2A40mxA_iGHwnMoXtZrTYCvwzx_YQQqTpgNWqMUDKF/s400/Bovidae-2.JPG" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="376" data-original-width="400" height="301" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhla2_Q25qapAcbKv_bSDgZ3cYLJr8t1k38YKh1XIiT6v3ziObRS4RhyphenhyphentUWLIdWR9LBOMHBCg_XK2i22X6mxMfI2zYIxloMQW3alUAz2YY4swzf08zwv1A1VONsMV44WROON85V42mW1R2bHN1Frz2A40mxA_iGHwnMoXtZrTYCvwzx_YQQqTpgNWqMUDKF/s320/Bovidae-2.JPG" width="320" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">A 2019 scheme for division of the cattle family<br />(Yes, this has changed since <a href="https://synapsida.blogspot.com/2016/01/bovids-and-bovines-what-makes-cow.html" target="_blank">the last time</a> I did one...)</td></tr></tbody></table>Ignoring the pronghorn for the sake of simplicity, anything we can say about antelopes in general is also going to be true of the entire cattle family. They are cloven-hoofed mostly herbivorous mammals with a four-chambered ruminating stomach. They have no incisors or canine teeth in the upper jaw, just a flat bony plate like a chopping board, and the lower canines are indistinguishable from incisors, being used only to clip plants, not to stab into fresh meat. The remaining teeth are separated from these by a wide gap, and are shaped so as to grind up tough vegetable matter. The males have permanent unbranched bony horns covered in a keratinous sheath, although these are usually either absent or at least much smaller in the females.<p></p><p>All of that is equally true of goats, sheep, and cows. But, once we concede that the term "antelope" actually covers multiple different kinds of animal, just how many kinds is that? There is inevitably a degree of subjectivity in this. Still ignoring the pronghorn, the cattle family tree is complex enough that our rule that every member of a group has to be more related to the rest of the group than to anything else means that there must be at least five such groups. In practice, modern scientists generally place non-pronghorn antelopes into more subfamilies than that - but exactly how many that should be is still <a href="https://doi.org/10.1016/j.bse.2012.12.005" target="_blank">controversial</a>.</p><p>Indeed, one scheme from 2021 has <a href="https://doi.org/10.1206/3970.1" target="_blank">only two</a> subfamilies, something achieved by not giving goats and sheep one of their own. More typically, there are about <a href="https://doi.org/10.1126/science.aav6202" target="_blank">ten</a> subfamilies within the cattle family, one of which is the caprines, which includes goats, sheep, and muskoxen, but not any antelopes. There is pretty much universal agreement that the bovines are another, including not just the cattle, bison, buffaloes, and yak, but also spiral-horned antelopes and a few others. I have described all of the <a href="https://synapsida.blogspot.com/search/label/caprines" target="_blank">caprine</a> and <a href="https://synapsida.blogspot.com/search/label/Bovines" target="_blank">bovine</a> species in detail previously on this blog, along with the <a href="https://synapsida.blogspot.com/2013/10/almost-caprine-chiru.html" target="_blank">chiru</a>, which still leaves us with <a href="https://doi.org/10.1644/1545-1542(2001)082%3C0374:ROFGNO%3E2.0.CO;2" target="_blank">seven kinds of antelope</a> left over.</p><p>One of these inevitably includes the animal that Pallas named <i>Antilope</i> all the way back in 1766 and that is the last remnant of Gray's "antelope family" of 1821. It's now a subfamily, the <b>Antilopinae</b>, and excludes the bovine antelopes, the chiru, and the other six groups - impalas, wildebeest, and so on. Despite this, it still has more species than any of the others.</p><p>These then, for lack of a better name, are the <b>antilopine antelopes</b>; the ones that are most closely related to the species that got the original scientific name. The antelopes as a whole may not exist, but these, which we could very loosely call "the typical antelopes" do. Even the two-subfamily scheme, which considers all the non-bovine bovids (including sheep and goats) to be "antilopine" recognises this group as a tribe - a named division within the larger subfamily.</p><p>There aren't many clear features that distinguish antilopine antelopes from other sorts, beyond the fact that genetic analysis shows that have a common ancestor that the others don't share. They tend to have a slim build and to live in arid or semiarid environments. They have large scent glands in front of their eyes, requiring visible pits in the skull to hold them, and they usually (but not always) have striped or otherwise patterned coats, helping to break up their outline and confuse predators when they run. The larger species have horizontal ridges running around their horns, although this is hardly unique. </p><p>They are found everywhere from South Africa to Tibet, which isn't exactly a small area. Over the course of this year, I will try and take a look at all of them. I will be starting next month, not with Pallas' <i>Antilope</i>, but with some species that are, perhaps, more familiar...</p><p><i>[Photo by <a href="https://commons.wikimedia.org/wiki/User:Nevit" target="_blank">Nevit Dilman</a>, from Wikimedia Commons. Cladogram adapted from <a href="https://doi.org/10.1126/science.aav6202" target="_blank">Chen et al. 2019</a>.]</i></p>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com5tag:blogger.com,1999:blog-4209921721314660731.post-54060691727062251602024-01-21T15:50:00.002+00:002024-01-21T17:11:18.702+00:00Rise of the One-Toed Horses<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjRd7sQ65DKtVVYmBXW2U9A3SAvvhRyjmhwIhiA5lxHCYCvbwAhSWHl2LEjZlS23QCWEe0pIBoNuBDoLfqnnwU4Phs12vPZQQnOiVXgEFTIukyszBagEMc414iTRgyZlW_f9X_NiYweGwedETvgbUalQVfT8oGGInrw8vI_VKTIuTSTwTYIgUncIfjtMth7/s400/Amerhippus_A6_digital.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="269" data-original-width="400" height="215" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjRd7sQ65DKtVVYmBXW2U9A3SAvvhRyjmhwIhiA5lxHCYCvbwAhSWHl2LEjZlS23QCWEe0pIBoNuBDoLfqnnwU4Phs12vPZQQnOiVXgEFTIukyszBagEMc414iTRgyZlW_f9X_NiYweGwedETvgbUalQVfT8oGGInrw8vI_VKTIuTSTwTYIgUncIfjtMth7/s320/Amerhippus_A6_digital.jpg" width="320" /></a></div>The horse family contains, depending on your definition, just seven or eight living species of wild animal. If you count them separately, you can add the two domesticated species to those (that is, the horse and the donkey) but that's it. Moreover, all of these species are so closely related to one another that they can interbreed, albeit usually to produce sterile offspring, and so are traditionally placed into a single genus: <i><b>Equus</b></i>.<p></p><p>The genus is noted for its members having just one toe on each foot. The story of how this happened, and the number of toes became reduced, is one of the most frequently repeated in mammalian evolution, although the detail may be more complex than is sometimes presented. The story of how the genus evolved since that point, however, is much less so.<span></span></p><a name='more'></a><p></p><p>There have been a great many <a href="https://doi.org/10.3390/biology11091258" target="_blank">fossil species</a> named within <i>Equus</i>, and it's unlikely that they're all genuinely distinct from one another. On top of that, we would also have to question just how close to modern horses a fossil has to be in order to place it within the same genus - we can hardly check to see if they crossbreed, after all. </p><p>Like all named ranks within biological classification, the concept of a genus is somewhat arbitrary. But given the fact that we use it as the first part of the scientific name and it's therefore rather important to our ability to communicate exactly what animal we're talking about, there have at least been attempts to come up with a definition of "genus".</p><p>One way of resolving the question is to simply admit that named ranks are fundamentally arbitrary, assume that the people who name living species at least know what they're doing, and say that we can place a fossil species <a href="https://doi.org/10.1093/sysbio/43.4.497" target="_blank">within a group</a> if it is descended from the last common ancestor of all living members of that group. This "crown group" definition is the narrowest possible one, although it still adds plenty of extinct species to <i>Equus.</i> Since the living genus includes at least three different kinds of animal - horses, asses, and zebras - so as long as you can say that your fossil is one of those three things, it must be part of the genus. (Of course, this definition doesn't work if the genus is entirely extinct, but that's a matter for another day).</p><p>Other definitions are broader, allowing us to acknowledge the similarity of some fossil species to living ones and avoid giving them all new names. One possibility is to say that a genus is a group of very closely related species that all share the same mode of life. In the case of <i>Equus</i>, that would be something like "adapted to living in open arid environments and eating low-quality roughage such as grass". Since the one-toed thing is (probably) an adaptation to <a href="https://doi.org/10.1007/BF01041590" target="_blank">running rapidly</a> across open plains that should also come close to our visual concept of what a horse should be. </p><p>In practice, some of the earliest known species of <i>Equus</i> probably don't fit that exact definition although they may fit with a <a href="https://doi.org/10.1023/B:IJOP.0000043354.36778.55" target="_blank">proposed guideline</a> of "you can call it a genus (or higher rank) if it's been around for at least five million years or so". Even then, it's difficult to know for certain, because to estimate when two different types of animal diverged we need genetic samples from both of them to see how much they have changed since their common ancestor lived, as well as fossil remains that we can use to calibrate how much time that amount of change is likely to have taken.</p><p>Using that technique, we can estimate that the common ancestor of zebras and asses probably diverged from the common ancestor of true horses around <a href="https://doi.org/10.1371%2Fjournal.pone.0055950" target="_blank">4 million years ago</a>, during the early Pliocene epoch. But with every other genus in the horse family thoroughly extinct, we can't do the same for <i>Equus</i> itself - there's nothing to compare it to. </p><p>Using the traditional naming scheme, however, the earliest known member of the horse genus is the Hagerman horse (<i>E. simplicidens</i>). This lived between about 5 and 3.5 million years ago in North America, with the original fossil being uncovered in Hagerman, Idaho in the 1890s. It physically resembled a modern zebra in size and shape, although obviously, we don't know anything about the colour. Some analyses have suggested that it may be the <a href="https://doi.org/10.1038/s41598-021-89440-9" target="_blank">common ancestor</a> of all living members of the horse family and literally the first member of the genus, but others imply that it's an early <a href="https://doi.org/10.3389/fevo.2019.00343" target="_blank">side branch</a>. In which case, under the stricter definitions of "genus", it has to be given a different name which, in this case, would be <i>Plesippus</i>.</p><p>In any event, it's clear that horses, as we know them today, first evolved in North America, and numerous other species are known from the continent over the last few million years. The last of them died out around 10,000 BC, presumably due to hunting by humans; it's unclear whether this was a now-vanished species or a <a href="https://doi.org/10.1007/s00239-008-9100-x" target="_blank">representative</a> of the modern horse. They even crossed into South America; the species <i><a href="https://doi.org/10.3389/fevo.2019.00235" target="_blank">E. neogeus</a></i> lived across much of the continent during the latter part of the Ice Ages, dying out <a href="https://doi.org/10.1016/j.palaeo.2015.02.026" target="_blank">around the same time</a> as its northern counterparts.</p><p>The reason that horses exist today at all is because, at some point, they left America by the northwesterly route and ended up in Eurasia, eventually spreading from there to Africa. This is conventionally thought to have happened in a single event 2.58 million years ago, which places it at exactly at the beginning of the Pleistocene epoch. So significant is this that it has a name: the <i>Equus</i> Datum. Essentially, the idea is that if you can find a fossil horse in a Eurasian rock deposit, that deposit must date to the Pleistocene or later. From an ecological point of view, the presence of horses can be said to <a href="https://doi.org/10.3389/fevo.2019.00278" target="_blank">define the line</a> between the Pliocene and the following epoch.</p><p>But how accurate really is that?</p><p>Certainly, there are fossil horses known from Eurasia that date right back to that time. That their first crossing can't have been any later than that isn't in dispute. Furthermore, they crossed the continent almost instantly from a geological perspective, since at least one of those very early fossil species, <i>E. major</i>, is known from as far west as <a href="https://doi.org/10.1016/j.quascirev.2023.108428" target="_blank">Italy</a>. Although it's worth mentioning that "almost instantly from a geological perspective" may still mean thousands of years...</p><p>Still, it wasn't necessarily a single event. For one thing, the ancestors of true horses had long since diverged from those of the other members of their genus by this point. So, as a bare minimum, two different species must have made the crossing and they didn't necessarily do so simultaneously. Indeed, we know of around <a href="https://doi.org/10.3389/fevo.2019.00429" target="_blank">five different species</a> that appeared in China almost immediately after the Datum, none of which are likely to be ancestors of the living sorts, so it's likely that several different kinds of horse took the opportunity to cross over to pastures new in the earliest part of the Pleistocene.</p><p>In between Europe and China, the first one-toed horse on the Indian subcontinent is <i>E. sivalensis</i>. This, too, goes back right to the Datum, and it survived until about 500,000 years ago, when it was replaced by <i>E. namadicus</i>, which in turn died out around 13,000 BC, just before the end of the Ice Ages. So similar are these two species that it has been <a href="https://doi.org/10.1016/j.quaint.2020.10.076" target="_blank">argued</a> that they are really the same animal, and even if they aren't, it's at least plausible that the one evolved directly into the other.</p><p>Judging from the remains we have, <i>E. sivalensis</i> was more closely related to asses and zebras than to true horses. Strictly speaking it was probably neither, although it was similar in size. The oldest fossil horses from Africa date to <a href="https://doi.org/10.1016/j.quascirev.2021.107116" target="_blank">2.44 million</a> years ago, 140,000 years after the <i>Equus</i> Datum in Eurasia. At least one of these, <i>E. tabeti</i>, appears to have been an early ass, and has been <a href="https://doi.org/10.1016/j.geobios.2019.12.001" target="_blank">suggested</a> as a direct ancestor of the modern domestic donkey. <i>E. koobiforensis</i>, which dates from 2.1 million years ago in Kenya may be the oldest known African zebra, although it's likely <a href="https://doi.org/10.1016/j.quascirev.2021.107155" target="_blank">closely related</a> to the slightly older <i>E. stenonis</i> from Greece.</p><p>It has been suspected for a while that <i>E. sivalensis</i> may actually predate the Pleistocene and a <a href="https://doi.org/10.1080/02724634.2023.2227236" target="_blank">recent study</a> confirms this, identifying a partial skull from just below the magnetic anomaly in the rock that, geologically speaking, defines the start of the epoch. So it looks as if the most significant event in the history of modern horses (other than their initial origin), the <i>Equus</i> Datum that distinguishes the start of the Pleistocene, does nothing of the sort. </p><p>Horses, it seems, snuck into Eurasia earlier than we'd thought.</p><p><i>[Picture by <a href="https://commons.wikimedia.org/wiki/User:Alex_Uchytel" target="_blank">Alex Uchytel</a>, from Wikimedia Commons.]</i></p>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com0tag:blogger.com,1999:blog-4209921721314660731.post-74848093961323480292024-01-14T14:15:00.000+00:002024-01-14T14:15:04.133+00:00Boys or Girls?<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjDdYuJI8ogEv71EQP2nz-vGOxpIdjV3kRqxQX2opqD0I80XciXBzGuvPeWTRtuhM_YozhloUKJOK7wdnnVu1hRGgpzVySTnZf5nlR_RYcAmRiJuXvb9TkW7eltwedqNutv3775sl1yhvhZtVl3FTfJ5KyKsalIxKZaI0G68wjSqxvxGBGQ2eBHnW-yxVxV/s400/Cervus_elaphus_Luc_Viatour_2.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="302" data-original-width="400" height="242" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjDdYuJI8ogEv71EQP2nz-vGOxpIdjV3kRqxQX2opqD0I80XciXBzGuvPeWTRtuhM_YozhloUKJOK7wdnnVu1hRGgpzVySTnZf5nlR_RYcAmRiJuXvb9TkW7eltwedqNutv3775sl1yhvhZtVl3FTfJ5KyKsalIxKZaI0G68wjSqxvxGBGQ2eBHnW-yxVxV/s320/Cervus_elaphus_Luc_Viatour_2.jpg" width="320" /></a></div>Generally speaking, a newborn mammal is equally likely to be male or female. The <b>sex ratio</b> in the resulting population may not always be a perfect 50/50 if one sex has a shorter life expectancy than the other, but it's still going to be pretty close. There is a sound reason for this, and it's called Fisher's Principle, after geneticist and mathematician Ronald Fisher, who promoted it in the 1930s (although he probably <a href="https://www.journals.uchicago.edu/doi/10.1086/286141" target="_blank">wasn't</a> the first to have thought of it).<p></p><p>The argument runs like this. Let's say that a particular species produces more females than males. Then males will have more mating opportunities than females, and will, on average, have more offspring. If a mutation then arises in a given individual that makes her more likely to give birth to sons, she will tend to have more grandchildren, many of whom will carry that mutation. Since they will also have an advantage, the mutation will spread through the population... until males are more common, at which point it's preferable to have more female offspring, and so on. <span></span></p><a name='more'></a><p></p><p>Thus, any bias in one direction should be swiftly cancelled out by a swing in the opposite one.</p><p>This is a general principle that should hold for any creature that reproduces in roughly the way that we do. In the case of mammals specifically, it's helped in large part by the way that sex is determined. Although there are a few odd exceptions, the general rule is that sex in mammals is determined by the sex chromosomes: males are XY and females are XX. Each ovum carries an X chromosome, and each sperm has either an X or a Y; these latter are produced by an <a href="https://en.wikipedia.org/wiki/Meiosis" target="_blank">even split</a> in the genetic material of the XY progenitor cells so that X-sperm and Y-sperm should be produced in exactly equal quantities, and be just as likely to fertilise any given egg. (And, yes, this is a specifically mammalian thing, reptiles, birds, and so on have different systems).</p><p>Except well, small problem here: it's not actually true. Well, not for every species, anyway: sometimes one sex really is more likely to be born than the other. It's not common and, at least in mammals, it's never a huge bias, but it <a href="https://doi.org/10.1111/j.1365-2656.2000.00454.x" target="_blank">does happen</a>. So... how and why?</p><p>To answer the second question first, Fisher's Principle relies on the assumption that it's equally easy to raise either sex to maturity. (In fairness to Fisher, he realised this, and made it explicit in his argument). If, say, females are more likely to die before breeding, you'll want to give birth to more of them so that it evens out when they reach adulthood. Or, since most male mammals leave home to find partners elsewhere, if resources are limited locally females, forced to stay where food is in short supply, will have a harder time of it than males, so it makes sense to <a href="https://doi.org/10.1016/S0022-5193(84)80066-1" target="_blank">produce more male offspring</a> so that they can go somewhere that's hopefully better. </p><p>For that matter, if it's just plain harder to raise offspring of one sex then, especially if you're not in peak condition (say, because you're <a href="https://doi.org/10.1016/j.theriogenology.2015.07.001" target="_blank">getting older</a>), you ought to produce more of the "easy" one - at least they'll survive. Then there's the "<a href="https://www.journals.uchicago.edu/doi/abs/10.1086/283709" target="_blank">sexy son</a>" hypothesis, which states that if a female's partner is particularly attractive, her sons are likely to be sexy too, so she should have more of them if she wants to maximise her number of grandchildren.</p><p>In reality, there are <a href="https://doi.org/10.1093/beheco/araa131" target="_blank">several reasons</a> why a sex bias could be advantageous, and they are not all mutually exclusive.</p><p>Well, all right... but how? The obvious assumption is that, since X and Y sperm should be produced in equal quantities, the mother is doing something during the very early stages of pregnancy that means one sex or the other is more likely to reach term. The only other choice she has would be to somehow determine which sperm were X or Y and ensure she is more likely to be fertilised by one than the other. Which may sound unlikely but, surprisingly, does appear to be <a href="https://doi.org/10.1093/beheco/araa131" target="_blank">possible</a> in at least some species.</p><p>Given that he's not the one with the womb, you'd think that the father gets less choice in the matter. But that's <a href="https://doi.org/10.1111/mam.12330" target="_blank">not necessarily true</a>, either.</p><p>There are, in fact, a number of ways that a male could potentially produce unequal amounts of X and Y sperm. There's no firm evidence that the initial creation of the two types can be biased, since, after all, you have to cut the initial XY set in half and messing that up would lead to other problems. But, after their formation, sperm cells have to go through several stages before they leave the male's body. If these can be affected, more sperm of one sex or the other might survive until required, as is seen, for example, in <a href="https://doi.org/10.1038/ncomms1700" target="_blank">pygmy hippos</a>.</p><p>There is some evidence that, if the male has fertility problems, those can affect his Y-sperm more often than those carrying the X chromosome, so if he does have children at all, they are more likely to be girls. This has been shown in both <a href="https://doi.org/10.1038%2Faja.2012.58" target="_blank">humans</a> and <a href="https://doi.org/10.1126/science.1133064" target="_blank">red deer</a>, but, since it's the result of something going wrong, it's not really a means of "controlling" things. (Plus, it's not entirely clear why this should be so).</p><p>It has been suggested that a male's frequency of mating may also have an effect on the sex ratio of his offspring. <a href="https://he02.tci-thaijo.org/index.php/sirirajmedj/article/view/55267" target="_blank">Abstinence</a> doesn't seem to make much difference, but the opposite might: one experiment on male rats showed that if they mated more often than they normally would, they eventually had <a href="https://doi.org/10.1016/0378-4320(88)90064-4" target="_blank">more daughters</a> than sons... although, again, we don't really know why.</p><p>In humans, there is some evidence to suggest that Y-sperm <a href="https://doi.org/10.1046/j.1439-0272.2001.00427.x" target="_blank">survive for longer</a> in the female reproductive tract than X-sperm. If that's true for other animals, a male could increase his chance of fathering sons by mating with his partner a few days before she ovulated... or she could adjust the odds by only letting him mate at the relevant time. Just after conception, higher levels of glucose in the reproductive tract of mice <a href="https://doi.org/10.1098/rspb.2007.1401" target="_blank">favour</a> the early survival of male embryos... something that the mother could theoretically control, but that the father could also influence by <a href="https://doi.org/10.1007/s00265-021-03032-1" target="_blank">producing</a> (or not) sugar-rich semen. Other components of the seminal fluid may also be relevant, since removal of the prostate in <a href="https://doi.org/10.1111/j.1365-2605.1986.tb00893.x" target="_blank">hamsters</a> makes them more likely to sire sons, so it's presumably doing something.</p><p>Much of this, however, while supported by observation, remains mysterious at a detailed level; it's more obvious <i>that</i> it's happening than <i>how</i> it's happening. A deeper understanding of the mechanisms involved could be advantageous, not just in agricultural animals - where one sex may be more useful to we humans than the other - but in conservation. </p><p>A <a href="https://doi.org/10.1093/jmammal/gyad067" target="_blank">recent study</a> on numbats at Perth Zoo showed that while the origin of the mother made no difference, males born in captivity tended to have more sons than those born in the wild and recently captured. That may be due to stress or being raised close to a higher number of other males than would be the case in nature, but understanding exactly why might help us devise better ways of preserving this particular endangered species.</p><p><i>[Photo by <a href="https://commons.wikimedia.org/wiki/User:Lviatour" target="_blank">Luc Viator</a>, from Wikimedia Commons.]</i></p>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com0tag:blogger.com,1999:blog-4209921721314660731.post-11449725282333588392024-01-07T16:04:00.003+00:002024-01-07T16:04:56.294+00:00The Rarity of Gophers<p><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody><tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhU2fUv469EHEhP6OCzwgjnvpOSdR75T-J49lVsuGC6tc5scEw_Haj24P_qfhZnM_WDjGyaN7ZwQuxLPZSN7yXry_EokTwEv40t9as1MAqSDh1wGD72EhCdN_eoqrhfIXtTOCnVOdnxzXVoXscwM-I0iLBr8bLkn3LDwAXyhg8TnXxxHsSpc1saL123Oc_-/s356/Wyoming_pocket_gopher.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="356" data-original-width="336" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhU2fUv469EHEhP6OCzwgjnvpOSdR75T-J49lVsuGC6tc5scEw_Haj24P_qfhZnM_WDjGyaN7ZwQuxLPZSN7yXry_EokTwEv40t9as1MAqSDh1wGD72EhCdN_eoqrhfIXtTOCnVOdnxzXVoXscwM-I0iLBr8bLkn3LDwAXyhg8TnXxxHsSpc1saL123Oc_-/s320/Wyoming_pocket_gopher.jpg" width="302" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;"><br /></td></tr></tbody></table>What exactly does it mean to say that a species is "rare"? The general idea, of course, is that it must have a lower total population than some species that is "common", and we can certainly argue over where to draw the line between the two. But, even then, rarity can manifest in different ways and that may have an effect on our perception of it.</p><p>Take the tiger for example. Today, this is undeniably a rare animal, and it's internationally listed as an endangered species. But go back two hundred years, and tigers were found across southern Asia from the easternmost parts of Turkey to the Russian Far East. They stretched from the deserts of Central Asia to the jungles of Java. But even then, if you'd gone to any of these places, the chances of actually meeting a tiger weren't all that high. Tigers are big predators, and they need a wide area to find enough food to eat. So they may have had a high total population (certainly compared with today) but they weren't exactly abundant in any given locality. Does that count as being "rare"?<span></span></p><a name='more'></a><p></p><p>In 1981, botanist Deborah Rabinowitz suggested a scheme that defined seven different types of rarity and which is still <a href="https://doi.org/10.1046/j.1365-2699.2000.00366.x" target="_blank">widely used today</a>. In fact, she placed species in eight categories, but one of these was "not rare"... and, in fact, turns out to have the smallest number of species in it, since there's only so much room in the world to put common species in. Among the other categories, we have species that, like the 19th-century tiger, are widespread and adaptable, but are never locally abundant. Then we have species that are only found in one, relatively small area (perhaps an isolated island) but are easy to find once you get there. Third are those species that are widespread but that have specific habitat requirements and so are found dotted about in particular locations across that area, densely clustering around some rare resource.</p><p>The remaining four categories cover the possible combinations of the first three: locally abundant but present in only specific parts of a small area, present in low numbers at multiple different locations, adaptable but living at low population levels in a small area, and living in small numbers at very specific parts of a location that isn't big to begin with.</p><p>This last category includes the species under the greatest potential threat and contains a surprisingly large number of species. For example, a 2011 study looking at prior research on 101 species of rare plants found that <a href="https://doi.org/10.1007/s10531-011-0007-2" target="_blank">30 of them</a> fell into this "rare in all three possible ways" category, making that by far the biggest category. These species are specialists, and there are so many of them because there's an advantage to outcompeting the generalists at one particular thing, and there are a great many possible things one could be good at. In the longer term, especially with issues such as rapid climate change, it's the more adaptable generalists that are likely to win out, but until then, finding a niche and sticking to it can have its benefits.</p><p>Or, at least that's the general assumption: that such species are rare because they are closely adapted to some resource that is itself rare. But there is another possibility for how this could happen. To see why, we can take a look at a couple of species of Spanish shrew. The greater white-toothed shrew (<i>Crocidura russula</i>) and Gueldenstädt's shrew (<i>C. gueldenstaedtii</i>) are both reasonably common and widespread species but a recent study found that, at least in one particular nature reserve in southern Spain, the latter is found only in <a href="https://doi.org/10.1093/jmammal/gyz203" target="_blank">tidal saltwater marshes</a>.</p><p>The initial thought might be that it really likes these sorts of marsh, but we know from its presence elsewhere that it's perfectly capable of living in other habitats (among other things, it's native to Austria, which is not known for its coastal wetlands). It turns out that, in all the other parts of the reserve, the greater white-toothed species outcompetes its smaller relative, dominating the environment. Gueldenstädt's species doesn't restrict itself to the marshes because it likes them but because it's the only local place that the greater species <i>doesn't</i> like - if anything, it's more generalist, willing to put up with substandard terrain if it at least doesn't have to share it.</p><p>Another potential example of this sort of effect concerns <b>gophers</b> in the western US, where some species are very widespread and others (unlike the shrews mentioned above) really are restricted to relatively small areas. Given that, on the face of it, the various kinds of gopher aren't that different from one another, why should that be?</p><p>The exact answer will probably depend on which particular species of gopher we are comparing, but a recently published study happened to look at the ones in Wyoming. There are three species of gopher in the state, one widespread and two that are more localised. The widespread species is the northern gopher (<i>Thomomys talpoides</i>) which is found from northern Arizona in the south to central Alberta in the north, and from inland California in the west to the Dakotas in the east. Clearly, this is not an animal with narrow habitat requirements.</p><p>Of the remaining two species, one lives predominantly in Idaho and only in a small part of western Wyoming adjoining that state. The other is known, appropriately enough, as the Wyoming gopher (<i>Thomomys clusius</i>) and, despite being very closely related to the more widespread species, lives only in a single patch of territory about 100 km (60 miles) across in the south of the state. That's small enough that it would normally qualify as a threatened species, and the only reason it doesn't is that its population seems to be stable, and there are no obvious threats to the environment in this <a href="https://www.google.co.uk/maps/@41.3481005,-107.7810194,69584m/data=!3m1!1e3?entry=ttu" target="_blank">largely uninhabited</a> area.</p><p>Even in this one place, northern gophers outnumber the Wyoming species about five to one, so we can't even say that the latter is locally abundant; it lives in a small area and has a (relatively) low population density even there. Significantly, within the area they are found only where one particular shrub, <a href="https://en.wikipedia.org/wiki/Atriplex_gardneri" target="_blank">Gardner's saltbush</a>, is also found, so the clue to the gopher's rarity is likely found in why that should be so important to them.</p><p>The first possibility that the researchers checked was whether it was all a coincidence; that Wyoming gophers happened to like the sort of soils that saltbush grows in, but didn't really care about the plants. At least from the perspective of soil chemistry that seems not to be the case; even where the soil is similar the gophers don't dig their burrows in the area if there aren't also saltbushes in it. So it really is the plants that they are looking for.</p><p>Being gophers, we'd reasonably assume that the reason they like the bushes is because they want to eat them, and, indeed, analysis of collected gopher droppings shows that this is what they do. The researchers followed this up by placing captive gophers in what they describe as a "cafeteria" where they were given the option of various different kinds of plants to eat to see which ones they preferred. Again, they weren't that fussed. The Wyoming gophers ate all the plants on the menu in about equal quantities and didn't seem to care whether saltbushes were included or not.</p><p>But, when they tried the same test with the northern gophers, they rarely touched the saltbushes on the menu at all, preferring spiny phlox, an American wildflower, and eating the other options in about the same quantities as the Wyoming species did. Since saltbushes get their name from the high salt content of their leaves, one imagines that the northern gophers just didn't like the taste - they're not fans of well-seasoned salads.</p><p>Just as with the Spanish shrews, the widespread northern gophers are much larger than the Wyoming species, and can presumably outcompete them whenever the two live directly side by side. Whether they eat up all the food first, physically make life difficult for their smaller relatives, or are doing something else, they always come out on top. Unless the main vegetation is icky, unpleasant, saltbushes, which the northern gophers avoid, but the Wyoming gophers don't care about. They're not specifically looking for the plants and would happily eat something else if they could, but it's their best chance for a quiet meal. While the bushes are found in other parts of North America, they can't get there because the northern gophers stop them from travelling through intervening terrain where the plants are scarce.</p><p>They don't especially like saltbushes, but they're good enough, and nobody else wants them...</p><p><i>[Photo by the <a href="https://www.fws.gov/" target="_blank">US Fish and Wildlife Service</a>, in the public domain.]</i></p>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com0tag:blogger.com,1999:blog-4209921721314660731.post-52227814810523503492023-12-17T18:04:00.002+00:002024-01-27T11:39:49.593+00:00Prehistoric Mammal Discoveries 2023<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody><tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgMbwfpGNVW_CmJ6Z3ojk-IU3b7exFSPu0TDLbJZgxNwtztFYZor4Dn0lxSmbHVDPf39hHyQF29r16zGbinO2p0vWAZ9s0NScaETEkDoA-pM6VXm-k2mRTG_GfvFjuQGng6ROMTAXtzZPuB-8RjfkL8K5j-WQzmMfEWgDa9LQtAVrnBk2ecNRDKItJbmrUH/s400/42003_2023_5135_Fig1_HTML.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="248" data-original-width="400" height="198" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgMbwfpGNVW_CmJ6Z3ojk-IU3b7exFSPu0TDLbJZgxNwtztFYZor4Dn0lxSmbHVDPf39hHyQF29r16zGbinO2p0vWAZ9s0NScaETEkDoA-pM6VXm-k2mRTG_GfvFjuQGng6ROMTAXtzZPuB-8RjfkL8K5j-WQzmMfEWgDa9LQtAVrnBk2ecNRDKItJbmrUH/s320/42003_2023_5135_Fig1_HTML.jpg" width="320" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;"><i>Potamotherium</i></td></tr></tbody></table>It's the last post of the year for 2023, and that means it's time once again to take a brief look at discoveries from the last year in the world of fossil mammals that didn't make it into this blog. Because, while dinosaurs are undoubtedly popular, the study of prehistoric mammals is also a major field, aided by that, being (mostly) relatively recent they tend to be more numerous and better preserved. Of course, everyone's heard of woolly mammoths and sabretooth cats but there's plenty more out there and, if I'm going to zip through them at speed today, I'm also going to try and cover as wide a range as possible. So, let's get going...<span><a name='more'></a></span><h3 style="text-align: left;"><br /></h3><h3 style="text-align: left;">Large Herbivores</h3><div>While there have been several new species of fossil mammal identified this year, sometimes we can learn new information by re-studying old fossils with new methods. One of the most frequent questions from lay people about any new fossil animal is "how big was it?" and this isn't always easy to determine when all you have is an incomplete skeleton. A study published this year developed <a href="https://doi.org/10.1002/jmor.21636" target="_blank">a new method</a> for estimating the weight of fossil ruminants from the shape and size of the leg bones that had to support them. Using over 100 living species to calibrate their results, they estimated that the late Ice Age <b>bison</b> <i>Bison antiquus</i> weighed 800-880 kg (just under a ton), not so different from the modern species.</div><div><br /></div><div>Pollen analysis from the teeth of an Irish <b>deer</b> (<i>Megalaceros giganteus</i>) that lived in the Netherlands during a gap between the last two Ice Ages indicated that it had been <a href="https://doi.org/10.1016/j.revpalbo.2023.105021" target="_blank">eating a diet</a> of hogweed, chervil, chamomile, groundsel, and comfrey along with grasses, suggesting cool open woodlands rich in herbs. Elsewhere, another Irish deer was <a href="https://doi.org/10.3390/d15020299" target="_blank">discovered</a> in 35,000-year-old deposits in Catalonia, Spain, much later than they had been thought to survive in the area - its recent ancestors had possibly taken a trip around one end of the Pyrenees when southern France became too cold to inhabit.</div><div><br /></div><div>A newly discovered <a href="https://doi.org/10.1080/02724634.2022.2163176" target="_blank">assemblage</a> of fossils of <i>Neotragoceros</i>, the earliest known member of the <b>cattle</b> family in North America, showed that their closest living relatives were the nilgai "blue bulls" of India, living in Oregon 6 million years ago. Meanwhile, <i>Procobus</i>, a Late Miocene animal from northern Greece, was shown not be a relative of reedbuck antelopes, as previously thought, but <a href="https://doi.org/10.1016/j.palwor.2023.06.008" target="_blank">more likely</a> related to the common ancestor of sheep and goats.</div><div><br /></div><div>A fossil <b>horse</b> (<i>Equus sivalensis</i>) discovered in northern India was <a href="https://doi.org/10.1080/02724634.2023.2227236" target="_blank">dated</a> to over 2.6 million years ago, during the Late Pliocene; if true, this suggests that modern-type horses entered Eurasia earlier than thought, prior to the Ice Ages. Emigrating in the opposite direction, and perhaps not much earlier, a newly discovered fossil <b>tapir</b> (<i>Tapirus arvenensis</i>) from northern Spain seems to be surprisingly <a href="https://doi.org/10.1080/14772019.2023.2250117" target="_blank">closely related</a> to the modern tapirs of Indonesia and Southeast Asia.</div><div><br /></div><div>Among the really large herbivores, <b>mammoths</b> have the advantage of having died out recently enough that we can do research on their remains that wouldn't be possible on fossils that had entirely turned to rock. Analysis of the strontium isotopes in the teeth of a woolly mammoth (<i>Mammuthus primigenius</i>) showed that it had <a href="https://doi.org/10.1016/j.quascirev.2023.108036" target="_blank">migrated</a> from winter grazing grounds in southern Poland to cooler climes 250-400km (155-250 miles) further north each summer for at least 12 years. Genomic analysis of other individuals was able to <a href="https://doi.org/10.1016/j.cub.2023.03.084" target="_blank">identify genes</a> responsible for hair growth, fat deposition, and immune function that distinguished them from modern, tropical, elephants. Furthermore, analysis of the tusks of a male woolly mammoth was able to identify the presence of <a href="https://doi.org/10.1038/s41586-023-06020-9" target="_blank">testosterone</a>, deposited in such a way as to suggest it experienced the same periodic bouts of sexually-charged "musth" as living elephants do.</div><div><br /></div><div>It isn't just woolly mammoths, either. Genetic studies on woolly <b>rhinos</b> (<i>Coelodonta antiquitatis</i>) showed that the Siberian populations <a href="https://doi.org/10.1098/rsbl.2023.0343" target="_blank">diverged</a> shortly after the first emergence of the species in Europe, and that, in times when northern Asia was covered in vegetation-free ice sheets, they sought refuge and diversified in <a href="https://doi.org/10.1186/s12862-023-02168-0" target="_blank">northern China</a> before later returning. Among non-mammoth <b>elephants</b>, studies on American mastodons (<i>Mammut</i> spp.) added <a href="https://journals.oregondigital.org/nat_history/article/view/6004" target="_blank">further weight</a> to the theory that they evolved on the continent, rather than being the product of an emigration of apparently similar animals known to have lived in Asia. A study on the skulls of the Miocene shovel-tusker <i>Platybeladon</i> indicated that it may have been the first "elephant" to develop a prehensile <a href="http://10.7554/eLife.90908.1" target="_blank">trunk</a>, five million years before the modern elephant family.</div><div><br /></div><h3 style="text-align: left;">Carnivores</h3><div>This year saw a new description of a fossil jawbone previously found in Alberta, Canada, confirming that it probably belonged to a <a href="https://doi.org/10.1002/jqs.3516" target="_blank">dire wolf</a> (<i>Aenocyon dirus</i>), not a modern grey wolf as had been suggested; this would make it the most northerly known example of the species, and the only one from Canada. Elsewhere, an analysis of the skull of the early <b>dog</b> <i>Eucyon</i> from Pliocene France indicated a <a href="https://doi.org/10.3389/fevo.2023.1173341" target="_blank">jaw strength</a> suited to biting smallish prey that fights back, implying a diet similar to some of the larger modern jackals, and perhaps related to the rapid evolution of rabbits and hares at the time. Focussing on an entirely different part of the skeletal anatomy, a study of the <a href="https://doi.org/10.1371/journal.pone.0280327" target="_blank">penis-bones</a> of three species of borophagine including the giant bone-crushing dog <i>Aelurodon</i>, showed that they mated in the same way that modern dogs do but were, for entirely mysterious reasons, distinctly curved.</div><div><br /></div><div>An analysis of three species of carnivorous panda placed in a new genus, <i>Huracan</i>, with fossils found in Spain, China, and North America showed that they were suited to open habitats, being able to <a href="https://doi.org/10.1206/3996.1" target="_blank">chase down</a> their prey. While there is no doubt that pandas are a kind of <b>bear</b>, this is less clear for some other fossils first described this year. <i>Lonchocyon</i>, dating back to the late Eocene over 33 million years ago, was about the size of a large dog and likely killed its prey with a powerful bite... but it has features shared <a href="https://doi.org/10.3389/feart.2023.1137891" target="_blank">with both</a> early bears and the related, but extinct bear-dogs, so it's unclear which, if either, it was more closely related to. <i>Eoarctos</i> is almost as old and, if not quite a bear, may be closer to them than to anything else alive today. A <a href="https://doi.org/10.1080/02724634.2022.2145900" target="_blank">description</a> of a newly discovered skeleton, shows that it had the unusual combination of limbs suited for climbing trees and teeth suited to eating shellfish; perhaps it just used the trees to hide from larger predators.</div><div><br /></div><div>Among the <b>cats</b>, a new analysis of the <a href="https://doi.org/10.1098/rsbl.2022.0483" target="_blank">elbows</a> of the "American cheetah" (<i>Miracinonyx trumani</i>) reveals it to be as much like that of its actual relative, the puma/cougar/mountain lion as it is like its Old World namesake suggesting that, while it was undeniably fast-running, it may have been less like a true cheetah in its lifestyle than previously thought. On the other hand, a study on the jaws of cave lions (<i>Panthera spelaea</i>) confirmed that the males were, indeed, <a href="https://doi.org/10.1080/08912963.2023.2214578" target="_blank">larger</a> than the lionesses, much like their modern relative. </div><div><br /></div><div>A four-million-year-old fossil cat from the Tibetan Plateau has been <a href="https://doi.org/10.1007/s12549-023-00571-5" target="_blank">proposed</a> as an early relative of the modern clouded leopard and given a new genus, <i>Palaeopanthera</i>; it had previously been identified as a snow leopard. Further south, in Thailand, the newly described big cat <i>Pachypanthera</i> is not thought to be closely related to any living species, being older than any of the known "roaring cats" at up to 9 million years old, and having <a href="https://doi.org/10.1007/s00114-023-01867-4" target="_blank">exceptionally powerful</a> jaws and teeth. It was about the size of a modern lioness and the jaws are so strong compared with living species that it may have had some ability to crack bone like a hyena.</div><div><br /></div><div>As for sabretooths, a new analysis of the hyoid bones of <i>Smilodon</i> suggests that, contrary to many depictions in fiction, it probably <a href="https://doi.org/10.1002/jmor.21627" target="_blank">couldn't roar</a>, instead making sounds similar to those of a cougar, but deeper in tone. On the other hand, the fossil paw of another sabretooth, <i>Amphimachairodus,</i> showed that it had been so badly injured as to be useless. This ought to have resulted in the animal starving to death shortly afterwards... yet the paw had partially healed. This implies that it must have <a href="https://doi.org/10.1098%2Frspb.2023.0019" target="_blank">hunted alongside</a> others of its kind, which helped to feed it, and supports other lines of evidence that this sabretooth cat at least, was a pack hunter, not solitary as most big cats (other than lions) are today.</div><div><br /></div><h3 style="text-align: left;">Other Land-dwelling Placentals</h3><div>In recent years, a number of fossil species belonging to the subfamily of "African <b>apes</b>" (as opposed to orangutans and gibbons) have been discovered outside that continent, from the eastern Mediterranean. This has cast doubt on the long-held assumption that African apes originated in... well, Africa. A <a href="https://doi.org/10.1038/s42003-023-05210-5" target="_blank">newly described</a> fossil species, <i>Anadoluvius</i>, from Turkey, adds to the debate by being one of the oldest known members of the subfamily at 8.7 million years old, suggesting that, while humans clearly originated in Africa, their own ancestors may well have come from further north. </div><div><br /></div><div><i>Sahelanthropus</i> is a known species of ape living somewhat later, around 7 million years ago. A new analysis of its arm bones suggests that it <a href="https://doi.org/10.1016/j.jhevol.2023.103355" target="_blank">knuckle-walked</a> like a chimp or gorilla, adding to earlier evidence that it was not bipedal, as had once been thought. It remains unclear whether it was related to the common ancestor of chimps or humans, or was actually an early gorilla. <i>Gigantopithecus</i>, an ape which lived in China during the Ice Ages, had amongst the <a href="https://doi.org/10.1016/j.jhevol.2022.103313" target="_blank">strongest bites</a>, and the thickest teeth, of any known ape species (exceeded only by "nutcracker man" <i>Paranthropus</i>) suggesting that whatever sort of vegetation it ate was particularly difficult to chew, possibly including tough roots that would inevitably have been mixed in with grit.</div><div><br /></div><div>This year also saw the description of two new fossil <b>squirrels</b> (<i>Junggarisciurus</i> and <i>Eopetes</i>) from Xinjiang in China. They are the <a href="https://doi.org/10.3389/feart.2022.1004509" target="_blank">oldest known squirrels</a> from Asia, dating back around 35 million years, and thus equal in age to the previous oldest squirrel fossils, which were found in North America. Those were ground squirrels, but these, although large at up to 2.7 kg (9 lbs), more closely resemble tree-living species, implying that, since their North American counterparts were not, the split between tree and ground squirrels could date back almost to the origins of the family. Elsewhere, studies of skeletons of the giant Menorcan rabbit <i>Nuralagus rex</i> - it weighed at least 8 kg (18 lbs) - showed that, as expected, it <a href="https://doi.org/10.1016/j.isci.2023.107654" target="_blank">grew very slowly</a> throughout its life, probably being able to afford to do so since it lived on only on an isolated island devoid of predators.</div><div><br /></div><div>Two analyses, one on the <a href="https://doi.org/10.1002/jqs.3534" target="_blank">limb bones</a> and one on the <a href="https://doi.org/10.1007/s10914-023-09681-5" target="_blank">teeth and jaws</a> of various different kinds of <b>ground sloth</b>, came to similar conclusions. The researchers (and it's mostly the same ones) interpreted their results to mean that the nothrothere and megalonychid ground sloths, which are related to the modern three-toes species, would have been skilled at climbing, while the mylodontid sloths, related to the modern two-toed species, were specialised for digging and had an unusually broad diet. The giant megatheres, which are also related to the three-toed sloths were, perhaps unsurprisingly, purely ground dwellers. The discovery of the fossil of a <i>Nothrotherium</i> ground sloth that had died whilst in a late stage of <a href="https://doi.org/10.1007/s10914-023-09665-5" target="_blank">pregnancy</a> showed features on the foetus that imply adaptations to relatively rapid weaning and limbs that could easily have gripped onto its mother's fur to be carried about, as well as demonstrating that, like modern sloths, these particular ground sloths gave birth to a single young at a time.</div><div><br /></div><div>This year also saw the description of the <a href="https://doi.org/10.1371/journal.pone.0283505" target="_blank">oldest known</a> fossil <b>bats</b> so far, assigned to the genus <i>Icaronycteris</i>. 52 million years old, these were found in Wyoming, and do not belong to any of the modern families, nor do they seem particularly closely related to any of them. Taken together with the fact that the next oldest bats are from France, and not that much younger, this indicates that even at this early date, bats were already diverse and widespread, probably having gone a rapid burst of evolution not long after the extinction of the non-avian dinosaurs.</div><div><br /></div><h3 style="text-align: left;">Aquatic Mammals</h3><div>An analysis of the inside of the skull of <i>Potamotherium</i>, thought to be a semi-aquatic ancestor of <b>seals</b>, was able to get a good idea of the shape of its brain. This showed that the parts of the brain used in modern seals to interpret sensations from their <a href="https://doi.org/10.1038/s42003-023-05135-z" target="_blank">whiskers</a> when searching for food underwater were already well-developed in an animal that presumably lived more like an otter. A similar analysis of the <a href="https://doi.org/10.1093/zoolinnean/zlac112" target="_blank">inner ears</a> of anthracotheres, semi-aquatic animals related to both <b>hippos</b> and the ancestors of whales, showed that their sense of hearing became increasingly adapted to underwater life as they evolved, implying that their last common ancestor with hippos still lived on dry land, and their aquatic habits evolved independently.</div><div><br /></div><div>Among <b>cetaceans</b>, a few species with unusual feeding habits were reported this year. A newly described species of the early sperm whale <i>Diaphorocetus</i> had small teeth like modern species, but had a different shape to the head suitable for rapidly sweeping from <a href="https://doi.org/10.5252/geodiversitas2023v45a22" target="_blank">side to side</a> to snap at prey - quite unlike either modern sperm whales or the large-toothed "macroraptor" sperm whales of the past such as <i>Livyatan</i>. The teeth of a newly described dolphin-sized animal from New Zealand, <i>Nihohae</i>, had <a href="https://doi.org/10.1098/rspb.2023.0873" target="_blank">multiple tusks</a> projecting out horizontally from the tips of a long and narrow snout, quite unlike any modern cetacean. Since the teeth were unworn, they can't have been used to poke about for prey in the mud and they would not have been much use for biting; the discoverers' best guess is that it whacked at fish with a sideways swipe, rather like a sawfish.</div><div><br /></div><div>On the other hand, the skull of the oldest known member of the modern toothed whale group, <i>Simocetus</i>, which lived 32 million years ago in the North Pacific suggests that it had already adopted a modern style of suction-feeding even though it <a href="https://doi.org/10.7717%2Fpeerj.15576" target="_blank">had yet to fully develop</a> ultrasonic hearing. Finally, no discussion of prehistoric whale discoveries this year can fail to mention an analysis of the skeleton of <i>Perucetus collosus</i>. Gaining weight to serve as ballast when diving to shallow depths, the skeleton was so massive that the report suggests that this may have been the <a href="https://doi.org/10.1038/s41586-023-06381-1" target="_blank">heaviest animal</a> ever to have lived, at up to 340 tons... and, yes, that would be heavier than a blue whale, even if the bodily dimensions were not quite so vast.</div><div><br /></div><h3 style="text-align: left;">Marsupials and More</h3><div>Analysis of the small Ice Age marsupial <i>Bohra</i> this year elaborated on its <a href="https://doi.org/10.11646/zootaxa.5299.1.1" target="_blank">adaptations</a> as a probable ancestor of modern tree-kangaroos. While the hind feet initially had a similar skeletal structure to those of the sort of kangaroos we normally think of, later species within the genus developed more flexible ankles suitable for climbing as forests became more extensive in Australia in the early Pliocene, 5 million years ago. The researchers argue that <i>Bohra</i> probably had a lifestyle similar to some prehistoric lemurs. </div><div><br /></div><div>While we're up in the trees, another new fossil, <i>Lumakoala</i>, was identified as belonging to what's probably an <a href="https://doi.org/10.1038%2Fs41598-023-41471-0" target="_blank">early koala</a>. At no more than 2.5 kg (5½ lbs), if it's what it appears to be, it must have been one of the smallest <b>koalas</b> ever, and its molar teeth were still primitive, not yet highly adapted to munching on tough leaves. Meanwhile, a new analysis of <i>Nimbadon</i>, a Miocene tree-climbing marsupial that looked like a koala, but instead belonged to a now-extinct group, suggests that it ate a large amount of <a href="https://doi.org/10.1038%2Fs42003-023-04624-5" target="_blank">fruit</a> instead of leaves, thus behaving more like a typical primate and likely having no direct competitors at the time. Which probably explains what it was doing up a tree when it weighed about 70 kg (150 lbs).</div><div><br /></div><div>The <b>marsupial sabretooth</b> <i>Thylacosmilus</i> is notable for the bony flanges on its jaws that protect the exceptionally large sabres. But this isn't the only thing odd about it; its eyes were on the sides of its head, the sort of thing that's entirely reasonable on a horse that wants to keep a wide-angle view of its surroundings but that seems rather odd on a predator that wants to pounce on prey. A new analysis, however, shows that the exact shape of the eye sockets means that the animal would have had better <a href="https://doi.org/10.1038%2Fs42003-023-04624-5" target="_blank">binocular vision</a> than might be expected and that the eyes had to be pushed to the side to make space for the bases of its enormous teeth. </div><div><br /></div><div>This year also saw the description of the tooth of a <b>monotreme</b>, distantly related to modern platypuses, from southern Argentina. This is significant, because, at around 70 million years old, it's <a href="https://doi.org/10.1038%2Fs42003-023-04498-7" target="_blank">well before</a> the only previously known monotreme fossil from outside of Australasia - the mere existence of which had been a bit of shock when it was described in 1992.</div><div><br /></div><div>Last of all, I have to mention an extraordinary fossil of <i>Repenomamus</i>, a badger-sized carnivorous mammal not closely related to anything alive today. The fossil shows it locked in deadly <a href="https://doi.org/10.1038%2Fs41598-023-37545-8" target="_blank">mortal combat</a> with <i>Psittacosaurus</i>, a small bipedal early relative of the more famous <i>Triceratops</i>. Its teeth are firmly clamped onto the dinosaur's front leg and its forepaw is holding down its opponent's jaw. Had the pair not been suddenly buried in hot ash from an erupting volcano it's very likely that this particular dinosaur would have lost the fight.</div><div><br /></div><div>Score one for mammals.</div><div><hr /><p class="MsoNormal" style="line-height: normal; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><span style="font-family: "Times New Roman",serif; font-size: 12pt; mso-fareast-font-family: "Times New Roman"; mso-fareast-language: EN-GB;"></span></p><div style="text-align: center;"><b>Synapsida is taking a break for the holiday period and will return on the 7th January</b></div></div><div><br /></div><div><i>[Picture by <a href="https://www.nature.com/articles/s42003-023-05135-z/figures/1" target="_blank">Gabriel Ugueto</a>, available under the <a href="https://creativecommons.org/licenses/by/4.0/" target="_blank">CC BY 4.0</a> license.]</i></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com1tag:blogger.com,1999:blog-4209921721314660731.post-41585517563730422982023-12-10T16:43:00.002+00:002024-02-18T09:14:58.890+00:00Oligocene (Pt 6): Devil's Corkscrews and the Grasseater That Wasn't<p></p><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody><tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEguK8ieCxdbLOJmoUKDj5hBYydOlLQ8n1QShoMawHbYH-fLHCt3pfKAJbtG6sct-gfPpLcnatPY2yaP_WHN9jgZo6yZ2N4h-utaK5JLN-yaaXdyk4oKa6AMZEMEtHO26CwyC9L0F03aQ_R5T4r3-em2Z5E22sOEYoShSp3W7BhbeP4icQKkSGc7Jved0F2B/s400/Leptomeryx_1.JPG" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="297" data-original-width="400" height="238" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEguK8ieCxdbLOJmoUKDj5hBYydOlLQ8n1QShoMawHbYH-fLHCt3pfKAJbtG6sct-gfPpLcnatPY2yaP_WHN9jgZo6yZ2N4h-utaK5JLN-yaaXdyk4oKa6AMZEMEtHO26CwyC9L0F03aQ_R5T4r3-em2Z5E22sOEYoShSp3W7BhbeP4icQKkSGc7Jved0F2B/s320/Leptomeryx_1.JPG" width="320" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;"><i>Leptomeryx</i></td></tr></tbody></table>The Grande Coupure was, strictly defined, an event unique to Europe, caused by the drying up of the water channels separating it from Asia. However, it was compounded by a dramatic worldwide cooling event, and, if the Coupure itself didn't affect more distant lands, the climate changes certainly did. Due to some particularly well-preserved geological deposits of the right age, as well as the obvious convenience for Western researchers, this is particularly well-studied in North America.<p></p><p>Deposits across the continent show a <a href="https://doi.org/10.1016/S0031-0182(00)00248-0" target="_blank">sudden change</a> in the climate at around the dawn of the Oligocene. By 'sudden' in this context, we mean over the course of hundreds of thousands of years, so it's hardly something you would have noticed had you been there at the time, but it's still rapid as such things go. The exact nature of the changes, and the speed at which they appear to have happened, depend on which part of the continent we're talking about, but nowhere was unaffected.<span></span></p><a name='more'></a><p></p><p>Take <a href="https://doi.org/10.1016/0031-0182(94)90233-X" target="_blank">Oregon</a>, for example. At the end of the previous epoch, this was covered in damp, subtropical woodlands, with annual temperatures around 21°C (70°F) and rainfall around 180 cm (70 inches). So, basically, Seattle would have had a climate like the one Tallahassee does today. A million years later, annual mean temperatures had dropped to 12°C (54°F) and the rainfall had halved, both of which are in the ballpark of what we'd expect in the state today. Notably, however, this temperature drop wasn't even, with winters cooling by far more than summer did, so that plants, and the animals that fed on them, not only had to cope with cooler temperatures overall, but a much bigger variation over the course of the year.</p><p>Similar patterns are seen <a href="https://doi.org/10.1016/S0031-0182(00)00248-0" target="_blank">elsewhere</a>, with the continent becoming drier as well as colder (compared to the sweltering conditions it had been in before, at any rate). Some of the evidence for this comes from fossil leaf impressions, showing how denser, moist, forests gave way to drier open woodland across much of the continent, with a shift in the species of tree found within them. A decline in the number of fossil freshwater turtles, crocodiles, and salamanders also reflects the drier conditions... but, surprisingly, the changes among mammal species seem to have been <a href="https://doi.org/10.1016/S0031-0182(96)00099-5" target="_blank">comparatively mild</a>.</p><p>There was, for example, less change among rodents than we might expect, and certainly less change than occurred in Europe. <i>Agnotocastor</i>, for example, an early <b>beaver</b>, seems to have made it through the transition just fine. It's both the oldest and most primitive beaver known and may represent the <a href="https://doi.org/10.1023/A:1014468732231" target="_blank">ancestral stock</a> from which all later beavers evolved - although it's sufficiently <a href="https://doi.org/10.7717/peerj.3311" target="_blank">similar</a> to the Oligocene Eurasian <i>Propaleocastor</i> that it's not immediately clear on which of the two continents beavers first appeared. </p><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: right; margin-left: 1em; text-align: right;"><tbody><tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhGmNBngBuS0T25gSYIyz0u-rBXI7Jh5Y8G2QhlGnc4H0-8EOy9o8xVzVsqu-7pZM7aUHmMLpvpjjIDeEHQivVfe2_20yR6iA4abWwaMjc7gBpT0Xk5h4e2zoYIqivhNbx5qHAlZgFgoqJXdgmlqQTBhk59A_vdSsRDfiuXE7BHBp-2bjaZlDIrLtkwYrhE/s400/Palaeocastor.jpg" style="margin-left: auto; margin-right: auto; text-align: center;"><img border="0" data-original-height="400" data-original-width="300" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhGmNBngBuS0T25gSYIyz0u-rBXI7Jh5Y8G2QhlGnc4H0-8EOy9o8xVzVsqu-7pZM7aUHmMLpvpjjIDeEHQivVfe2_20yR6iA4abWwaMjc7gBpT0Xk5h4e2zoYIqivhNbx5qHAlZgFgoqJXdgmlqQTBhk59A_vdSsRDfiuXE7BHBp-2bjaZlDIrLtkwYrhE/s320/Palaeocastor.jpg" width="240" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">Devil's corkscrew<br />- note the fossil of its excavator</td></tr></tbody></table><p>By the late Oligocene, <i>Agnotocastor</i> had been replaced by <i>Palaeocastor</i> and related "burrowing beavers". Smaller than modern beavers, these likely spent little, if any, time in rivers, instead being adapted for digging deep burrows in which to shelter, and may have physically resembled a prairie dog. Initially <a href="https://doi.org/10.1007/s10914-013-9231-8" target="_blank">scratch-diggers</a>, they later evolved towards a more efficient use of chisel-like teeth to excavate soil and left no modern descendants, dying out in the early Miocene. They are best known for the <a href="https://doi.org/10.1016/0031-0182(77)90027-X" target="_blank">fossil remains</a> of the burrows, tight helical tunnels descending into the earth for up to 3 metres (10 feet) and now formed into bizarre rocky shapes known as "devil's corkscrews". Since the remains of potential predators have occasionally been found inside the burrows, they can't have been very effective as a means of defence and were more likely a protection against <a href="https://doi.org/10.1016/S0031-0182(98)00157-6" target="_blank">cold weather</a>.</p><p><i>Palaeolagus</i> was another small mammal that made it through the transition, and one that lasted until at least the end of the Oligocene. Originally thought to be an early <b>rabbit</b>, judging from the number of fossils found this must have been a common and widespread animal. More recent analysis has shown that, while it is a lagomorph, its skeleton has a <a href="https://doi.org/10.3389/fevo.2021.634757" target="_blank">mix of features</a> of the two living lagomorph families, placing it as neither a rabbit nor a pika, but a member of a now-extinct family that had, perhaps, changed little from their last common ancestor. The internal shape of the skull reveals that the parts of the brain related to the sense of smell were proportionately <a href="http://doi.org/10.58809/YWVG7861" target="_blank">larger</a> than in modern lagomorphs, while those of its close relative <i>Megalagus</i> suggest that, while we'll likely never know whether it had rabbit-like ears, it had already evolved <a href="https://doi.org/10.1002/ece3.9890" target="_blank">keen hearing</a>. At least some of its other close relatives were adapted for <a href="https://doi.org/10.1206/3773.2" target="_blank">running</a> across open ground, rather than hopping.</p><p><b>Camels</b> likely began to diversify towards the end of the previous epoch, but they seem to have become a more significant part of North American wildlife during the Oligocene. The best-known Oligocene camel is <i>Poebrotherium</i>, although usually considered distinct from both true camels and the llamas and their relatives. Indeed, those two groups did not appear until much later, perhaps not long before one left their original home continent for Asia, and the other for South America. </p><p>Although <i>Poebrotherium</i> was not an especially close relative of the modern species, it had taken a significant step in their direction by developing the two-toed cloven foot, as well as becoming much larger than its ancestors, reaching about the size of a sheep or a gazelle. While it probably looked quite llama-like in other respects, a gazelle is a good analogy, since <i>Poebrotherium</i>'s long legs would have made it a fast runner - possibly the fastest animal on the continent at the time. Although the scientific name literally translates as "grass-eating beast", studies of the <a href="http://npshistory.com/series/symposia/fossil-resources/6/proceedings.pdf" target="_blank">shape of the teeth</a> suggest that grass was a relatively minor component of its diet, although whether it was a dedicated browser on leafy shrubs or more of a mixed feeder is uncertain.</p><p>While <i>Poebrotherium</i> survived throughout the whole of the Oligocene, it was joined by other species of 'camel' later on. <i>Paratylopus</i> is perhaps the most significant example, notable for being the first to have the long neck seen in modern species. Others include <i>Miotylopus</i>, another gazelle-sized animal, but one that probably did feed on grass. None of these, at this point, inhabited the desert or mountain habitats of the modern species.</p><p>As in Europe, the only true <b>ruminants</b> of the time in North America were small hornless animals loosely resembling musk deer. The exact relationship of these animals to other ruminants is unclear; they may well represent a side branch with no close modern relatives. <i>Hypertragulus</i> is a typical example, with most other primitive North American ruminants being placed in its family. They were small creatures, only weighing around 3-4 kg (7-9 lbs) and had several features that place them amongst the most primitive of all ruminant animals.</p><p>Many of these features are highly technical, but they include a relatively short snout with a tusklike premolar tooth in the lower jaw separated from the teeth to either side by a distinct gap. They still had the full set of five toes on the front feet, although those at the sides were reduced so that most of the weight would have been taken on those forming the modern "cloven hoof"; the hind feet had just four toes each and closer to what we would see today in living ruminants such as deer. </p><p>Once included in the same family, <i>Leptomeryx</i> is now split off into its own group but would, in life, have looked superficially quite similar. Distinguishing features include the lack of tusks - indeed, the equivalent tooth is unusually small and vestigial - and the presence of only four toes on the front feet. It's another animal that survived from earlier times, although the species do become <a href="https://www.proquest.com/openview/bcd21e3fa576dec93ab8fbba9f478c5e/1?pq-origsite=gscholar&cbl=18750" target="_blank">smaller</a> after the climatic shift of the Early Miocene. Although less diverse than the hypertragulids, the leptomerycids as a whole survived longer, making it into the Miocene before <i>Leptomeryx</i>'s last descendant died out. </p><p><i>Leptomeryx</i> species also developed more complex teeth, with a <a href="https://doi.org/10.2110/palo.2009.p09-156r" target="_blank">larger grinding surface</a>, in the Oligocene compared with those of their earliest forms, perhaps because the drier climate favoured tougher plants. Nonetheless, compared with modern ruminants, the <a href="https://www.proquest.com/openview/c7efad5c7cb910cb1acd14dd9af71a3e/1?pq-origsite=gscholar&cbl=18750" target="_blank">teeth</a> of both hypertragulids and lepotmerycids were primitive and do not seem as suited to a purely herbivorous diet as we might expect. They likely fed on soft leaves, some fruit, and perhaps even insects. One study based on isotope analysis suggests that, despite their skeletal affinities to modern ruminants, they had <a href="https://doi.org/10.1016/j.palaeo.2007.08.007" target="_blank">not yet developed</a> the full ruminating digestive system and would likely have been less efficient at processing tough plant matter than their later relatives.</p><p>These animals were unique to North America, although <i>Leptomeryx</i> is similar enough to an animal living in India at the time that the latter was <a href="https://www.jstor.org/stable/24094319" target="_blank">once considered</a> synonymous, suggesting that its ancestors may have been Asian. However, they were not the only cloven-footed mammals in North America at the time, since the continent was also home to others that were either unique or that had close relatives elsewhere. Next time, I will be looking at some of those.</p><p><i>[Photos by "<a href="https://commons.wikimedia.org/wiki/User:Ghedoghedo" target="_blank">ghedoghedo</a>" and "<a href="https://www.flickr.com/photos/47573122@N05" target="_blank">inazakira</a>", from Wikimedia Commons.]</i></p>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com0tag:blogger.com,1999:blog-4209921721314660731.post-29238596475604279082023-12-03T16:37:00.000+00:002023-12-03T16:37:11.822+00:00The Other One: Red Pandas<div class="separator"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh4swIdjpRc45nmOA8UQqgVQpLWyV3sPaWtskH-IjwUa240WmnUbXhznPaskda2jJMy_M_DWw3mxtC2mvL0oOy0Ar0HjwEPhBauJA_XvdqZh27GKvmv51jmTNq554_4Uw7X1tppxrkCIu9HHdBAoPIAid8lHCrpxO7bjf0kKZm-3-MNNmjxC75i0giLvJSE/s400/Red_Panda_-_52301611571.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em; text-align: center;"><img border="0" data-original-height="319" data-original-width="400" height="255" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh4swIdjpRc45nmOA8UQqgVQpLWyV3sPaWtskH-IjwUa240WmnUbXhznPaskda2jJMy_M_DWw3mxtC2mvL0oOy0Ar0HjwEPhBauJA_XvdqZh27GKvmv51jmTNq554_4Uw7X1tppxrkCIu9HHdBAoPIAid8lHCrpxO7bjf0kKZm-3-MNNmjxC75i0giLvJSE/s320/Red_Panda_-_52301611571.jpg" width="320" /></a></div>Over the course of this year, I have looked at all the species of the <a href="https://synapsida.blogspot.com/search/label/raccoon%20family" target="_blank">raccoon</a> and <a href="https://synapsida.blogspot.com/search/label/skunk%20family" target="_blank">skunk</a> families, two groups of smallish carnivorous mammals that are mostly confined to the Americas. These two families are themselves related, forming part of a larger group called the "musteloids", traditionally ranked as a "superfamily". The group is named for a third family within it, the mustelids or "<a href="https://synapsida.blogspot.com/search/label/Weasel%20family" target="_blank">weasel family</a>", which contains a much wider - and more widespread - group of species, including otters, badgers, and wolverines. <div><br /></div><div>The musteloid superfamily, however, also contains one other living species that does not fit into any of the three main families: the <b>red panda</b> (<i>Ailurus fulgens</i>). Six years ago, I <a href="https://synapsida.blogspot.com/2017/05/just-what-is-red-panda-anyway.html" target="_blank">took a look</a> at the history of Western knowledge of this animal, and of how it relates to other mammal families. The upshot of that, you may recall, is that there is broad agreement that the red panda is the only living species in its family, distinct from raccoons, skunks, and weasels although quite how was unclear. Since I wrote that, a <a href="https://doi.org/10.1093/sysbio/syx047" target="_blank">further study</a> has come out supporting the evolutionary tree I described as "the current best bet", but I'd be remiss if I didn't point out that <a href="https://doi.org/10.1371/journal.pone.0240770" target="_blank">at least one</a> contradictory study has also been published. It's perhaps fair to say that the four families of musteloids all appeared fairly suddenly at around the same time (<a href="https://doi.org/10.1016/j.ympev.2009.08.019" target="_blank">likely</a> around the <a href="https://synapsida.blogspot.com/2023/05/oligocene-pt-2-europes-big-break.html" target="_blank">Grande Coupure</a>) and the exact sequence of events is difficult to disentangle.<span><a name='more'></a></span></div><div><div class="separator" style="clear: both; text-align: center;"><br /></div>This time, however, I want to take more of a look at the animal itself, given that I've now done the same for every other musteloid species.</div><div><br /></div><div>The red panda was first scientifically described in 1825, over forty years before the (not closely related) giant panda. At the time, it was placed in the then-recently named raccoon subfamily of bears. In 1843, John Edward Gray separated them out from the raccoons, creating the red panda family for that one species alone. Initially, he considered them, like the raccoons, to be a subfamily of bears, because they walk on the soles of their feet as bears do, but, of course, that particular scheme no longer holds.</div><div><br /></div><div>Red pandas do, superficially, look a lot like raccoons. They are about the same size and have a bushy red tail with red-and-white stripes that look remarkably raccoon-like. They are generally reddish in colour, but with black fur on the legs and white markings on the face that, again, resemble the masks on many raccoon species. Look closer, however, and there are some significant differences.</div><div><br /></div><div>The teeth of red pandas follow the same general pattern of other musteloids, with a row of clipping incisor teeth followed by a single canine and then five or six cheek teeth in each side of each jaw. However, the canines are unusually small for a carnivoran and the cheek teeth are much broader and flatter than in any of their relatives, forming a wide and relatively complex grinding surface that's better suited to chewing up tough plant matter than for slicing meat. These entirely replace the long <a href="https://synapsida.blogspot.com/2010/12/carnivores-carnivorans-and-carnassials.html" target="_blank">carnassial</a> blade that carnivorans normally have and are an indication of their specialised diet.</div><div><br /></div><div>Another unusual adaptation is the elongation of the radial sesamoid bone. This is not a bone found in regular human anatomy, although it is found in some other mammal species, notably including carnivorans. It is essentially an extra wrist bone that forms within a tendon just below the base of the thumb, and probably does little more than help support body weight in other animals. Even in the red panda, it is not especially large (just larger than it normally would be) but it does <a href="https://doi.org/10.1111/j.1469-7580.2006.00649.x" target="_blank">articulate</a> with the rest of the wrist and is attached to the musculature, allowing it some degree of movement. </div><div><br /></div><div>It's <a href="https://doi.org/10.1111/j.1469-7580.2006.00649.x" target="_blank">not quite</a> the fully-developed "second thumb" of giant pandas, but it does at least allow the animal an improved ability to grip bamboo shoots. And this, of course, relates again to the diet of red pandas, <a href="https://doi.org/10.4404/hystrix-25.1-9033" target="_blank">80 to 90%</a> of which consists of bamboo. The remainder is formed of <a href="https://doi.org/10.4098/j.at.0001-7051.017.2008" target="_blank">fruits</a>, buds, <a href="https://www.researchgate.net/profile/Achyut-Aryal/publication/258515861_Summer_Diet_and_Distribution_of_the_Red_Panda_Ailurus_fulgens_fulgens_in_Dhorpatan_Hunting_Reserve_Nepal/links/00b49528c53254a89b000000/Summer-Diet-and-Distribution-of-the-Red-Panda-Ailurus-fulgens-fulgens-in-Dhorpatan-Hunting-Reserve-Nepal.pdf" target="_blank">lichen</a>, and other easily digestible plant matter, and occasionally things like bird eggs. Bamboo is, however, not very nutritious, and red pandas <a href="https://doi.org/10.1002/(SICI)1098-2361(2000)19:1%3C27::AID-ZOO3%3E3.0.CO;2-9" target="_blank">lack</a> the anatomical adaptations that hoofed mammals do to fully digest tough plant matter. They partly get around this by carefully selecting the best species of bamboo, and feeding primarily on tender new shoots and leaves, but even so they need to eat pretty much <a href="https://doi.org/10.1111/j.1469-7998.1999.tb01053.x" target="_blank">their own body weight</a> in food each day.</div><div><br /></div><div>This dietary specialisation goes a long way to explaining why red pandas also have a narrow preference for habitat. They inhabit densely forested terrain from 1500-4500 metres (5,000-15,000 feet) in elevation, <a href="https://doi.org/10.1016/S0006-3207(00)00079-3" target="_blank">preferring</a> places that not only have plentiful bamboo but a thick tree canopy and lots of <a href="https://doi.org/10.1016/j.biocon.2018.02.014" target="_blank">fallen logs</a> and low-lying shrub that make it easier to access their preferred food. They also prefer south-facing slopes, presumably for the warmth and are only common on slopes of over 45% in places where smoother terrain is <a href="https://doi.org/10.1644/1545-1542(2000)081%3C0448:HUASBT%3E2.0.CO;2" target="_blank">occupied</a> by giant pandas. </div><div><br /></div><div>This restricts them to the southern side of the Himalayas and associated mountain ranges. Two <a href="https://doi.org/10.1016/j.ympev.2004.12.016" target="_blank">subspecies</a> are recognised, and there has been some debate recently as to whether they should be considered entirely <a href="https://doi.org/10.1126%2Fsciadv.aax5751" target="_blank">different species</a>. The more widespread of the two lives from Nepal in the west along the mountain range as far as China, passing through Bhutan, northeast India and the extreme north of Myanmar on the way. The second is restricted to China, in the Hengduan Mountains of western Sechuan and Yunnan provinces. </div><div><br /></div><div>Red pandas sleep during the full light of the day, curling up on a high tree branch or stretching out, cat-like, if the weather is too hot. They are active during the twilight hours as well as during the night proper, and are mostly solitary, scent marking their territory using middens to defecate in as well as using the glands on their paws and at the base of the tail. They are not, however, aggressive towards one another, presumably staying well away when they find another red panda has scent-marked an area.</div><div><br /></div><div>The mating season runs from January to early March, so that the young are born between June and July. Litters are small, with just two young being most common, although they can vary from single births up to four. As in many other carnivores, the young are born blind and helpless, opening their eyes at around day 18. They reach sexual maturity in their <a href="https://doi.org/10.1111/j.1469-7998.1979.tb03402.x" target="_blank">second year</a>.</div><div><br /></div><div>The amount of forest loss across their range, and their <a href="https://doi.org/10.1017/S0030605316000399" target="_blank">dislike</a> of agricultural land even when it includes bamboo, makes it obvious that their overall population must be in decline, but accurate population estimates are lacking, so we don't know quite how fast this is happening. They are also hunted, as much for the pet trade as for their fur or meat and suffer <a href="https://doi.org/10.1016/0006-3207(91)90104-H" target="_blank">high infant mortality</a> where humans and dogs are common. As a consequence of this, and because of their distinctive nature as the only living member of their family, they are internationally listed as an endangered species as a precautionary measure.</div><div><br /></div><div>However, while the family may contain only one living species, it does have more of a fossil record than that might lead one to believe. Several fossil species are known, although most of them from only very fragmentary remains - in some cases, a single tooth. The closest known relative of the living species is probably <i>Parailurus</i>, which is known from places as far afield as <a href="https://www.researchgate.net/publication/279558711_Pliocene_Carnivores_Carnivora_Mammalia_from_Ivanovce_and_Hajnacka_Slovakia" target="_blank">Slovakia</a> and <a href="https://doi.org/10.1671/2441-14" target="_blank">Japan</a>, taking central <a href="https://doi.org/10.1134/S1028334X11050357" target="_blank">Asia</a> along the way. It seems to have been very similar to the modern species, except for being about 50% larger, and probably more omnivorous, and must also have been more adaptable given that such a wide area cannot have been entirely covered in high-altitude stands of bamboo.</div><div><br /></div><div><i>Parailurus</i> lived not long before the Ice Ages, alongside many other species of the family, showing that, while they were never exactly diverse, they were at least once more so than they are today. The best-preserved fossil of the family is not much older, at around 5 million years, and was <a href="https://doc.rero.ch/record/13466/files/PAL_E141.pdf" target="_blank">discovered</a> in, of all places, Tennessee. This is <i>Pristinailurus</i>, and there are sufficient remains to determine that it was only more omnivorous than even <i>Parailurus</i>, but also that it would have been able to <a href="https://www.researchgate.net/profile/Lauren-Lyon-3/publication/308778674_ANATOMICAL_COMPARISON_OF_THE_POSTCRANIAL_SKELETON_OF_THE_EXTANT_RED_PANDA_AILURUS_FULGENS_TO_THE_EXTINCT_LATE_MIOCENE_AILURIDS_SIMOCYON_BATALLERI_AND_PRISTINAILURUS_BRISTOLI_CARNIVORA_AILURIDAE/links/5820da6708aeccc08af663e3/ANATOMICAL-COMPARISON-OF-THE-POSTCRANIAL-SKELETON-OF-THE-EXTANT-RED-PANDA-AILURUS-FULGENS-TO-THE-EXTINCT-LATE-MIOCENE-AILURIDS-SIMOCYON-BATALLERI-AND-PRISTINAILURUS-BRISTOLI-CARNIVORA-AILURIDAE.pdf" target="_blank">climb trees</a> without difficulty, perhaps feeding on their leaves as well as seeking shelter. </div><div><br /></div><div>This would, however, have lived alongside the much larger <i>Simocyon</i>, which is best known from Spain, but has also been discovered in both <a href="https://doi.org/10.1080/02724634.1997.10010963" target="_blank">China</a> and <a href="https://www.academia.edu/download/31452338/Tedrow__A.__J._A._Baskin__and_S._F._Robison._1999._An_additional_occurrence_of_the_genus_Simocyon_(Mammalia__Carnivora__Procyonidae)_in_.pdf" target="_blank">North America</a>. This was a puma-sized animal with <a href="http://app.pan.pl/acta50/app50" target="_blank">teeth</a> that indicate a diet that was still almost entirely carnivorous. Significantly, it <a href="https://doi.org/10.1073%2Fpnas.0504899102" target="_blank">already had</a> the expanded sesamoid bone that modern red pandas use to grip onto bamboo, showing that this must have originally evolved for a different purpose. The most likely explanation is that it helped the animal to climb, perhaps initially to escape larger predators and then as more of a lifestyle choice, before it became co-opted for feeding.</div><div><br /></div><div>The oldest known fossil species currently assigned to the family are those belonging to <i>Amphictis</i>, which lived across much of the Northern Hemisphere in various different forms, and are thought to have been fairly typical small carnivores for their time. The oldest ones lived around 30 million years ago, not long after molecular estimates suggest that the family first originated in a rapid burst of diversification that split from the first skunks, raccoons, and weasels.</div><div><br /></div><div><i>[Photo by <a href="https://www.flickr.com/photos/mathiasappel/52301611571/" target="_blank">Mathias Appel</a>, from Wikimedia Commons.]</i></div>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com2tag:blogger.com,1999:blog-4209921721314660731.post-7733223531022254952023-11-25T16:53:00.002+00:002023-11-25T22:04:48.208+00:00The First Whales to Use Sonar?<p></p><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody><tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi9pk0za4VWNCRyTUaj3qOrnoZl-zTkMwrzB08bCAzRYLyqp8W1oBZuuZrNb1kiOjxPayQKX7uL0ePRHblF-TZiHzrhpT7dKlUgXpOyDOsVFkqYosLRebI2nkt8L-peg3A7QWEPG5aCJ0Dq9wcHyMJQLcQY19vN2o8ASozzko6MwEIA7PNorIG0hgpie0bZ/s400/xenorophus.jpg" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="386" data-original-width="400" height="309" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi9pk0za4VWNCRyTUaj3qOrnoZl-zTkMwrzB08bCAzRYLyqp8W1oBZuuZrNb1kiOjxPayQKX7uL0ePRHblF-TZiHzrhpT7dKlUgXpOyDOsVFkqYosLRebI2nkt8L-peg3A7QWEPG5aCJ0Dq9wcHyMJQLcQY19vN2o8ASozzko6MwEIA7PNorIG0hgpie0bZ/s320/xenorophus.jpg" width="320" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;"><i>Xenorophus</i></td></tr></tbody></table>Other than their obvious physical adaptations, one of the most familiar features of dolphins and whales is their ability to use ultrasound to echolocate. All dolphins, porpoises, and toothed whales (collectively called <b>odontocetes</b>) can echolocate and, while some of the fine details do vary between, say, sperm whales and some of the smaller species, the basic mechanism is much the same. Ultrasound would not have been useful to the large, ground-dwelling ancestors of whales in the same way that it is for bats, so it must have evolved after they entered the water. But how soon after?<p></p><p>We can put some limits on this. At the younger end, since all odontocetes echolocate, it's unlikely to have evolved any later than their last common ancestor, which is estimated to have lived around 34 million years ago. On the other hand, it's notable that the toothless, baleen, whales do not use ultrasound; in fact, they are specialised in the exact opposite direction to produce sounds well below, not above, the range of human hearing. This suggests that they evolved along different lines, and that the origins of ultrasonic echolocation lie somewhere after the two split. <span></span></p><a name='more'></a><p></p><p>Whether an animal uses ultrasound is, as one might expect, not all that easy to tell when all you have to go on is a skeleton, and often one that's incomplete or badly damaged at that. Many of the <a href="https://doi.org/10.1002/(SICI)1097-4687(199606)228:3%3C223::AID-JMOR1%3E3.0.CO;2-3" target="_blank">adaptations</a> required to produce ultrasound lie in the soft tissues... but not, as it happens, all of them. Crucially, such animals need air gaps around the ear to stop sound being transmitted from the skull and confusing directional hearing, and a concave shape to the bones under the forehead, leaving space for the melon that transmits the outgoing signal.</p><p>If those features are both present in a fossil, it's a fair bet that the animal in question could use ultrasound to echolocate. Thus, for instance, we can be confident that the very earliest whales, while they may have had directional underwater hearing, did not yet have ultrasound. It's something odontocetes evolved, not something that baleen whales lost.</p><p>In 1923, Remington Kellogg published a <a href="https://repository.si.edu/bitstream/handle/10088/23638/SMC_76_Kellogg_1923_7_1-7.pdf" target="_blank">description</a> of a "dolphin" skull recovered from a deposit in South Carolina that we now know to have been around 28 million years old. He named it <i>Xenorophus</i>, for reasons that he didn't bother to explain ("<i>xeno</i>" means "strange", but what, if anything, "<i>rophus</i>" was intended to mean is unclear). Although it was obvious that this was an early odontocete, quite where it fit in relation to other whales was unclear and it ended up being shifted around quite a bit. It wasn't until 1972 that a second specimen was found but, after that, excavation of fossil beds in the area picked up and it became clear by at least <a href="https://doi.org/10.1017/S2475262200003403" target="_blank">1992</a> that it was merely one member of a group of similar animals. All of which, incidentally, have been found in the same small area of the southeastern US coast and (so far as we can tell) never spread to the other side of the Atlantic, let alone into other oceans.</p><p>In 2008, Mark Uhen <a href="https://doi.org/10.1017/S1477201908002472" target="_blank">officially named</a> that group as the Xenorophidae. At the time, it included <i>Xenorophus</i> itself, <i>Archaeodelphis</i>, which had actually been discovered slightly earlier, in 1921, and Uhen's newly described <i>Albertocetus</i>. Since then, five further genera have been added to the <b>xenorophids</b>, suggesting a group that was reasonably common and diverse, and that may be significant in cetacean evolution.</p><p>A <a href="https://doi.org/10.3390/d15111154" target="_blank">new analysis</a> of <i>Xenorophus</i> fossils, including a recently uncovered one that was unusually complete was published earlier this week, expanding on what we already knew about these animals. For example, while it is difficult to estimate the overall size of a cetacean from the skull alone, since bodily proportions varies more than it does amongst say, cats, here there's enough that the authors estimate that the animal would have between 2.6 and 3 metres (8½ and 10 feet) in length. </p><p>The shape and wear of the teeth suggest that, as in modern odontocetes, the teeth did not grind against one another as they do in most land mammals, and that the diet of <i>Xenorophus</i> was unusually variable - mostly regular fish, but with some individuals feeding primarily on either soft-bodied squid or tougher food items such as small sharks. The snout is relatively long, similar to that of a modern spinner dolphin and thus proportionately longer than some other odontocetes, and one juvenile fossil indicates that this shape appeared earlier in life than we might think. This suggests rapid strikes to snap at fish, using the teeth to piece and hold them. This is perhaps unsurprising, but it's worth noting that another member of the family, <i>Inermorostrum</i>, had <a href="https://doi.org/10.1098/rspb.2017.0531" target="_blank">no teeth at all</a>, presumably feeding on squid by simply sucking them out of the water. So feeding styles had diversified surprisingly early on in whale evolution, even among such a small and localised group.</p><p>Despite these similarities with modern dolphins, <i>Xenorophus</i> also shows several primitive features. The teeth are not all identical in shape, the bones of the snout are differently arranged, the anchor for the jaw muscles suggests a more powerful, but less rapid bite, and so on. But, bringing us back to the topic at the start of this post, there is good reason to suppose that it could use ultrasound to echolocate. This evidence comes from the new specimen, identified as belonging to a different species of the same genus as earlier ones and includes the fact that it did have the air sinuses that odontocetes need to home in on the sound of their sonar pings returning. </p><p>Similarly, the skull shows the asymmetric pattern seen in living whales that is thought to be associated with their <a href="https://doi.org/10.1073/pnas.1108927108" target="_blank">directional hearing</a>, and there is a small hole in the skull that matches one seen only in odontocetes, and through which the nerve to the melon and its <a href="https://doi.org/10.1088/1748-3182/3/1/016001" target="_blank">surrounding structures</a> passes. This fits with what we already knew of another xenorophid, <i>Echovenator</i>, which clearly <a href="https://doi.org/10.1016%2Fj.cub.2016.06.004" target="_blank">has the structures</a> required to hear ultrasound, including fine structures of the inner ear that (since they're on the inside of the bone) have yet to be examined in <i>Xenorophus</i> itself.</p><p>This, and other features, such as the number and size of the teeth, imply rapid evolution at the very base of the odontocete family tree, making them look quite different to their older, non-echolocating, ancestors after a relatively short period of time. Yet there are also several differences, suggesting that the xenorophids are a very early branch among the odontocetes, splitting off before the last common ancestor of all living species - which, in turn, means that they left no descendants. </p><p>That may not be terribly surprising, given how early they lived. But the apparently simple picture is confused by the <a href="https://doi.org/10.1080%2F02724634.2017.1366916" target="_blank">2017 discovery</a> of the fossil whale <i>Olympicetus</i> from Washington state. While this has no living descendants either, it has several features that suggest it is closer to the living odontocetes than it is to the xenorophids - its ancestor split off before theirs did. Which wouldn't be odd... except that examination of its inner ear revealed that it <a href="https://doi.org/10.1098/rsbl.2019.0083" target="_blank">couldn't hear ultrasound</a>. </p><p>Of course, it's possible that it had somehow lost the ability. But why would it do that? A more likely explanation is that it, and its common ancestor with the xenorophids, already had the directional hearing adaptations that are a prerequisite for sonar, but hadn't yet developed the full suite. In which case, the xenorophids must have developed ultrasound independently - the feature evolved twice. </p><p>The xenorophids did not last long, dying out at the end of the Oligocene 23 million years ago. By which time, the ancestors of all living odontocetes also had the same ability. But there seems to have been a time, very early on, when two different groups of whale both adapted their pre-existing abilities at directional hearing to do something entirely new for marine mammals and shared the same oceans.</p><p><i>[Illustration from <a href="https://doi.org/10.1098/rsbl.2019.0083" target="_blank">Boessenecker and Geisler 2017</a>, available under <a href="https://creativecommons.org/licenses/by/4.0/" target="_blank">CC-BY-4.0</a> license.]</i></p>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com0tag:blogger.com,1999:blog-4209921721314660731.post-29930106411301460562023-11-19T17:16:00.000+00:002023-11-19T17:16:12.419+00:00Learning to Hunt at Sea<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi0UJVqTU8hpdrP9nMsTts7es68TMPKLOBGGWspZv6oevtLuIJic2QB9YTHVwirXk8TzVJ6rV64pFTU8e4Eg3RPfaP1NmAkR5qBHjLvsw0svtCE4BfX8gkWQ9_uLDb4_YsiwTs6qfNaQ6JK1LbEk1IOlAl0OEaRrpkkr85nk4qaechyphenhyphenaneb7GDlnhGIfFkP/s400/Grey_Seal_-_Farne_Is_-_FJ0A6734_(35938100940).jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="326" data-original-width="400" height="261" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi0UJVqTU8hpdrP9nMsTts7es68TMPKLOBGGWspZv6oevtLuIJic2QB9YTHVwirXk8TzVJ6rV64pFTU8e4Eg3RPfaP1NmAkR5qBHjLvsw0svtCE4BfX8gkWQ9_uLDb4_YsiwTs6qfNaQ6JK1LbEk1IOlAl0OEaRrpkkr85nk4qaechyphenhyphenaneb7GDlnhGIfFkP/s320/Grey_Seal_-_Farne_Is_-_FJ0A6734_(35938100940).jpg" width="320" /></a></div>One of the distinguishing features of mammals is that they invest a lot of time and effort in caring for their young. Of course, birds do this too, as do some other vertebrates, but the provision of milk is one of the key defining traits that's true of all living mammal species. (Probably most extinct ones, too, although it's hard to tell with the <i>very</i> early species). This means that newborn mammals are entirely dependent on their mothers in a way that the young of, say, most reptiles are not. <p></p><p>But there comes a point where any mammal has to be weaned and make its way in the wider world. Even then, the maternal investment doesn't necessarily end with the mother continuing to raise and train her offspring for what can be an extended period. Brown bears, for example, are weaned at around six months, but they commonly stay with their mothers for at least another year, and often for <a href="https://doi.org/10.1007/s00265-003-0638-8" target="_blank">two or more</a>. We can see similar patterns in other mammals including, perhaps most obviously, primates.<span></span></p><a name='more'></a><p></p><p>In others, however, once the young are weaned, they're basically shoved out to fend for themselves. This is most common with small, fast-breeding mammals, such as mice. Perhaps the most extreme example comes from certain small marsupials, such as the antechinus, where raising children requires so much effort that the mother literally <a href="https://synapsida.blogspot.com/2011/01/have-children-and-die.html" target="_blank">drops dead</a> from exhaustion as soon as her young leave home. However, a similar "not my problem any more" approach is seen in some larger species, too.</p><p>Among these are seals and sea lions. The problem here is that baby seals can't swim, and even if they could, their fluffy white coats wouldn't insulate them in the water, so they'd soon die of hypothermia. But they have those fluffy coats because they need something to keep them warm on land while they build up their fat reserves to develop the blubber their parents have. Until then, their mother has to stay with them on land to protect them, which means that, until they're weaned, she isn't getting any food at all. </p><p>Understandably, as soon as her young are old enough not to need her milk, mum is going straight back to sea to gorge herself as much as she can before she dies of starvation. That leaves her with no time to make any further investment in her children, and they're just going to have to manage on their own. (Outside of the mammal world, we see something rather similar with <a href="https://doi.org/10.1098/rsbl.2016.0490" target="_blank">penguins</a>).</p><p>But what about those children? They have to teach themselves how, what, and where to hunt, all without any kind of guidance. And they'd better learn quickly, because they need to build up their weight and physical fitness before sharks or killer whales try to eat them. It's a very risky time of life for them, and there's obviously a strong evolutionary pressure on them to know what they're doing as soon as possible.</p><p>I've discussed grey seals (<i>Halichoerus grypus</i>) before as part of my 2017 series on seals. They're one of the larger species, found off both the northern coasts of Europe and off the northeast coast of North America. Although some use ice floes, they're typically born on rocky shores, and, like other seals, they bulk up very rapidly after birth. They're weaned at just 17 days old, at which point their mother makes the mad dash back to the sea to finally get something to eat. </p><p>By this point, the young seal may have nearly half of their body weight composed of fat, which you'd think would be enough blubber to insulate them. But now they've got another problem, because 17 days is just <a href="https://doi.org/10.1086/432922" target="_blank">not long enough</a> for them to develop the ability to store oxygen in their muscles when they dive. Add that to the fact that, being smaller, they have a higher metabolic rate than adults, and they just can't dive for long enough to feed. So they end up hanging around on land for something like a further <a href="https://doi.org/10.1086/528777" target="_blank">three weeks</a> before putting their flippers in the water.</p><p>But what happens once they do? Without any parental guidance, such as many other carnivores would receive, how do they learn what's good to eat and where to find it? Some of this is clearly going to be instinctive - for instance, they obviously know that food is out there in the sea somewhere, and not inland - but they can't start out immediately hunting as adults would, because they still aren't physically capable of holding their breath for that long. How that <a href="https://doi.org/10.1139/z99-022" target="_blank">changes</a> physiologically is something we know a bit about for various seal species, but how it affects their behaviour is (if <a href="https://doi.org/10.1186/s40462-016-0090-9" target="_blank">not a total mystery</a>) not so well studied.</p><p>What is probably the world's largest breeding population of grey seals is that on <a href="https://www.google.co.uk/maps/@44.0178687,-60.1572922,271896m/data=!3m1!1e3?entry=ttu" target="_blank">Sable Island</a>, a 43 km (27 mile) long sandspit about 175 km (110 miles) off the south coast of Nova Scotia. It's estimated that <a href="https://doi.org/10.1111/mms.12773" target="_blank">87,500</a> grey seals were born here in 2016 - around 80% of all the grey seals born in the northwest Atlantic (there are harbour seals, too, so at the right time of year the island is pretty busy for something that's basically just sand and marram grass). In that same year, 25 of the newly weaned grey seals were fitted with <a href="https://wildlifecomputers.com/taxa/pinniped/" target="_blank">satellite tracking transmitters</a> and then released to see what they did and where they went over the two to six months it took for the batteries to run flat.</p><p>Two of the transmitters failed before the seal pups even entered the sea, but those that were still working showed that almost all of the seals initially swam to the waters south of the island. The authors speculate that this might be due to the more gradual slope of the seafloor in that direction, making it easier to orient themselves, assisted by the sudden appearance of the deepwater current over the continental slope beyond it, marking the start of the deep ocean depths. But, in all honesty, that's just a guess. It's worth noting however, that some <a href="https://doi.org/10.1046/j.0021-8790.2001.00576.x" target="_blank">other seal species</a> also show a marked preference for a particular first direction of travel, influenced by the local geography. </p><p>After that, the young seals moved on to explore the surrounding shallow waters across the region south of Nova Scotia. Nonetheless, all of them went on to spend at least some time in much deeper waters beyond the continental shelf, with some going on to explore the deepwater Laurentian Channel between Nova Scotia and Newfoundland. One went the opposite direction, spending some time in the Gulf of Maine and in the shallow waters around Cape Cod and Nantucket.</p><p>In fact, over the months of the study, the young seals travelled much further than adults would over the same period. Adults are more inclined to find somewhere where food is plentiful and spend a lot of time there, diving repeatedly before eventually heading back to land for a rest. But these seals did not, suggesting that what was most important to them was exploring their neighbourhood and learning what was out there. In fact, the older they became, the less of this exploring they did, moving towards the adult behaviour of more thoroughly investigating a particular area where they already felt comfortable rather than seeking out pastures new.</p><p>Moreover, those seals whose wanderings led them to the shallowest sea banks that are still remote from land (such as, say, the Banquereau Bank about 100 km [62 miles] northeast of Sable Island) tended to stick around and explore less. This is the <a href="https://doi.org/10.1186/s40462-020-00225-7" target="_blank">sort of place</a> that many adults feed, so they'd probably hit it lucky and found a good place on an early trip. Similar refinement of search patterns is seen in other sea-feeding animals, including birds such as <a href="https://doi.org/10.1111/1365-2656.13044" target="_blank">shearwaters</a>.</p><p>Although most of them explored deep water seas, it was clear that they didn't like them, and they turned round again not long after reaching them. For instance, those that reached the Laurentian Channel never crossed it, heading back south when they realised how wide it was. In waters over 200 metres (660 feet) deep even adults wouldn't be able to reach the bottom, where there is not only more easily available prey, but possible <a href="https://doi.org/10.3389/fmars.2022.818635" target="_blank">subsurface features</a> that allow them to navigate. For grey seals, deep water is not a good place to be, and while the young pups clearly didn't know where it was until they got there, it wasn't somewhere they wanted to stay.</p><p>For all that they are presumably less physically resilient than older animals and have difficulty diving to similar depths, the young seals spent longer at sea than adults would - on average about nine or ten days at a time - and then spent longer recovering once they had returned to dry land. This probably reflects their inexperience. The whole point of swimming out to sea is to find food, but if you're not very good at catching it, or knowing the best places to dive to find it, you may have to spend <a href="https://doi.org/10.1098/rsbl.2007.0157" target="_blank">longer travelling</a> before you no longer feel hungry. That they spent some of their time travelling to places that, in retrospect, weren't good places to feed supports this; they just hadn't figured out what they were doing yet. </p><p>For many, this doesn't work out. Only around a third of grey seals survive long enough to breed, and it's likely that mortality is highest amongst the youngest individuals. But they have to learn somehow, because their parents won't help them; they can't even follow them to see where they go, because they've leave the short much earlier and, in any event, probably dive in places too deep for the youngsters to manage. But, even over the six months of this study, it was apparent that, week after week, the seal pups got steadily better, making shorter, more effective, trips and gradually figuring out how to get the food that their parents won't teach them about.</p><p><i>[Photo by <a href="https://www.flickr.com/people/30818542@N04" target="_blank">Francesco Veronesi</a>, from Wikimedia Commons.]</i></p>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com0tag:blogger.com,1999:blog-4209921721314660731.post-78781140208905597272023-11-12T16:11:00.001+00:002023-11-12T16:11:47.310+00:00Defending the Troops<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh6QseDJUjYR72rAdqze4Pw7Ro2hnFF0koV76KRzD_ftCIq5xBoypkp3aIxyS59nCbYXXcS_qAPTVAvaDvOfi0OGqS9VXERY1_zxLaR_U0ElLZ4PCjmAxBnDIn1hm-yYDLC8m4N_1YEWZ6POGxmyRM_HlUJOKkh9_h9GDRt5h6ikc07hahqxbzqGEZ9XStR/s509/Tarangire_2012_05_27_2034_(7468492726).jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="350" data-original-width="509" height="220" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh6QseDJUjYR72rAdqze4Pw7Ro2hnFF0koV76KRzD_ftCIq5xBoypkp3aIxyS59nCbYXXcS_qAPTVAvaDvOfi0OGqS9VXERY1_zxLaR_U0ElLZ4PCjmAxBnDIn1hm-yYDLC8m4N_1YEWZ6POGxmyRM_HlUJOKkh9_h9GDRt5h6ikc07hahqxbzqGEZ9XStR/s320/Tarangire_2012_05_27_2034_(7468492726).jpg" width="320" /></a></div>A <a href="https://synapsida.blogspot.com/2023/10/follow-leader.html" target="_blank">few weeks ago</a>, I talked about how group-living mammals decide when and where to move, and how their decision-making leadership is structured. But there are other aspects to how animals living in a herd or pack might travel, or, indeed, position themselves when they are not travelling. One of these is the perceived risk of predation. <p></p><p>It's well-known that predators will <a href="https://doi.org/10.2307/1938472" target="_blank">tend</a> to pick off <a href="https://doi.org/10.1098/rsbl.2009.0742" target="_blank">weaker</a> individuals if they can, largely to save themselves <a href="https://doi.org/10.1644/1545-1542(2000)081%3C0462:SOMDBM%3E2.0.CO;2" target="_blank">the effort</a> of capturing something that's more able to escape or fight back. But it's also likely that some positions within a herd are going to be inherently safer than others, and merely being fit may not help much if you're an obvious target. The question then arises as to whether certain sorts of individual are likely to occupy safer or more dangerous positions and as to how the group as a whole arranges itself.<span></span></p><a name='more'></a><p></p><p>However, which position in a herd is the most exposed may depend on what sort of predator it is that you're worried about. In the case of large mammalian predators, there are basically two different strategies that they use for capturing prey, and these have different implications for how herding herbivores might choose to defend themselves. Firstly, there are pursuit (or "coursing") predators, such as wolves, cheetahs, and hyenas, which will pursue their targets and try to outrun them. Here, the main factor that affects a prey animal's risk of being attacked is simply how close to the <a href="https://doi.org/10.1093/beheco/arr026" target="_blank">edge of the group</a> they happen to be. </p><p>Ambush predators, on the other hand, tend to sneak up on a group, relying on taking down their target almost immediately, and using cover to get as close as possible before doing so. Here, the primary risk is not being close to other prey animals - if the group is spread out, the ambush predator could manage to get well inside it without being spotted and <a href="https://doi.org/10.1093/beheco/arz197" target="_blank">strike without warning</a> at individuals <a href="https://doi.org/10.1016/S0003-3472(89)80143-5" target="_blank">nowhere near</a> the edge. In the case of large land mammals, the primary concerns here are cat-like predators such as leopards or tigers; for smaller ones, eagles or owls might be a bigger risk, since being in the middle of the group isn't going to help at all.</p><p>Another factor to consider is that there may be other reasons for taking up a particular position within a herd or other grouping. The dominant individuals, for instance, may tend to be <a href="https://doi.org/10.1016/j.anbehav.2016.07.011" target="_blank">at the centre</a>, where they can best take control of the group and see what most of their subordinates are up to. Or, then again, if the group is travelling, the dominant individuals may well be <a href="https://doi.org/10.1016/S0003-3472(84)80292-4" target="_blank">at the front</a>, leading the way. In that position, the chances of coming across an ambush predator unexpectedly are presumably at their highest, but, equally, it's the animals <a href="https://doi.org/10.1098/rstb.2016.0232" target="_blank">at the back</a> that have the most to fear from pursuit predators, which will likely figure that anything having difficulty keeping with their fellows is an ideal target.</p><p>Given all of these possible factors, it's unsurprising that studies of even how a single species gathers together have often been ambiguous or contradictory - a lot may depend on the <a href="https://doi.org/10.1016/j.biocon.2019.02.001" target="_blank">exact circumstances</a>. But this has not, of course, stopped researchers from trying to answer such questions.</p><p>A study <a href="https://doi.org/10.1371/journal.pone.0287357" target="_blank">published last week</a> looked at the grouping behaviour of <b>olive baboons</b> (<i>Papio anubis</i>) in Kenya, using GPS collars to avoid the risk of the animals changing their behaviour when they thought that humans were watching them (given that humans are, themselves, something that baboons are going to be <a href="https://doi.org/10.1038/s41598-022-12312-3" target="_blank">wary</a> of). The olive baboon is the most widespread of the six species of baboon, being found across a wide swathe of Africa just north of the equator, from Guinea in the west to Ethiopia in the east, taking in 24 other countries on the way. They live in large mixed-sex groups, sometimes of over a hundred members each, with a <a href="https://doi.org/10.1002/ajp.20967" target="_blank">complex social structure</a>, and their primary <a href="https://doi.org/10.1163/156853994X00488" target="_blank">predators</a> are leopards, lions, and spotted hyenas, in that order.</p><p>The baboon troop in question lives in a <a href="https://www.google.co.uk/maps/place/Mpala+Research+Centre/@0.2924197,36.8985067,47261m/data=!3m1!1e3!4m12!1m5!3m4!2zMMKwMjAnMDAuMCJOIDM2wrA1MCcwMC4wIkU!8m2!3d0.3333333!4d36.8333333!3m5!1s0x1787becf87583c4b:0x59a9fd674590a817!8m2!3d0.292366!4d36.8984604!16s%2Fg%2F1w0md_h1?entry=ttu" target="_blank">wide area</a> of scrubby bush near the <a href="https://mpala.org/" target="_blank">Mpala Research Centre</a> in Kenya and has been studied for various purposes since 2011. At the time of the study, it consisted of eight adult males, sixteen adult females, and 34 adolescents and infants. All three of the major predators of baboons also live in the area, although, at least in modern times, they are not very common and mostly focus on other local prey.</p><p>Tracking the movements of the group - or at least the 26 of its members that had been fitted with the GPS collars - showed that the adult males tended to position themselves at the outer edge of the troop, leaving themselves more exposed to any potential predators. This is not surprising, as we see a similar pattern in <a href="https://doi.org/10.1007/s10764-015-9818-4" target="_blank">vervet monkeys</a>, where males stay on the outer edge of a group even when it is stationary, and they aren't leading the way during travel. Indeed, we also see the same pattern of behaviour in other mammals, such as male <a href="https://doi.org/10.1016/S0003-3472(05)80984-4" target="_blank">gazelles</a>, which are, indeed, more often killed by cheetahs as a result.</p><p>Why would this be? There are at least three possibilities, and they are not mutually exclusive. One is that it's a simple trade-off, a consequence of the fact that the males of most mammalian species are larger than the females. In olive baboons, for example, the average adult male weighs about 24 kg (53 lbs), while a typical female weighs only 15 kg (32 lbs). Fully-grown males, therefore, need more food, and it's <a href="https://doi.org/10.1111/j.1469-185x.1994.tb01505.x" target="_blank">better for them</a> to forage at the edge of the group where there is less competition, even if it means that that puts them at greater risk.</p><p>But that may not be the only reason. Especially if the baboons are worried about pursuit predators, such as hyenas, it makes sense to have the biggest, strongest individuals at the outer edge of the group, so that they can <a href="https://doi.org/10.1007/BF00290902" target="_blank">protect</a> their more vulnerable troop-mates further in. Many of the youngest animals are likely to be their own children, which they naturally have an interest in protecting, but even <a href="https://doi.org/10.1007/s00265-009-0781-y" target="_blank">if they aren't</a>, no male is likely to want his potential mates to be killed, either. Such behaviour also makes it easier to look out for rival troops, whose males may want to take over their own.</p><p>The third possibility is related to the second: the males may simply be <a href="https://doi.org/10.1111/eth.13233" target="_blank">showing off</a>, proving their bravado and physical fitness by exposing themselves to danger in the hopes of impressing the females. Because some primates do that sort of thing.</p><p>But it's not just pursuit predators that male baboons put themselves at risk from. It would still be possible for males to be reasonably close to one another while staying at the edge of the group, assuming they didn't space themselves out evenly. But, in fact, in this group, they did space themselves out, while females and young were more likely to clump together, gaining protection in numbers from ambush predators that might sneak up on them. Being relatively isolated isn't going to help the males protect anyone else more effectively, although it would give them more access to food sources, and it fits with the "showing off" hypothesis, too. At least as likely, though, is that the adult males in a troop tend to be aggressive towards one another, since they are not close relatives (they will have been born outside the troop and moved in on their own, while the females stay living with their sisters).</p><p>It's all very well being exposed to predators, but the males would probably rather avoid being exposed to each other, too. There's no point <a href="https://doi.org/10.1163/156853996X00530" target="_blank">getting into a fight</a> if you don't have to.</p><p>The researchers expected that the dominant male in the troop would be the exception to these general rules. He shouldn't have to worry about other males pinching his food or otherwise trying to challenge him since, most of the time, they wouldn't dare. So staying in the middle of the group, where he can protect his children and have greater access to the adult females, makes a lot of sense. (Not even necessarily for the obvious reasons; male baboons will apparently leap to the defence of a female even if they don't expect <a href="https://doi.org/10.1007/s00265-009-0786-6" target="_blank">anything in return</a>). </p><p>But, in this case, that isn't what happened; the alpha male stayed near the edge of the troop, just like his subordinates. The researchers speculate that, since the dominant male in this group hadn't been alpha for long, he didn't yet have enough children to make it worth his while... but it's equally possible that our intuitions in this area may be wrong, even if they do seem to <a href="https://doi.org/10.1006/anbe.1996.0392" target="_blank">hold</a> for some other primate species.</p><p>Rank may have its privileges, but, in this one baboon troop at least, that doesn't include keeping yourself safe behind the front lines.</p><p><i>[Photo by <a href="https://www.flickr.com/people/10299779@N03" target="_blank">Harvey Barrison</a>, from Wikimedia Commons.]</i></p>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com1tag:blogger.com,1999:blog-4209921721314660731.post-2814432313424666052023-11-05T16:01:00.004+00:002023-11-05T17:33:35.395+00:00Skunks of the World: Stink Badgers!<p></p><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody><tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiEsq0ca0_trJwBEVUrCI_Pb97Ufg9LIz4gWq9qAJ-gGGXCScJOIol6_kWszvgmxF09Spa9FeP3vY_1KLPqDGBYuX1N2UlzjyJ9cN7yZhmmKUUN1CZ60zF2FM5IEifkHVlZsYbmnWsdFchHv4kBVoOicWYMBc3ihBASa0v1kRglVPbIkuWo0mJUAzUyxtsE/s400/800px-Mydaus_javanensis.jpg" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="268" data-original-width="400" height="214" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiEsq0ca0_trJwBEVUrCI_Pb97Ufg9LIz4gWq9qAJ-gGGXCScJOIol6_kWszvgmxF09Spa9FeP3vY_1KLPqDGBYuX1N2UlzjyJ9cN7yZhmmKUUN1CZ60zF2FM5IEifkHVlZsYbmnWsdFchHv4kBVoOicWYMBc3ihBASa0v1kRglVPbIkuWo0mJUAzUyxtsE/s320/800px-Mydaus_javanensis.jpg" width="320" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">Sunda stink badger</td></tr></tbody></table>As I mentioned at the <a href="https://synapsida.blogspot.com/2023/07/the-stinky-family-skunks.html" target="_blank">beginning of this series</a>, for most of the 20th century, skunks were thought to be mustelids, members of the same animal family as weasels, polecats, badgers, and the like. They were given their own family in the 1990s, once it became clear that racoons were more closely related to mustelids than they were. But the genetic analyses that revealed this fact also provided another surprise.<p></p><p>It had been assumed that skunks (as a subfamily of mustelids) lived only in the Americas, much as racoons do. But the genetic studies <a href="https://doi.org/10.1016/j.ympev.2010.01.033" target="_blank">showed</a> that two species of supposed badger living in Indonesia were not, in fact, badgers at all, but members of the newly erected skunk family. These animals are collectively known as "stink badgers", although the local name of "teludu" and "pantot" are sometimes preferred.<span></span></p><a name='more'></a><p></p><p>It might seem odd that we'd mistake a skunk for a badger, and in fact, the story isn't quite that simple. For one thing, when <a href="https://en.wikipedia.org/wiki/Anselme_Ga%C3%ABtan_Desmarest" target="_blank">Anselme Desmarest</a> first scientifically described the animal in his 1820 work on the mammals of the world, he identified it as a skunk, placing it in the same genus as the American animals. For another, at least <a href="https://doi.org/10.2307/1378960" target="_blank">one study</a> in the 1970s suggested that stink badgers might be closer to skunks than they were to other badgers. This was based on their brain anatomy, with skunks and stink badgers both having the parts of their brains dedicated to smell enlarged compared with "other" mustelids.</p><p>Set against this, we have the fact that skunks, so far as was known, were otherwise unique to the Americas, and that stink badgers don't really look much like them. While modern studies are unequivocal that, yes, they really are skunks, they split off from the other members of their family around <a href="https://www.jms.mabjournal.com/index.php/mab/article/view/1847" target="_blank">10 million years ago</a>, probably when the latter wandered across a land bridge into North America.</p><p><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEibjgALcpJDiHpWozNBrsHF2HLxffpgc3u1sIFT9EgU6NYJp-ZpROLCGtbFyIwhGUX56tVlhMKBxVnu0WqgL1x6su01a0qotfPj1KOqIemdkpVGD56gts567CuibI8XmdioDM4SiPue05Rz2ITy_cduuSSFxu-i-mbbYsprX2J9n6LSahzchIHUb4veGh6P/s400/Mephitidae.JPG" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em; text-align: center;"><img border="0" data-original-height="400" data-original-width="379" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEibjgALcpJDiHpWozNBrsHF2HLxffpgc3u1sIFT9EgU6NYJp-ZpROLCGtbFyIwhGUX56tVlhMKBxVnu0WqgL1x6su01a0qotfPj1KOqIemdkpVGD56gts567CuibI8XmdioDM4SiPue05Rz2ITy_cduuSSFxu-i-mbbYsprX2J9n6LSahzchIHUb4veGh6P/s320/Mephitidae.JPG" width="303" /></a>By far the more widespread of the two species is the one that Desmarest originally named, the <b>Sunda stink badger</b> (<i>Mydaus javanensis</i>). This is currently divided into three subspecies, one living in Sumatra and Java, one in Borneo, and the third on the Natuna Islands between Borneo and Peninsular Malaysia. Even today, it is apparently one of the <a href="https://www.researchgate.net/profile/Daishi-Higashide-2/publication/328303119_Camera-trap_records_of_Sunda_Stink-badger_Mydaus_javanensis_and_other_small_carnivores_in_South_Kalimantan_Indonesia/links/5bc54650299bf17a1c556499/Camera-trap-records-of-Sunda-Stink-badger-Mydaus-javanensis-and-other-small-carnivores-in-South-Kalimantan-Indonesia.pdf" target="_blank">most commonly seen</a> carnivorous mammals in these islands and hunting is sufficiently low-level (although not non-existent) that it does not appear to be under threat.</p><p>Having said that, especially compared with North American skunks, we don't really know all that much about it, and it's probably <a href="https://www.researchgate.net/profile/Belden-Giman/publication/298354311_Distribution_of_Sunda_Stink_Badger_In_Sarawak_Malaysia/links/56e8b79c08aec65cb45ecfbd/Distribution-of-Sunda-Stink-Badger-In-Sarawak-Malaysia.pdf" target="_blank">not quite as widespread</a> as it once was. Stink badgers are about the same size as striped skunks, only weighing around 2.5 kg (5 lbs 8 oz.), but otherwise have the stocky build and short, muscular limbs we would expect of a badger. They are very dark brown in colour, rather than black, with a white or off-white patch of fur on the head and, sometimes, a narrow white stripe down the back. The tail is white and has far shorter fur than that seen on other skunks; there is no "bottlebrush" threat display seen in other skunks. The narrow, slightly elongated, head is almost hairless on the snout.</p><p>And, yes, as their name suggests, stink badgers are more than capable of spraying potential threats with a noxious fluid from their anal glands. This does not appear to have been analysed in any detail that I can find (although some of the components are used locally in perfumes - presumably in very small quantities) but it's said to be potent enough to blind or even asphyxiate dogs. While this might sound like a clue to their skunky nature that we should have spotted earlier, it's worth noting that <a href="https://synapsida.blogspot.com/2012/09/weasels-on-savannah-zorillas-and-their.html" target="_blank">zorillas</a> can do the same thing - and they really are mustelids.</p><p>Despite their generally wild distribution stink badgers are not common in the dense primeval forests that cover much of their native islands, preferring more open woodland, whether that be because it is on the natural periphery of denser jungle or has been partially cleared by human activity. <a href="https://repository.naturalis.nl/pub/509142/" target="_blank">19th-century accounts</a> reported them at elevations of over 2000 metres (6,500 feet) but they also seem common in the <a href="https://www.researchgate.net/profile/Meaghan-Evans/publication/306259866_Small_carnivores_of_the_Lower_Kinabatangan_Wildlife_Sanctuary_Sabah_Borneo_including_a_new_locality_for_the_Otter_Civet_Cynogale_bennettii/links/57b547bc08ae19a365fafe5e/Small-carnivores-of-the-Lower-Kinabatangan-Wildlife-Sanctuary-Sabah-Borneo-including-a-new-locality-for-the-Otter-Civet-Cynogale-bennettii.pdf" target="_blank">lowlands</a>, perhaps down to sea level. They may inhabit caves in the mountains, but more commonly use burrows, whether those they have dug themselves or appropriated from other animals. These are not the deep complex burrows of European badgers, not least because stink badgers at best live in pairs, rather than communal setts, and are usually no more than 60 cm (2 feet) deep. </p><p>Stink badgers are <a href="https://orca.cardiff.ac.uk/id/eprint/101953/" target="_blank">nocturnal</a> and omnivorous. In the wild, they feed on insects, worms, eggs, and carrion, alongside whatever plants may be local to the area. Earthworms seem to be their preferred food, and they spend a fair amount of their time rooting around in the soil with their hairless snout and large fore-claws trying to find them. It has been suggested that the distribution of stink badgers is influenced by places where the soil is best suited for earthworms, although the evidence for this is <a href="https://doi.org/10.1016/j.mambio.2017.11.010" target="_blank">currently weak</a>.</p><p>Most of their other habits remain a mystery, at least to Western science. The females have six teats, which suggests a maximum litter size of that number, but two or three young is apparently more typical. Presumably, these are raised in burrows, but the details remain unknown.</p><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody><tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg5DOQ1vyfC_ZoE7ESQ6fA1uVJJrDDQ1cP4-_hbvK5qvdo8Xevkd5RbxXeNceWJ4tZnKoLb93uehrEo7iD09SOXll51o_Vbxj0LP6le5B-y1zPw7Ebh3n6M8MAaIRGN8c_IpCN2s93URnFU3bAPlkUlFU12a13wb68FInwTOMQhoIO7Nwt1mOpJWBybG3Qp/s400/800px-Mydaus_marchei_Palawan_stink_badger_Huet_1887.jpg" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="272" data-original-width="400" height="218" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg5DOQ1vyfC_ZoE7ESQ6fA1uVJJrDDQ1cP4-_hbvK5qvdo8Xevkd5RbxXeNceWJ4tZnKoLb93uehrEo7iD09SOXll51o_Vbxj0LP6le5B-y1zPw7Ebh3n6M8MAaIRGN8c_IpCN2s93URnFU3bAPlkUlFU12a13wb68FInwTOMQhoIO7Nwt1mOpJWBybG3Qp/s320/800px-Mydaus_marchei_Palawan_stink_badger_Huet_1887.jpg" width="320" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">Palawan stink badger</td></tr></tbody></table><p>The second species was not identified as such until 1887. The <b>Palawan stink badger</b> (<i>Mydaus marchei</i>) lives only in the southwestern Philippines, on Palawan and the Calamian Islands. For a while in the 20th century, it was considered distinct enough to be given its own genus, but it's hard to see why, since the two species are difficult to tell apart. The Palawan species is slightly smaller, with adults weighing about 2 kg (4 lbs 4 oz.), with a shorter tail, and ears that are so small as to be almost invisible... but otherwise, it's essentially the same as its more widespread relative.</p><p>We know even less about the Palawan species than we do the Sunda one and the little we do know suggests that they're behaviorally, as well as physically, similar. They inhabit lowlands (there are mountains on Palawan, but they only just reach 2,000 metres, so the badgers couldn't be found higher than that anyway) including grasslands and swamp as well as open woodland. While the Sunda species apparently avoids plantations, the Palawan one does not similarly avoid <a href="https://smallcarnivoreconservation.com/index.php/sccg/issue/view/299/101" target="_blank">rice paddies</a>, especially where they are close to scrubby bushes suitable for hiding in. They are said to eat molluscs and small crabs as well as the same types of food eaten by their relatives.</p><p>When approached by humans or other potential threats, they snarl and stamp their feet, much as a regular skunk would. One individual was <a href="https://www.cambridge.org/core/journals/oryx/article/palawan-stink-badger/D7FFDEE1F0FD9E414FC98191B46850B1" target="_blank">reported</a> to pretend to be dead when a researcher touched it... but when he tried to pick it up and carry it elsewhere, it eventually decided to spray him. Oddly, he later said that the smell was "pungent but not offensive", comparing it to almonds and certain kinds of ant. He also saw the badger using the same secretions to mark the trails it walked along, so it's likely that it isn't purely defensive as it is in regular skunks.</p><p>All of which represents essentially our entire knowledge of the species. It also brings me to the end of the living members of the skunk family. We do know of some <a href="https://www.researchgate.net/profile/Xiaoming-Wang-43/publication/267156609_Passing_the_smell_test_in_tracing_the_skunk_lineage_appearances_can_be_deceiving_so_can_odors/links/544739da0cf2f14fb811d731/Passing-the-smell-test-in-tracing-the-skunk-lineage-appearances-can-be-deceiving-so-can-odors.pdf" target="_blank">fossil skunks</a>, however, with the oldest North American example being <i>Martinogale</i>, which lived in California about 9 million years ago, and either was, or was <a href="https://doi.org/10.1671/0272-4634(2005)025[0936:ANBSMC]2.0.CO;2" target="_blank">closely related</a> to, the first skunk to reach the continent from Asia. It was about the size of modern spotted skunks - that is, quite a bit smaller than the striped sort - and, despite some primitive features, probably already looked very skunk-like. Obviously, we can't know how good it was at spraying from what's basically a well-preserved skull, but every living skunk is, so it's a fair bet.</p><p><i>Martinogale</i> is followed by <i>Buisnictis</i>, which is known from Mexico to Kansas, and lived from around 5 to 2 million years ago, during the Pliocene. Its teeth more closely <a href="https://doi.org/10.1080/14772019.2013.776647" target="_blank">resemble</a> those of modern American skunks, and it could even be their direct ancestor. (We can't know this, of course, but at present, we have no other candidates, so it's at least plausible). It's likely that the first skunks crossed into South America, to give rise to the hog-nosed species of today, around 2 million years ago when the Panama land bridge opened up, with the striped and spotted skunks of the north diverging from one another not much later, perhaps when they were separated by the advancing ice sheets.</p><p>The origin of the stink badgers is less clear, since we lack any fossils showing clear relationships to them. However, we can be confident that skunks first appeared in Asia and headed east, rather than going the other way, because some of the Asian fossils we do have are older than <i>Martinogale </i>and this also fits with what we can infer of their origins from mustelid-like animals. The best-known of these is <i>Promephitis</i>, which first appeared around 11 million years ago and survived right through to the start of the Ice Ages 2 million years ago. That's far too recently for it to be the ancestor of stink badgers, and its precise placement within the family is unclear. Similar in size to a modern striped skunk, it lived across Eurasia from <a href="https://doi.org/10.1007/978-3-030-68442-6_23" target="_blank">Greece</a> to China showing that skunks were once <a href="https://doi.org/10.1671/0272-4634(2004)024[0721:LMPCMF]2.0.CO;2" target="_blank">widespread</a> on this continent. Indeed, <i>Palaeomephitis</i>, which lived 12 million years ago in Europe, may be the <a href="https://bibliotekanauki.pl/articles/22582.pdf" target="_blank">oldest known skunk</a>, but its remains are sufficiently fragmentary that we <a href="https://doi.org/10.5252/g2016n4a5" target="_blank">can't currently be sure</a>.</p><p>In any event, genetic evidence suggests that skunks are much older than this, likely having first appeared some time during the Oligocene, around 30 million years ago. The gap between this date and the oldest known fossils is large enough that we can't be sure when the powerful stink glands would have first appeared - for all we know, they may be a feature of the one branch of the family that survives, arising relatively recently in the common ancestor of stink badgers and American skunks. </p><p>Skunks, raccoons, and mustelids together form an evolutionary group called the "musteloids", a collection of smallish carnivores that often, but not always, tend towards omnivory. However, not all living musteloids fit into one of these three families. There is one exception, and I will round out the year by taking a look at the odd one out...</p><p><i>[Photo by "<a href="https://commons.wikimedia.org/wiki/User:U.Name.Me" target="_blank">U.Name.Me</a>" from Wikimedia Commons, drawing by J. Huet, in the public domain. Cladogram adapted from <a href="https://doi.org/10.1080/03949370.2012.744359">Caro et al. 2012</a> and <a href="https://doi.org/10.1016/j.ympev.2021.107266">McDonough et al 2022</a>.]</i> </p><p></p>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com0tag:blogger.com,1999:blog-4209921721314660731.post-29024353993436399012023-10-29T16:02:00.002+00:002023-10-29T16:54:11.150+00:00Oligocene (Pt 5): The First Cats<p></p><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody><tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjRh57h0pI428B1TKrHwVAVHJjLZ8JNzT_lKfK0YD8xuA7FaXBkJikOLU3Prkt4hE9iwDcvGRsMS1aplcOYfSOQHZaMeFHw1ZsV8neBvNqmK3_2-x8GV5GxuFyy-s7STNBOfa0iCzUYZjHH6ikyhwafoXIUv1Lo6szGVf_L8TdeIo1mt5vGBVsDNg_ECNnW/s400/800px-Proailurus_lemanensis_skull.jpg" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="261" data-original-width="400" height="209" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjRh57h0pI428B1TKrHwVAVHJjLZ8JNzT_lKfK0YD8xuA7FaXBkJikOLU3Prkt4hE9iwDcvGRsMS1aplcOYfSOQHZaMeFHw1ZsV8neBvNqmK3_2-x8GV5GxuFyy-s7STNBOfa0iCzUYZjHH6ikyhwafoXIUv1Lo6szGVf_L8TdeIo1mt5vGBVsDNg_ECNnW/s320/800px-Proailurus_lemanensis_skull.jpg" width="320" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;"><i>Proailurus</i></td></tr></tbody></table>As new herbivores entered Europe at the <a href="https://synapsida.blogspot.com/2023/05/oligocene-pt-2-europes-big-break.html" target="_blank">Grande Coupure</a>, carnivores were bound to follow. As with their prey, these Asian newcomers seem to have rapidly outcompeted the native European forms, leading to a sudden turnover in the types of animals we find on the continent. Although we can say that these newcomers were "carnivorans" - the sort of mammalian carnivores we're mostly familiar with today - where exactly they place relative to the living families is harder to say.<p></p><p><i>Plesictis</i> is an example here. It looked, so far as we can tell, rather like a polecat and was about the same size, so for much of the 20th century it was thought to be an <a href="https://www.researchgate.net/profile/Jon-Baskin/publication/313172909_Mustelidae/links/5dd050ff4585156b35197762/Mustelidae.pdf" target="_blank">early example</a> of a mustelid, albeit one no more closely related to actual polecats than, say, badgers or otters are. More modern analyses are more circumspect; it may look like a <b>mustelid</b> in some respects, but it probably lived <a href="https://doi.org/10.1016/j.ympev.2012.02.025" target="_blank">before</a> those animals diverged from the raccoons and so can't be quite either. <i>Palaeogale</i>, which looked rather similar and was also originally assumed to be a mustelid, in fact turns out to be more related to cats and mongooses, but probably <a href="https://www.researchgate.net/profile/Vertebrata-Palasiatica/publication/286134862_Phylogenetic_analysis_on_Palaeogale_Palaeogalidae_Carnivora_based_on_specimens_from_Oligocene_strata_of_Saint-Jacques_Nei_Mongol/links/56665d6a08ae192bbf92806d/Phylogenetic-analysis-on-Palaeogale-Palaeogalidae-Carnivora-based-on-specimens-from-Oligocene-strata-of-Saint-Jacques-Nei-Mongol.pdf" target="_blank">so far down</a> the family tree that it's not yet possible to say much more than that.<span></span></p><a name='more'></a><p></p><p>The same rich fossil deposits of Quercy in southern France that revealed the first fossils of <i>Plesictis</i> also gave us those of <i><b>Amphicynodon</b></i>. This was a similar size, but certain features of the skull made it apparent that it was related in some way to bears. For a long time, all we had was the skull but in the last few years we have been able to examine more complete skeletons. These reveal an animal weighing about 2 kg (4 lbs), similar to a large ferret, with grasping forepaws and mobile hips that suggest it would have been adept at climbing. It probably spent much of its time <a href="https://hal.science/hal-03915284/" target="_blank">in trees</a>, and the hind ankles were able to swivel so that it could, potentially, have <a href="https://doi.org/10.1007/s10914-022-09621-9" target="_blank">hung upside down</a> from its hind feet to grasp at prey and it would likely have bounded from branch to branch with alacrity.</p><p>Modern interpretations describe it as an "arctoid"; a general category of early carnivores that include the ancestors of bears, seals, and the weasel/raccoon/skunk clade. Although it isn't entirely certain, it's unlikely to be a direct ancestor of any of those groups itself, and is typically given its own family. Although earlier arctoids did exist in Europe, it likely came across in the Coupure, rather than evolving locally, and it <a href="https://doi.org/10.1206/0003-0090(2003)279%3C0116:C%3E2.0.CO;2" target="_blank">may be related</a> to the Mongolian <i><a href="http://dx.doi.org/10.1206/0003-0082(2005)483[0001:AAAACF]2.0.CO;2" target="_blank">Amphicticeps</a></i>, a more purely carnivorous (rather than omnivorous, as <i>Amphicynodon</i> likely was) animal of similar size.</p><p>Giving them their own family does create some potential confusion, however, since, under the rules of such things, the family name ends up as "amphicynodontids" which sounds remarkably similar to "amphicyonids", a separate group more commonly known as <b>bear-dogs</b>. These are better known from the subsequent, Miocene, epoch, where they attained bear-sized proportions despite keeping their narrower heads and long tails. Oligocene examples from Europe include <i>Pseudocyonopsis</i> and <i>Goupilictis</i>, smaller, more dog-like animals with an omnivorous diet that already leaned more towards small mammals than plants.</p><p>By most modern definitions, the earliest known true <b>bear</b> was <i>Cephalogale</i>, with fossils from the Czech Republic, and which is known to have survived a short way into the Miocene epoch in Spain. This looked much more like a dog than it did a bear; the size of the different species was highly variable, but most seem to have been <a href="https://doi.org/10.1007/s13358-011-0034-3" target="_blank">comparable</a> to a mid-sized domestic dog of today. It was probably already omnivorous, and its teeth seem as well-adapted to crushing plants as to slicing meat.</p><p><i>Eusmilus</i> was rather more deadly. This was the first <b>nimravid</b> to enter Europe, arriving shortly after the Coupure. The nimravids were related to cats, and looked remarkably similar, with their teeth in particular suggesting a purely carnivorous, cat-like diet. <i>Eusmilus</i> was about the size of a lynx, but with a sleeker build. More significantly, it had long sabre-like teeth, much like those of the true sabretooth cats that would appear much later, and a jaw adapted for the wide gape that employing these would have required. </p><p>More nimravids followed, including <i>Eofelis</i> and <i>Dinailurictis</i>, some of which had canines that, while still large, lacked the great length and flattened sabre-shape of those in <i>Eusmilus</i>. This suggests that nimravids, like the true cats in later times, were evolving down <a href="https://doi.org/10.1038%2Fs41598-021-00521-1" target="_blank">two different paths</a>, one sabretoothed and one (from our modern perspective) more "normal". The <a href="https://doi.org/10.1016/S1251-8050(00)00199-3" target="_blank">largest species</a> of <i>Eofelis</i> reached the size of a leopard, but it was not quite the largest carnivore on the continent at the time. That honour goes to <i>Quercylurus</i>, which estimates place between the size of a lion and a small bear. It's unlikely to have been fast-running, presumably sneaking up on its prey to suddenly pounce out at them. Its feet had flat soles, closer to those of a bear than a modern cat, perhaps in order to support its relatively high weight.</p><p>The nimravids may have been the largest <b>cat</b>-like carnivores on the continent, but they were not the only ones. <i>Stenoplesictis</i> is another creature that appeared after the Coupure, although the lack of obvious ancestors elsewhere makes it <a href="https://doi.org/10.1080/02724634.1999.10011165" target="_blank">harder to say</a> whether it came across from Asia or evolved locally. It would have been more <a href="https://d1wqtxts1xzle7.cloudfront.net/84178591/Sobre_un_craneo_de_civeta_del_Oligoceno_-libre.pdf?1649999738=&response-content-disposition=inline%3B+filename%3DSobre_un_craneo_de_civeta_del_Oligoceno.pdf&Expires=1698586435&Signature=P70IACjb0uGp-fY5WLVM5NW7U~NTN3aI9hLcspQ8Xh5kvR715nb~aCTNCKqOH2DHj-oXXFTEgzd-v~lix-hOcByNQlazxXO7cXO0iiYuaGUicC9DDczJlkezLuZ-MYupfr6vOAGNIj3ah8ayQHAbq7dtpwEcYgFdLr1O8RxhmW20jdnpXDT9BnD~JQrClLEZP4G63QTuxaGf7bfoEjoI1ofZXBlBgDbq3jwcfJfrVsnruz2hWfBkN2SY5VC-TcBJAff1BDdxZz1I85SKb9FAZA1wtg4JN3lB8q7C1vvfdhDpU0OaHTSAqtBQZHyNAEX4ysrncB3yT6K-hCFgDUV5TA__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA" target="_blank">like a civet</a> than anything else alive today and about all we can say is that it was <a href="https://doi.org/10.1080/08912963.2022.2045980" target="_blank">more closely related</a> to the living species of cat-like carnivores (cats, civets, mongooses, etc.) than it was to the nimravids.</p><p>In the latter half of the Oligocene, after the sudden cold snap of the Oi-2 glaciation, the large nimravids began to die out in Europe, although they survived elsewhere. Smaller carnivores like <i>Stenoplesictis</i>, however, did rather better, and began to diversify. Animals such as <i>Haplogale</i> and <i>Stenogale</i> began to develop a more explicitly cat-like form, with a shortened face and reduced cheek teeth suited for a highly carnivorous diet, but, while they are probably more closely related to cats than to, say, mongooses, they don't fit within any of the living families. </p><p><i>Proailurus</i>, however, is a different matter. First appearing in Europe around 25 million years ago, towards the end of the Oligocene, it is the <a href="https://doi.org/10.1206/0003-0082(2003)403%3C0001:PSONAP%3E2.0.CO;2" target="_blank">oldest known</a> member of the cat family. Its proportions were not quite those of the modern animals, being closer to those of living civets, but the head was already shortening, if not yet fully feline, and its teeth had evolved the highly specialised meat-slicing form seen in living cats. It was about <a href="https://doi.org/10.1111/jeb.12671" target="_blank">the size of an ocelot</a>, and thus larger than the domestic animal, and was adapted for climbing, and so probably spent a lot of time in the trees.</p><p>Not all of the carnivorous animals native to Asia crossed over to Europe at, or after, the Coupure although, for the most part, those that did not were reasonably close relatives of others that did. An exception worth mentioning are an obscure group called the didymoconids. Never leaving Central Asia, they had survived from the previous epoch, but continued on through the Oligocene, only dying out towards its end, with the best-known example, <i>Didymoconus</i>, living in Mongolia at this time. </p><p>This was a slender animal, about the size of a cat, with sharp teeth and large canines that suggest a carnivorous diet. Some features of the forelimbs, including their strength and shape as well as unusually solid-looking claws, suggest that it may been a <a href="http://dx.doi.org/10.1671/0272-4634(2001)021[0555:DMDFLB]2.0.CO;2" target="_blank">burrowing</a> animal, perhaps with a diet similar to that of modern badgers. Quite what sort of animal it was is far from clear, although it is no longer thought to be a true carnivoran as was originally the case. More recent suggestions include that it might be a relative of the <a href="https://www.researchgate.net/profile/Alexey-Lopatin/publication/236617498_New_Oligocene_Didymoconidae_Mesonychia_Mammalia_from_Mongolia_and_Kazakhstan/links/53e0debe0cf24f90ff60bdf3/New-Oligocene-Didymoconidae-Mesonychia-Mammalia-from-Mongolia-and-Kazakhstan.pdf" target="_blank">mesonychids</a>, strange carnivores related to the cloven-hoofed mammals that died out at the end of the Eocene, or that it was somehow related to shrews and moles. The chances are, however, that it <a href="https://www.researchgate.net/profile/Alexey-Lopatin/publication/236617857_The_Skull_Structure_of_Archaeoryctes_euryalis_sp_nov_Didymoconidae_Mammalia_from_the_Paleocene_of_Mongolia_with_comments_on_the_the_Taxonomic_Position_of_the_Family/links/53e0e4270cf24f90ff60bfdc/The-Skull-Structure-of-Archaeoryctes-euryalis-sp-nov-Didymoconidae-Mammalia-from-the-Paleocene-of-Mongolia-with-comments-on-the-the-Taxonomic-Position-of-the-Family.pdf" target="_blank">might not</a> have been closely related to anything alive today.</p><p>One thing we don't find anywhere in the Old World at the time are dogs. This is because they didn't enter Asia until almost the end of the following, Miocene, epoch, many millions of years later. So what was going on on their home continent during their early evolution. Next time, I will cross the Atlantic to find out by taking a look at some of the mammals of Oligocene North America...</p><p><i>[Photo by "<a href="https://commons.wikimedia.org/wiki/User:Ghedoghedo" target="_blank">Ghedoghedo</a>", from Wikimedia Commons.]</i></p>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com0tag:blogger.com,1999:blog-4209921721314660731.post-86648530857729198092023-10-22T17:29:00.003+01:002023-10-22T17:29:51.109+01:00Follow the Leader?<p><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiUt6NQwFBrk28p7eeWepkcRCYv1smcxzSBIX6h-VFox5BFxd94cMqURQziknPuvm99Nckj6fMU7i6Ff7zfA_uCZOg6qN9-KkiGQ7tmqE7rvN0rxiEVsSFkOsk3sRYb0xLWFLnDUzadR-_-44TdwdtINI2FiRTs8K2dU2DU_5pH3joPsycwJlRsIn-H5kqL/s400/Running_zebra.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em; text-align: center;"><img border="0" data-original-height="274" data-original-width="400" height="219" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiUt6NQwFBrk28p7eeWepkcRCYv1smcxzSBIX6h-VFox5BFxd94cMqURQziknPuvm99Nckj6fMU7i6Ff7zfA_uCZOg6qN9-KkiGQ7tmqE7rvN0rxiEVsSFkOsk3sRYb0xLWFLnDUzadR-_-44TdwdtINI2FiRTs8K2dU2DU_5pH3joPsycwJlRsIn-H5kqL/s320/Running_zebra.jpg" width="320" /></a>By human standards, the majority of mammal species are comparatively antisocial. Some actively avoid others of their kind outside of the mating season, but even those that are more tolerant are often found together in one place purely because that is where the <a href="https://doi.org/10.3354/meps215275" target="_blank">food happens to be</a>. But, of course, there are a great many exceptions to this; animals that habitually live in groups that socialise and travel together.</p><p>Animals that live like this have to have some form of decision-making process that all members of the herd, pack, or other grouping choose to abide by. The most obvious example of this would be deciding when and where to move, but it could also include, for example, determining the best way to escape predators. Lacking the sophisticated communication methods of humans, concepts of debate aren't likely to be applicable, but the decision has to be taken somehow, and, over the years, there have been many studies to determine just how egalitarian the process is and exactly which animals within the group are making the decisions if it isn't.<span></span></p><a name='more'></a><p></p><p>According to a <a href="https://doi.org/10.1111/mam.12321" target="_blank">recent review</a> of such studies, there has been far more focus on some types of mammal than others. In part, this is due to the uneven distribution of group living across the mammalian family tree - questions about leadership and group decision-making aren't going to be relevant to animals that live their lives alone. But there are other biases as well, due to what sorts of things researchers are likely to be interested in, and how easy the animal might be to study. </p><p>The review showed that nearly half of all studies on animal leadership are conducted on primates - mostly monkeys, but also lemurs and apes. One can easily see why those would be a favoured topic of research, given the likely richness of primate interactions and their obvious relevance to our own species. Just over a third of studies are conducted on cloven-footed herd animals, including those on farms (sheep, goats, cattle) as well as their wild relatives such as bison and deer - although there have been relatively few on antelopes, probably because there are so few in Europe and North America. </p><p>The remaining fraction are more or less evenly split between horses, pack-hunting carnivores, and aquatic mammals. The last of these, of course, are going to fall into the "difficult to study" category, as would bats, which seem to have been almost totally ignored - presumably for this very reason.</p><p>When we're looking at a broad sweep of different species like this, there will inevitably be subtle differences in how each of them behaves so it can be useful to try and fit these into <a href="https://doi.org/10.1016/j.tree.2005.05.008" target="_blank">general categories</a>. When we do this, we find that the most common pattern is for each group to have a single, identifiable leader that takes all the decisions and expects everyone else to follow them. </p><p>We see this in herd animals, such as <a href="https://doi.org/10.1111/j.1439-0310.1984.tb00355.x" target="_blank">zebras</a>, the herd stallion not only leads the group towards sources of water, but also tries to keep the herd together and goes so far as to threaten unruly subordinates who might sow discord within the group. In that case, the leadership position is long-lasting, but it doesn't have to be; it could switch between different individuals as the situation demands. In muskoxen, for example, <a href="https://doi.org/10.1644/10-MAMM-A-109.1" target="_blank">dominant females</a> are in charge of deciding when and where the herd moves in search of forage - but it doesn't have to be the same individual every time. There are, in effect, a small number of potential leaders who take turns. Among primates, <a href="https://www.jstor.org/stable/40295873" target="_blank">female gibbons</a> also take turns leading their groups, with pregnant or nursing individuals being prepared to take a back seat to focus on what's presumably more important to them.<span></span></p><p>Among wolves, we have the myth of the "alpha male", a term that used to be <a href="https://doi.org/10.1093/icb/7.2.305" target="_blank">common</a> in the scientific literature but that turns out to be rather misleading. In reality, the dominant female is <a href="https://doi.org/10.1139/z02-124" target="_blank">just as likely</a> to lead the pack to new hunting grounds as the dominant male and a better term for the resulting "alpha pair" turns out to be "parents". </p><p>One would expect that the individual to physically leads the group, by heading to a new location, would also be dominant in other ways. This is certainly the case with wolves and it's also seen in many <a href="https://doi.org/10.1007/s10164-009-0162-z" target="_blank">primate</a> societies, as well as in cloven-footed herd animals such as <a href="https://doi.org/10.1016/j.applanim.2007.01.009" target="_blank">cattle</a> and <a href="https://doi.org/10.3758/BF03334540" target="_blank">sheep</a>. However, this doesn't have to be so, and not all group-living mammals necessarily have a defined dominance hierarchy anyway. In which case, how do they decide who among them gets to choose where they should go next?</p><p>In some primate species, such as <a href="https://doi.org/10.1098/rsos.180991" target="_blank">red-fronted lemurs</a>, it has been proposed that the decision to move to new foraging grounds is made by the individual with the greatest investment in the answer - females that are pregnant or nursing young. Among Tibetan macaques, <a href="https://doi.org/10.1371/journal.pone.0127459" target="_blank">social connectivity</a> appears to be the answer; individuals may not be more "dominant", but if they are more generally popular and have numerous close associates, enough other animals will follow when they move that the entire band is obliged to do so as well. It's almost rule by celebrity, rather than by coercion and physical dominance.</p><p>Another possibility, which might seem rather radical by human standards, is to follow those who know what they're doing. This has been <a href="https://www.jstor.org/stable/4536187" target="_blank">proposed</a> for sifakas (close relatives of lemurs) where it may be that females lead because they will have grown up in an area, and know where the best food or shelter is likely to be, while the males leave home when they reach adulthood and are less tied down to a particular place. A similar situation is seen in vervet monkeys, where there seems to be a <a href="https://doi.org/10.1002/ajpa.23058" target="_blank">distributed leadership</a> where a group of experienced females (rather than a single individual) collectively decides where to go based on their knowledge of the environment.</p><p>This sort of oligarchic setup seems to be comparatively rare, but there are some mammal species that apparently do without leaders at all. Meerkats use what has been described as a <a href="https://doi.org/10.1098/rspb.2010.1739" target="_blank">"quorum" system</a>, whereby if enough individuals signal their intention to do something by calling to one another, the entire group decides it's a good plan. Of course, they are unlikely to be literally counting the number of votes, it's more a rough idea of "that's enough to be worth listening to", but the idea is the same - the greater the number of individuals wanting something to happen, the more likely it is that it will. In a similar vein, one of the few studies of leadership among bats suggests that at least one species decides <a href="https://doi.org/10.1016/j.beproc.2015.09.005" target="_blank">where to roost</a> simply based on whatever is most popular with the bats that got there first.</p><p>African wild dogs also take group decisions on whether to leave an area, <a href="https://doi.org/10.1098/rspb.2017.0347" target="_blank">sneezing</a> to vote "yes". Although it's clear that the "vote" of a dominant individual is worth more than that of a subordinate one, they don't always get their own way if enough others disagree.</p><p>This is also what we would probably expect of group-living aquatic mammals, be they dolphins, whales, or seals. Out in the open waters, the lack of any boundaries and the three-dimensional nature of the habitat make controlling a territory difficult at best, and it's hard to monopolise control over resources that are equally mobile. As a result, aquatic mammals are not territorial and they usually have little, if anything, in the way of <a href="https://doi.org/10.1098/rstb.2018.0066" target="_blank">dominance hierarchies</a>. </p><p>Decisions such as when to dive into an extreme habitat where food may be patchily distributed are clearly going to be important to such animals. We know that they do, like land-dwelling herd and pack animals, <a href="https://doi.org/10.1038/s41598-019-55911-3" target="_blank">coordinate</a> their movements where they live in pods or other accumulations, but having a single decision-maker for such issues seems unlikely for animals that are generally egalitarian. </p><p>In the case of seals, which certainly do have dominance hierarchies when it comes to mating, there do not appear to be any studies about leadership decisions out in the ocean. But, despite the difficulty of the studies, we do have evidence of this behaviour among dolphins - and it turns out that central leadership is much more common among such animals than we might think. In <a href="https://doi.org/10.1007/s00265-009-0740-7" target="_blank">bottlenose dolphins</a>, for instance, decisions about when to travel are apparently made by a single male individual. Which individual that is seems to be determined by their <a href="https://doi.org/10.1007/s10682-006-9105-0" target="_blank">experience</a> rather than being "dominant" in other respects over his fellows. </p><p>Knowledge and experience, it seems, trump physical prowess or general bossiness among dolphins.</p><p>Similarly, in killer whales, it's the older, menopausal, females that <a href="https://doi.org/10.1016/j.cub.2015.01.037" target="_blank">lead the pod</a>. Their ability to lend the benefit of their accumulated wisdom to their fellows is probably the main reason why killer whales even have a menopause; in almost every other mammal species, individuals don't survive past reproductive age, since they can no longer pass their genes on to their descendants, making them evolutionarily redundant. </p><p>Normally, by consuming food that their children could have instead, a menopausal mother would actually harm her offsprings' chance of survival, but if they can help them survive by leading them to better food sources and knowing what to avoid, their accumulated wisdom can be a plus. Indeed, we see something similar among <a href="https://doi.org/10.1163/1568539X-00003465" target="_blank">elephants</a>, one of the few other mammals to experience menopause, although here, there's a clearer dominance hierarchy.</p><p>Having said which, it might not always be so simple. There is evidence that bottlenose dolphins, for instance, do have <a href="https://doi.org/10.1016/j.anbehav.2020.03.001" target="_blank">personalities</a>, with some being shy and others more outgoing, so it's entirely plausible that the latter may be more inclined to "take charge" even if they aren't quite so experienced. Sperm whales also manage to coordinate their movements despite the fact that their groups consist of individuals that are literally miles apart from one another. Presumably, they do this by signalling audibly to one another, but so far as we can tell, they aren't following a single leader when they do so.</p><p>Sperm whales, at least, seem to have something approaching democracy, even if the slow and slightly confused manner in which their groups change direction at sea implies that it's about as messy for them as politics can sometimes be for us. </p><p><i>[Photo by "<a href="https://commons.wikimedia.org/wiki/File:Running_zebra.jpg" target="_blank">Touhid biplob</a>", from Wikimedia Commons.]</i></p>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com0tag:blogger.com,1999:blog-4209921721314660731.post-79840538638386401142023-10-15T16:05:00.001+01:002023-10-15T19:19:00.859+01:00Attack of the Giant Hyenas<p></p><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody><tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhp7iPtQuosqD9_29D3I2T0hUZ71ci9-5v0gOxjakKnx4EhPzDRQUrK7A3hEL8V1KexAROgzQBlL38U_oXcWS3vv6WZrEmDsfFFPRXE61wPmxiB_ROSB-noEN3gjO962uDASQwI0pvbvn8meFsPZixwgVHdY_Vp_zruw0qaBYb0p0NHVw3K72ZCmPXxl_Qz/s400/800px-Crocuta_macrodonta.jpg" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="326" data-original-width="400" height="261" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhp7iPtQuosqD9_29D3I2T0hUZ71ci9-5v0gOxjakKnx4EhPzDRQUrK7A3hEL8V1KexAROgzQBlL38U_oXcWS3vv6WZrEmDsfFFPRXE61wPmxiB_ROSB-noEN3gjO962uDASQwI0pvbvn8meFsPZixwgVHdY_Vp_zruw0qaBYb0p0NHVw3K72ZCmPXxl_Qz/s320/800px-Crocuta_macrodonta.jpg" width="320" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;"><i>Dinocrocuta</i></td></tr></tbody></table>I suspect that most non-specialists would assume that hyenas are fairly closely related to dogs. They certainly look more like dogs than they do anything else, so, absent any further information, that seems reasonable enough. But, in reality, hyenas belong to the cat-like, not the dog-like, branch of the carnivoran family tree.<p></p><p>This isn't some new discovery on the basis of molecular evidence, like the splitting off of the skunks from the weasel family; it's been known for a long time. This is because, when you start looking at the structural details of the skull, especially the area around the ear, everything fits with a cat-like ancestry. This much was already obvious when <a href="https://en.wikipedia.org/wiki/Mikl%C3%B3s_Kretzoi" target="_blank">Miklós Kretzoi</a> formally named the two carnivoran branches while he was working at the National Museum of Hungary during World War II. Modern evidence has merely confirmed the view, showing more precisely that the closest living relatives of the hyenas are the mongooses.<span></span></p><a name='more'></a><p></p><p>In fact, the earliest known fossil "hyenas" do, in fact, look a lot like mongooses in both size and shape, and probably had a similar diet. The shift towards the modern hyena lifestyle is one that took millions of years, with the animals becoming much bulkier in the process. While they have been regarded as a distinct family of mammals for over two centuries now, when it comes to fossils, however, there is naturally some question as to what exactly belongs in the family and where to draw the boundaries. Opinions on this have changed over the years.</p><p>For example, take the case of the genus <i><b>Percrocuta</b></i>. Fossils of this hyena-like animal were first discovered in Europe in 1913, although we now know that various species assigned to the genus lived across Asia and into at least central Africa. Originally placed with the striped hyenas, even when Kretzoi recognised the genus of those original fossils as being <a href="http://publication.nhmus.hu/pdf/annHNHM/Annals_HNHM_1937-38_Vol_31_m_88.pdf" target="_blank">distinct</a> in 1938, he considered them to at least belong to the hyena family. </p><p>Over the following decades, they were slowly shifted further and further away, partly because better and more complete fossils were discovered, including some that could be assigned to different species within the genus. The break finally came in 1991, when researchers <a href="https://doi.org/10.18261/8200374815-1991-01" target="_blank">split off</a> <i>Percrocuta</i> and its close relatives and placed them in their own family: the Percrocutidae, or "false hyenas". This was on the basis of the shape of some of their teeth which, it was argued, showed that percrocutids were more closely related to cats than to mongooses and true hyenas.</p><p>Then the pendulum swung back again. First, most of the other genera in the newly named group were shifted back to the true hyenas again, then it was decided that, no, actually, the remaining "false hyenas" really were closely related to the regular sort. Today, the general opinion seems to be they are a subfamily <a href="https://doi.org/10.1080/08912963.2022.2067757" target="_blank">within the true hyenas</a>, although the issue is not fully settled, and there are still some who would consider them merely the closest known relatives of the living animals and thus allowed to keep <a href="https://doi.org/10.1080/08912963.2023.2263866" target="_blank">their own family</a>.</p><p>Regardless of what they really are, and what they are most related to, we can at least say that, as currently defined, the "false hyenas" (or whatever we want to call them) are a genuine group of animals, and they're certainly as worthy of study as anything else. It's not an exceptionally big group, consisting of just two genera, although with over a dozen species between them. <i>Percrocuta</i>, which lived in the Middle Miocene, is, of course, one of those genera, while the other its descendant - the <b>giant hyena</b>, <i>Dinocrocuta, </i>which died out, without descendants of its own, some time around 5 million years ago.</p><p>It's not called the "giant hyena" without good reason. One estimate is that the largest, <i>D. gigantea</i>, weighed somewhere around <a href="https://doi.org/10.1111/j.1095-8312.2008.01095.x" target="_blank">200 kg</a> (440 lbs), roughly comparable to an adult male brown bear. Since, in other respects, it looked quite like a modern hyena, we can safely assume that it wasn't something you'd want to get too close to if it was alive today.</p><p>But that was the largest one. Just how fearsome were the others, including the smaller and more primitive <i>Percrocuta</i> species? Even if they really were members of the hyena family, that doesn't mean that they lived like the typical modern species do. That's because, when we look at the full range of fossil hyenas, it seems that they had a pretty wide range of lifestyles. Some of the most primitive were probably omnivores and insectivores, much like the mongooses to which they were related. While even <i>Percrocuta</i> isn't small enough for that to be likely, there are other possibilities. Some prehistoric hyenas were relatively predatory, chasing down their prey like a wolf or cheetah (although obviously not quite as fast as the latter) while others were, like the modern species, specialised for cracking open bone, often from scavenged carcasses rather than anything they had killed themselves.</p><p>And, of course, we're ignoring the one living species of the hyena family that eats almost nothing but termites. We'd probably have noticed if <i>Percrocuta</i> was that strange.</p><p>Among the regular hyenas, this variation has been catalogued and refined by a series of <a href="https://doi.org/10.7717/peerj.6238" target="_blank">studies</a> since the 1990s. However, because of the complicated taxonomic history of the group, when the studies were conducted, <i>Percrocuta</i> and <i>Dinocrocuta</i> were considered to belong to a different family, and so were not included. That has now changed, with a 2023 study <a href="https://doi.org/10.1080/02724634.2023.2197972" target="_blank">comparing</a> these two genera with various others that are undeniably "true" hyenas.</p><p>The analysis, like the ones before it, looked specifically at the teeth at the back of the mouth. These are often more distinctive than those at the front, and more specifically adapted to the type of diet - in this case, we want to know whether they are better adapted for slicing through tough meat like a knife or for crushing bones like a hammer. </p><p>The analysis showed that species of the genus <i>Percrocuta</i> followed a similar evolutionary pattern to those of the ancestors of living hyenas, becoming better at cracking bone as they evolved through time. But there was a crucial difference: they did it earlier. For example, the first hyena capable of limited bone-cracking was, under the older classification system, <i>Metahyaena</i>, which lived in Turkey around 11 million years ago. Species such as <i>P. abessalomi</i> were doing the same thing 15 million years ago, and by 12 million years ago had already evolved to the specialised form we see in modern spotted hyenas, which their own ancestors didn't reach until around 8 million years ago.</p><p>Whether <i>Percrocuta</i> counts as a "true" hyena or not, it was living in the same way 4 million years before the modern kind got started, only later being supplanted by what we have now.</p><p>The giant hyenas were a different matter. Appearing later, and probably having evolved from some form of <i>Percrocuta</i>, the early ones were already bone-eating scavengers. These include <i>D. algeriensis</i>, which lived in Algeria at the same time as the (presumed) <a href="https://doi.org/10.1080/02724634.2021.2047990" target="_blank">first pure scavenger</a> in the rest of the family, <i>Allohyaena</i>, lived in Ukraine. From there, however, as the animals grew in size, the shape of the teeth at the back of the upper jaw began to shift, not only becoming larger, but sharper. By the time we reach <i>D. gigantea</i> - the bear-sized one - these teeth look to be even better at slicing through fresh meat than those of the most specialised of the earlier hunting hyenas, such as the "running hyena" <i>Chasmaporthetes</i>.</p><p>This makes it hard to escape the idea that these, the largest hyenas ever to have lived, were not mere scavengers, but active predators. This fits with the discovery of a fossil rhinoceros in China that showed what looked like the <a href="https://doi.org/10.1007/s11434-010-3031-9" target="_blank">bite marks of a giant hyena</a> on its skull. Modern spotted hyenas are certainly predatory, rather than living purely on carrion, but this new evidence suggests that giant hyenas may have been even more so, making them even more dangerous than their size alone would suggest.</p><p>At the same time, they retained some of the heavy <a href="https://doi.org/10.1111/j.1095-8312.2008.01095.x" target="_blank">bone-cracking</a> teeth in the lower jaw, so there probably wouldn't have been much left of any carcass by the time they had finished with it.</p><p><i>[Photo by "<a href="https://commons.wikimedia.org/wiki/File:Crocuta_macrodonta.JPG" target="_blank">Laikayiu</a>", from Wikimedia Commons.]</i></p>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com0tag:blogger.com,1999:blog-4209921721314660731.post-10050784907980264922023-10-08T17:29:00.001+01:002023-10-08T17:29:43.522+01:00Skunks of the World: Hog-nosed Skunks<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody><tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhPMbhmjIw-Zyph7cggfXE0PSYYH-76C6oJ6QlzkqqBcO_M0JUZnqfyuxjK735aEPvGX7yxrJzdHupsRrBQb_a6kYuNx95ADM9FRcEN1z2HiZ-TFFm49S1PM3KxpUniiVS7vEcxAZA-wDaEqxtKbaNyolxiSjuqSz4OlAzX0L0nH8P7ul2uKTwbt0SX8F1M/s400/Conepatus_leuconotus_leuconotus_843835.jpg" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="323" data-original-width="400" height="258" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhPMbhmjIw-Zyph7cggfXE0PSYYH-76C6oJ6QlzkqqBcO_M0JUZnqfyuxjK735aEPvGX7yxrJzdHupsRrBQb_a6kYuNx95ADM9FRcEN1z2HiZ-TFFm49S1PM3KxpUniiVS7vEcxAZA-wDaEqxtKbaNyolxiSjuqSz4OlAzX0L0nH8P7ul2uKTwbt0SX8F1M/s320/Conepatus_leuconotus_leuconotus_843835.jpg" width="320" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">American hog-nosed skunk</td></tr></tbody></table>There are, perhaps surprisingly, at least five different species of skunk living in the US. In fairness, two of them - the <a href="https://synapsida.blogspot.com/2023/09/skunks-of-world-spotted-skunks.html" target="_blank">spotted skunks</a> - are so similar to one another that it took genetic tests in the 1990s to prove they were more than subspecies, while the striped and hooded skunks are at least superficially similar as well. The fifth one is the <b>American hog-nosed skunk</b> (<i>Conepatus leuconotus</i>) and it's neither striped nor spotted.<div><br /><div>If it's less familiar than the others, even to many Americans, that may be because it's only found in the southwest. It is common across Mexico, and also lives across Central America as far south as northern Nicaragua, but in the US it's restricted to Arizona, New Mexico, and Texas. Even here, it doesn't inhabit the whole region, being found in only certain parts of those states and avoiding, for example, both the harsher deserts and dense woodland. Although it does live in some tropical habitats at the far southern end of its range, its <a href="https://doi.org/10.1017/S0266467402002328" target="_blank">preference</a> is instead for grassland and mesquite scrub, often with plenty of acacia thorn bushes. <span><a name='more'></a></span></div><div><br /></div><div>The precise range it inhabits may also have changed in recent years. Many online sources, for instance, show the animal as still living in southern Colorado and the western end of the Oklahoma panhandle, but, in reality, none have apparently been seen that far north since 1933. Populations in Texas have also declined, with them vanishing altogether from the eastern parts of the state. On the other hand, a new population may have become established in the <a href="https://smallcarnivoreconservation.com/index.php/sccg/article/view/3457" target="_blank">Grand Canyon</a>, where the skunks were previously absent, and they're probably common enough in Mexico.</div><div><br /></div><div>Physically, the hog-nosed skunk is similar in size to the striped skunk, but with a stockier build and a shorter tail. It is also known as the "white-backed skunk" because of its white back, unbroken by any black stripes or similar patterns - the animal is simply white above and black below. Besides the rather obvious lack of stripes, another distinguishing feature is the lack of a white spot or stripe on the upper snout. There is some indication that the white back may be <a href="https://doi.org/10.1002/9781118943274.ch6" target="_blank">more striking</a> in populations living in more open habitats, perhaps because the implied warning is more useful where it is clearly visible from a distance.</div><div><br /></div><div>The hog-nosed species is so-named because of the comparatively large and broad tip to its nose, although this is clearly well short of what you'd expect on an actual hog. Nonetheless, it uses this in a similar manner to pigs, rooting around in the ground and under rocks. In its case, it's looking for insects and grubs, something that the claws on its muscular forelegs also help with. Like most skunks, they will eat pretty much anything, including plant matter and meat from larger animals, but insects form a larger part of their diet than they do for striped or spotted skunks, and they are willing to spend hours looking for them if they get the chance.</div><div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgJforTI12ngqgRW1gp3AkYIFlzFVpH-5xQVx9ixtoCFT2E2tBRsGEEXTGv_C6zsaTOgAwOR35hoHEFThwgwvOYAkyU4gGS0jq2K-7pX8odIJKcxRYvHlSOrtsVQ-pceHPbAOydDwHKA2sCNZgBqzkE6kdPA-aM9V75ErTVPCyYGrGKFoytRILKiDLzbnxY/s400/Mephitidae-2.JPG" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" data-original-height="175" data-original-width="400" height="140" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgJforTI12ngqgRW1gp3AkYIFlzFVpH-5xQVx9ixtoCFT2E2tBRsGEEXTGv_C6zsaTOgAwOR35hoHEFThwgwvOYAkyU4gGS0jq2K-7pX8odIJKcxRYvHlSOrtsVQ-pceHPbAOydDwHKA2sCNZgBqzkE6kdPA-aM9V75ErTVPCyYGrGKFoytRILKiDLzbnxY/s320/Mephitidae-2.JPG" width="320" /></a></div><br />They are <a href="http://hdl.handle.net/2346.1/30019" target="_blank">primarily nocturnal</a>, although daytime activity is not especially rare. Like other skunks, they are solitary, but they don't seem to be territorial, <a href="https://doi.org/10.1674/0003-0031-174.2.310" target="_blank">overlapping</a> their home range with others of their species, even if they are of the same sex. Having said which, males occupy areas three times larger than females do, apparently because they want to meet as many members of the opposite sex as possible, while the females just want somewhere with a good food supply and somewhere nice to sleep. </div><div><br /></div><div>Like most skunks, it would rather not spray if it doesn't have to. Faced with a potential predator, its first inclination is to run away and hide. Stands of pricky pear cactuses are apparently a popular choice here, although, on rare occasions, they have been seen to <a href="https://doi.org/10.3398/064.070.0217" target="_blank">climb up a tree</a>. If this isn't an option, they will stand their ground, and may try to make themselves look bigger by standing up on their hind legs, and taking a few steps forward before thumping down on their forefeet and letting out a loud hiss. If even that fails to make their opponent think twice, they stamp on the ground and lay their tail flat against their backs before attacking with their spray, and, if necessary, a nasty bite. The spray has two of the same <a href="https://doi.org/10.1007/s00897990286a" target="_blank">primary components</a> as striped skunk spray, although a third major component is missing, and there are some <a href="https://doi.org/10.1007/BF00985013" target="_blank">differences</a> in minor chemicals that subtly alter the aroma (for all that that matters).</div><div><br /></div><div>At least in the US, the species <a href="http://hdl.handle.net/2346.1/30565" target="_blank">breeds</a> in February and March, but they are capable of sexual activity throughout the year, so this might be different further south. Litters are small, with typically no more than three kits, and singletons being common; they are born after a two-month pregnancy and leave home at around six months old.</div><div><br /></div><div>Contrary to the more common trend in recent decades, the American hog-nosed skunk was thought to represent two separate species through the 20th century, but <a href="https://doi.org/10.1644/1545-1542(2003)084%3C0159:TSOWBH%3E2.0.CO;2" target="_blank">research in 2003</a> showed that they weren't even distinct subspecies. Thus, many older sources refer to the animal as <i>C. mesoleucus</i>, with the current scientific name reserved only for those animals living along the west coast of the Gulf of Mexico. Although there was once some confusion around its more southerly relatives, too, they have been agreed to represent (at most) three species since the 1960s. More closely related to one another than to the "American" species, probably <a href="https://doi.org/10.1111/j.1096-3642.2008.00411.x" target="_blank">diverging</a> just after North and South America first joined up around 5 million years ago.</div><div><br /></div><div><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody><tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg0nI8Zo4xQDhlEJmk_z-Nil0HzLnWp4hmKESG-aryRXz8kIPohvm7_r_l6jFuJHxlwKcgsGlkhWYGDshfsEn2E0M8HzpQBGBDTfj-w2-8cg3zuaJk03w_HCToF7Z02YoEN9_9kkuYFpH9cWQTAYbRlGtaXB-TsqOYPJWMj0Y_QttyFw1anCfopF6aoN0I5/s312/Conepatus_semistriatus.jpg" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="253" data-original-width="312" height="253" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg0nI8Zo4xQDhlEJmk_z-Nil0HzLnWp4hmKESG-aryRXz8kIPohvm7_r_l6jFuJHxlwKcgsGlkhWYGDshfsEn2E0M8HzpQBGBDTfj-w2-8cg3zuaJk03w_HCToF7Z02YoEN9_9kkuYFpH9cWQTAYbRlGtaXB-TsqOYPJWMj0Y_QttyFw1anCfopF6aoN0I5/s1600/Conepatus_semistriatus.jpg" width="312" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">Striped hog-nosed skunk</td></tr></tbody></table>While the most distinctive feature of the "American" species is its lack of stripes (or single, very broad, white stripe, depending on how you look at it) this is obviously not true of the <b>striped hog-nosed skunk</b> (<i>Conepatus semistriatus</i>). This also lacks the white spot on the snout, and has small, but pig-like, nose for which the genus is named, but it has two white stripes along the back, separated by a black stripe down the middle. </div><div><br /></div><div>It lives from southern Mexico through Central America into Venezuela and Colombia and down the western side of South America as far as northern Peru. An isolated population also lives in eastern Brazil, separated from the rest of the species by the Amazon basin. This may sound odd, but until one was <a href="https://repository.si.edu/bitstream/handle/10088/20864/stri_2012_Esser_et_al_Small_Carnivore_Conservation.pdf" target="_blank">photographed</a> in Panama, it was also thought that the Mexican/Central American populations were also separated from the South American ones. What's probably happened here is that the species was more widespread during the Ice Ages, but the expansion of tropical forests at the end of that time split the Brazilian population off and it hasn't yet had time to evolve into an entirely separate species.</div><div><br /></div><div>This is because, like its more northerly relative, the striped species prefers grasslands and scrub as habitat, although it is also common in sparse woodland and stands of palm trees. While it has been spotted in denser Brazilian forest <a href="https://doi.org/10.1007/s42991-020-00056-4" target="_blank">in recent years</a>, this is likely due to a lack of alternatives as human development continues in the region, forcing them into habitat that they'd normally avoid.</div><div><br /></div><div>In most respects, their habits seem <a href="https://brill.com/view/journals/ab/64/2/article-p151_4.xml" target="_blank">similar</a> to those of the "American" species, although they are, perhaps, more thoroughly <a href="https://brill.com/view/journals/ab/67/2/article-p119_4.xml" target="_blank">nocturnal</a> and, while they do dig burrows in which to sleep, they may be less inclined to digging in general - perhaps with a less insect-based diet.</div><div><br /></div><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: right; margin-left: 1em; text-align: right;"><tbody><tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiHlXTlGF0ZNk9W5Zz1POu1tYXuHormyEtk5_nTURN2ay0z4xvw32UhYxoUsUN66MrZJjwTOHTs_bF5wIYd70Y5jcP_FumQWLAhdo1hMUXdcQiFRARmbtft1JbsJ37nS_58YqxGk7E5b-dqucxpON_1XRX56bIXqV9Xcyw9bj9IBSgpD4FrxFWdHXG29MTl/s400/Zorrillo_(Conepatus_chinga),_Uruguay,_2016.jpg" style="margin-left: auto; margin-right: auto; text-align: center;"><img border="0" data-original-height="400" data-original-width="321" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiHlXTlGF0ZNk9W5Zz1POu1tYXuHormyEtk5_nTURN2ay0z4xvw32UhYxoUsUN66MrZJjwTOHTs_bF5wIYd70Y5jcP_FumQWLAhdo1hMUXdcQiFRARmbtft1JbsJ37nS_58YqxGk7E5b-dqucxpON_1XRX56bIXqV9Xcyw9bj9IBSgpD4FrxFWdHXG29MTl/s320/Zorrillo_(Conepatus_chinga),_Uruguay,_2016.jpg" width="257" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">Molina's hog-nosed skunk<br /></td></tr></tbody></table><div>Further south, we come to <b>Molina's hog-nosed skunk</b> (<i>Conepatus chinga</i>), named for the <a href="https://en.wikipedia.org/wiki/Juan_Ignacio_Molina" target="_blank">Jesuit priest</a> and polymath who gave it its scientific name in 1782. It lives through much of mid-South America, from southern Peru, Bolivia, and <a href="https://doi.org/10.1590/S0073-47212012000300009" target="_blank">Brazil</a> in the north, through Paraguay and Uruguay into the more habitable parts of northern Chile and Argentina. It is slightly smaller than the striped species, <a href="https://doi.org/10.1016/j.mambio.2014.11.007" target="_blank">contradicting</a> Bergmann's Rule that animals in a given group should get larger as one approaches the poles. In general, though, it looks much the same, but with a variable coat pattern that often has a brown or even reddish background over the parts of the body one would expect to be black.</div><div><br /></div><div>Like its relatives, Molina's species prefers <a href="https://www.researchgate.net/profile/Carlos-Kasper/publication/258629766_Recent_advances_in_the_know_ledge_of_Molina's_Hog-nosed_skunk_Conepatus_chinga_and_Striped_Hog-nosed_skunk_C_semistriatus_in_South_America/links/00b49528bc867590bc000000/Recent-advances-in-the-know-ledge-of-Molinas-Hog-nosed-skunk-Conepatus-chinga-and-Striped-Hog-nosed-skunk-C-semistriatus-in-South-America.pdf" target="_blank">open terrain</a>, ranging from savannah in the north to cold steppelands in the south. It also has a similar diet, preferring invertebrates, with <a href="https://doi.org/10.1017/S0952836998251211" target="_blank">beetles and spiders</a> apparently being <a href="https://doi.org/10.1016/S0140-1963(03)00084-3" target="_blank">favoured foods</a>. Living outside the tropics, such food can be in short supply during the winter months, when its wider omnivory becomes more obvious as it eats more small mammals, birds, lizards, and frogs. They prefer to sleep in burrows during the day, whether they have dug them themselves or stolen them from other animals, but may use <a href="http://www.scielo.org.ar/scielo.php?pid=S0327-93832013000200009&script=sci_arttext&tlng=en" target="_blank">above-ground shelters</a> where the ground is too rocky for easy digging. Where possible, dens are <a href="https://doi.org/10.1515/mamm.2001.65.1.49" target="_blank">likely</a> to be in woodland or in rock piles at the bottom of cliffs, even if the skunks forage for food in more open grassland.</div><div><br /></div><div>Individuals occupy much larger home ranges than the other hog-nosed species. Females have been reported to occupy an average area of <a href="https://doi.org/10.1139/Z10-110" target="_blank">120 hectares</a> (300 acres) each, while males occupy areas <a href="https://doi.org/10.1016/j.mambio.2012.03.006" target="_blank">at least</a> twice that size (roughly one square mile). This may be due to a greater difficulty in finding suitable food, since they seem to spend more time searching for it than related species do.</div><div><br /></div><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody><tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgjgrZk8hchd7EVhdldvMtdFWcAXL8vYIWWp_eXVmSwEI6sF47sssSvZfRkOTGdU06PhC6jXRkqH4rsmZRfYVS30vXUiv9Kbv7xECZt21C23yajnlY4vpbUTCNblgVYPNnKWj0ba-vfYIF2LiETyiNZPfRP-UekPuEL7MLc_bkUoa41SPd3RDTxiTkyPMjk/s400/Zorrillo.jpg" style="margin-left: auto; margin-right: auto; text-align: center;"><img border="0" data-original-height="267" data-original-width="400" height="214" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgjgrZk8hchd7EVhdldvMtdFWcAXL8vYIWWp_eXVmSwEI6sF47sssSvZfRkOTGdU06PhC6jXRkqH4rsmZRfYVS30vXUiv9Kbv7xECZt21C23yajnlY4vpbUTCNblgVYPNnKWj0ba-vfYIF2LiETyiNZPfRP-UekPuEL7MLc_bkUoa41SPd3RDTxiTkyPMjk/s320/Zorrillo.jpg" width="320" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">Humboldt's hog-nosed skunk</td></tr></tbody></table><div>The same authors that recommended reducing the American hog-nosed skunk from two species to one also recommended <a href="https://doi.org/10.1111/zoj.12006" target="_blank">merging</a> the two most southerly species of the genus. In this case, however, the evidence is regarded as less clear-cut, and at least some current sources keep the two separate, thus maintaining <b>Humboldt's hog-nosed skunk</b> (<i>Conepatus humboldtii</i>) as a distinct species. Looking very similar to Molina's species, it is found only in Patagonia, across southern Argentina and Chile as far as - but not beyond - the Straits of Magellan. </div><div><br /></div><div>It seems to be less of a habitat specialist than the more northerly species, being more willing to live in wooded areas as well as grassland. They seem less keen on digging for themselves, denning in pre-existing spaces where possible, such as hollow trees, shallow caves, and even the spaces beneath log piles and inhabited buildings. While they prefer to prey on invertebrates such as beetles, crickets, and spiders, they consume a higher proportion of <a href="https://doi.org/10.1007/BF03192421" target="_blank">carrion</a> than their kin, especially during the winter and also feed at human refuse piles. Perhaps because of the cold nights, they are more crepuscular than nocturnal and are often seen during the day as winter approaches - likely spending more time searching for food so that they can build their reserves up for months when heavy snowfall may make foraging impossible.</div><div><br /></div><div>With that, I have covered every species of skunk from Canada to the edge of the Antarctic Ocean and included everything that would have been considered a skunk for most of the 20th century. But it turns out that the animals we actually call "skunks" are not the only members of the skunk family as we now understand it. So, to complete the survey of that family, I will have to head somewhere else entirely...</div><div><br /></div><div><i>[Photos by <a href="https://www.inaturalist.org/users/5772" target="_blank">Juan Cruzado Cortés</a>, <a href="https://commons.wikimedia.org/wiki/File:Conepatus_semistriatus.jpg" target="_blank">Washington L.S. Vieira</a>, <a href="https://www.wikidata.org/wiki/Q90236211" target="_blank">Enrique González</a>, and "<a href="https://www.flickr.com/people/payayita/" target="_blank">Payayita</a>", from Wikimedia Commons.]</i></div></div>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com1tag:blogger.com,1999:blog-4209921721314660731.post-31984924741364436082023-09-30T16:05:00.000+01:002023-09-30T16:05:39.369+01:00Hammer-Toothed Snail Eaters<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhR1NL3FTL7U8pDdTXPLI_SIoFmTdeInf-l7YRHLOtdh9ei_hsUlG5L8s0rJ5l4qwujPeTq3ArRCPGpNr2U1TgHFcMseJgOOhASYL3FBnpmFKo_1UTzW3c-nOKKYLmbPaGS5LDLuwAqgJthboM99jzfqCWTptigHc7liDWJpVQgtvUK9dGY-w-rkJjv0mEa/s400/800px-Weinbergschnecke1.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="320" data-original-width="400" height="256" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhR1NL3FTL7U8pDdTXPLI_SIoFmTdeInf-l7YRHLOtdh9ei_hsUlG5L8s0rJ5l4qwujPeTq3ArRCPGpNr2U1TgHFcMseJgOOhASYL3FBnpmFKo_1UTzW3c-nOKKYLmbPaGS5LDLuwAqgJthboM99jzfqCWTptigHc7liDWJpVQgtvUK9dGY-w-rkJjv0mEa/s320/800px-Weinbergschnecke1.jpg" width="320" /></a></div>As is true of mammals more generally, the majority of Australian marsupial species are herbivorous, including such familiar animals as kangaroos, wombats, koalas, and possums. (The latter, of course, are not to be confused with the American opossums, which are omnivorous and not very closely related to their Australian namesakes). Most, but not all, of those that are not belong to a single order, the dasyuromorphs, sometimes called the "carnivorous marsupials" for this reason.<p></p><p>Although they represent almost a third of non-American marsupial species, dasyuromorphs are far less diverse than their herbivorous counterparts, with all but one of the living species belonging to a single family, the dasyurids. Although the most famous example of the dasyurids is probably the Tasmanian devil, which eats comparatively large prey, most of the other species are small shrew-like animals feeding on insects. Alongside them, we can place the numbat and the extinct thylacine ("Tasmanian tiger" or "wolf") both of which are odd enough to be placed in families of their own.<span></span></p><a name='more'></a><p></p><p>Fossil dasyuromorphs are not common, but they do exist, with most of them discovered at the same Riversleigh deposits that many other fossil marsupials have been. Most of these fossils are sufficiently well-preserved that we can place them into one of the two living subfamilies of dasyurid and we know of at least seven species of <a href="https://doi.org/10.1017/S0022336000038737" target="_blank">fossil thylacine</a>. There are, however, a few fossil species from the site that we just can't place into any of the living families, whether because of incomplete remains, or because they're too primitive to make an easy decision either way.</p><p>Or because they're really weird.</p><p>Such is the case for <i><b>Malleodectes</b></i>, <a href="https://doi.org/10.1098%2Frspb.2011.0486" target="_blank">first described</a> in 2011 from a partial upper jaw that was around 12 to 15 million years old. That original paper classifies it as "Metatheria <i>incertae sedis</i>" which loosely translates as "we think it's a marsupial, but beyond that, we're stumped". In fact, the researchers say that, if the roots of the teeth had not been obviously mammalian in form, they might have thought it was a skink.</p><p>So what was so odd about it? It had three premolars, which is what you'd expect of most marsupials, so nothing odd there, but the last of those premolar teeth was anything but normal. For one thing, it was huge, with twice the diameter of any other teeth in the jaw. This is what made it look like a lizard, because certain skink species do have an exceptionally large tooth in roughly that position of the jaw. Moreover, the tooth in question had no blade, having a domed shape like a <a href="https://en.wikipedia.org/wiki/Ball-peen_hammer" target="_blank">ball-peen hammer</a> so that it couldn't plausibly have cut anything. It also had four roots, something never seen before in any marsupial, implying that whatever it was used for required considerable bracing.</p><p>Thus, the scientific name <i>Malleodectes mirabilis</i>, which translates as "extraordinary hammer-biter". A second species, <i>M. moenia</i>, was named at the same time, but remains known from only a single tooth. In 2016, a more complete upper jaw of the first species was described, giving a clearer view of the molar teeth behind the strange one and it was this that led to the researchers deciding that it was <a href="https://doi.org/10.1038/srep26911" target="_blank">probably</a> a dasyuromorph. That it was still very odd meant that it clearly didn't belong in any of the three known families and it was accordingly given its own one - the only recognised dasyuromorph family other than the three that survived into historical times.</p><p>And that has been the status for the last seven years - two pieces of upper jaw and one isolated tooth, belonging to two species between them, in a rather uncertain evolutionary position relative to more conventional marsupials. To learn more about these odd creatures, we'd need more specimens, preferably from some other part of the body. Which is now <a href="https://doi.org/10.1080/02724634.2023.2170804" target="_blank">what we have</a>.</p><p>A significant issue is that the new specimens - and there are two of them - consist only of sections of lower jaw. That means there's no overlap between them and the older specimens; nothing that we can see in both that means we can definitely say "yes, these belonged to the same sort of animal". </p><p>Indeed, these two pieces of jaw can't possibly belong to either of the known species, because they're far too small. Clearly, it's difficult to get a good estimate of the body size of an animal when all you have is a few bits of jaw, but there are at least some methods of guessing based on the proportions of other animals. Using <a href="https://doi.org/10.1071/ZO01009" target="_blank">a formula</a> devised specifically for marsupials, the researchers estimated that the animal their new fossils belonged to weighed around 90g (3 oz.) - about twice as much as a house mouse. There's a lot of uncertainty in this, but using the same formula on <i>M. mirabilis</i> indicates that that would have weighed around 900g (2 lb.), similar to a hedgehog. </p><p>It's pretty clear that those are not going to be the same species. But what the new specimens do both have is a greatly enlarged, dome-shaped, second premolar similar to the giant tooth on the upper jaws of the previously known species. The third lower premolar has the same unusual shape as well, although it is more normal in size. That seems good evidence that the new animal is a close relative, although whether it's a new example of <i>Malleodectes</i> itself, or some new genus in the same family, isn't something we can say with certainty until we can get a pair of jaws that actually match.</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjN4YwasCsySkoxnmlibvDROniwEN-cOJ1ggQkALHSoGd72vLm3LAnL5-75Xk2e3cPnKGPTb73TQXVC9uwix2p6N9Es9Y0_qgYMYOyBDiU9FO-zR5fuK8jJ8I03peYLyZa76BC8aAHVmxK548nmwko_ldpo4udn1AQ00rNSjln4bUkwzZgvoA3E3_wBLk8D/s400/Dasyuromorpha.JPG" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" data-original-height="277" data-original-width="400" height="222" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjN4YwasCsySkoxnmlibvDROniwEN-cOJ1ggQkALHSoGd72vLm3LAnL5-75Xk2e3cPnKGPTb73TQXVC9uwix2p6N9Es9Y0_qgYMYOyBDiU9FO-zR5fuK8jJ8I03peYLyZa76BC8aAHVmxK548nmwko_ldpo4udn1AQ00rNSjln4bUkwzZgvoA3E3_wBLk8D/s320/Dasyuromorpha.JPG" width="320" /></a></div>But, if we can't compare the lower jaw of this smaller malleodectid with those of the previously known species, we can compare it with those of other carnivorous marsupials. Performing that analysis on the same basis as a <a href="https://doi.org/10.1186/s12862-017-1090-0" target="_blank">2017 study</a> looking at the whole group gives strong backing evidence that the creature is, indeed, a dasyuromorph that belongs to none of the modern families. Specifically, it turns out to be a very close relative of the dasyurids, far more closely related to them than to the numbats or thylacines, but still not quite within the group.<p></p><p>This leaves the question of what exactly <i>Malleodectes</i> was eating that required it to have uniquely shaped teeth. The hammer-like teeth suggest that the animal was trying to crack something, rather than tearing flesh, and the lower jaw appears too slender for it to have resisted the stresses that would be caused by struggling prey. It could have been a scavenger, cracking bone like a miniature hyena, but, if it were, we'd expect the other teeth to be modified for chewing up the fragments - as they are in both hyenas and Tasmanian devils.</p><p>By rescaling the jaws from the two different species so that they're the same length, and lining them up against each other, it now appears that the huge upper tooth would have crushed food against the two teeth behind the enlarged ones in the lower jaw, and those would have engaged with the canines and first premolars in the upper. That makes the crushing surface longer than we had previously thought, a bit like a nutcracker. Every other indication is that it was a carnivore, however, so nuts may also have been off the menu.</p><p>This basically leaves us with the theory originally proposed when the first fossil was discovered, and that compares it to the diet of the <a href="https://en.wikipedia.org/wiki/Pink-tongued_skink" target="_blank">pink-tongued skink</a>, a lizard with similar-looking teeth. That mainly eats slugs and snails, and it uses the hammer-shaped teeth to crush snail shells, with the rest of the prey animal being soft enough that it doesn't need the modifications we'd see in a bone-crusher. While this new fossil belonged to a species much smaller than the previously known ones, that hardly disqualifies it from eating snails.</p><p>While there are some mammals, such as certain kinds of otter, that specialise in eating shellfish, one that feeds primarily on snails would be an oddity. But, while we can't be certain, it remains the best bet for what this peculiar little marsupial was up to.</p><p><i>[Photo by <a href="https://commons.wikimedia.org/wiki/User:Pascal_Abel" target="_blank">Pascal Abel</a>, from Wikimedia Commons. Cladogram adapted from <a href="https://doi.org/10.1080/02724634.2023.2170804" target="_blank">Churchill et al. 2023</a>.]</i></p>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com0tag:blogger.com,1999:blog-4209921721314660731.post-19479282484840814082023-09-24T17:34:00.002+01:002023-09-24T17:34:21.918+01:00Return of the Rabbits?<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody><tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj21zjjhU4IdcfcV_5_yy4kDYQMVIaDxrB-gEoG2EH0bcxKzl62ubIVvT4H5faACcv_DYgDvN_0FI2UOXuyy4DnZAY_1XXFrWdllGoQkQ5UbRCxNcCeFAdmCrOdcsZNbDFlwcGkoTl9wss3Cdg1hpgqcbiziyQVaQ-2j11HRkdxJdm2vbVUczZkKN6-c5DL/s400/Sylvilagus_transitionalis_(21315229532).jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="311" data-original-width="400" height="249" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj21zjjhU4IdcfcV_5_yy4kDYQMVIaDxrB-gEoG2EH0bcxKzl62ubIVvT4H5faACcv_DYgDvN_0FI2UOXuyy4DnZAY_1XXFrWdllGoQkQ5UbRCxNcCeFAdmCrOdcsZNbDFlwcGkoTl9wss3Cdg1hpgqcbiziyQVaQ-2j11HRkdxJdm2vbVUczZkKN6-c5DL/s320/Sylvilagus_transitionalis_(21315229532).jpg" width="320" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">This one is wearing a radio collar...</td></tr></tbody></table>It's abundantly clear that humans have had a dramatic effect on the number and distribution of animals across the globe. (For that matter, by some measures, plants may be doing even worse). There are great swathes of the world where particular animals were once common but are not so any more. Just to take a dramatic and obvious example, Great Britain used to be home to wolves and bears but we don't see those around any more. Those are, of course, widespread elsewhere, but other animals may be less lucky.<div><br /></div><div>In some places, however, a key method in conservation may be reintroduction, bringing animals back to their native habitat, either from elsewhere, or directly from captive populations. This can help restore natural ecosystems, with the return of one originally native species <a href="https://doi.org/10.1098/rstb.2008.0335" target="_blank">helping others</a> that are now in decline, but have yet to disappear altogether. Again taking Britain as an example, there are currently efforts underway to <a href="https://doi.org/10.1111/j.1365-2907.2010.00167.x" target="_blank">reintroduce beavers</a> to the country, where they have been locally extinct since the 16th century. Similar programs for other animals exist elsewhere, but the reality is that such efforts are not always successful.<span><a name='more'></a></span></div><div><br /></div><div>This can happen for <a href="https://doi.org/10.1016/S0006-3207(00)00048-3" target="_blank">various reasons</a>, some of which are simply financial or organisational. But the most common are the animals simply fail to thrive, perhaps because they get <a href="https://doi.org/10.1016/j.biocon.2011.08.003" target="_blank">eaten</a> by predators they are no longer used to, or because the <a href="https://doi.org/10.1111/aec.12017" target="_blank">habitat</a> is no longer as suitable as we had hoped. Obviously, if we are going to perform reintroductions, we'd like to know how well they're doing, or whether it was all a wasted effort - and, if so, how we can do better next time. Despite this, <a href="https://museucienciesjournals.cat/abc/issue/43-2-2020-abc/a-global-review-of-animal-translocation-programs.pdf" target="_blank">a 2020 review</a> of such programs found that, in around half of cases, there doesn't seem to have been any follow-up to answer this question.</div><div><br /></div><div>A major reason for this may be that it takes a lot of time. If you want to know whether your reintroduced animal has reproduced and established a stable population... well, you have to wait for it do so (or not). And that can take years, especially if the animal is slow-breeding. But perhaps there are some pointers we can use early on in such programs to give us some idea of how things are going.</div><div><br /></div><div>The <b>New England cottontail</b> (<i>Sylvilagus transitionalis</i>) once lived across the whole of New England, save only for the most northerly parts of Maine, as well as in New York state east of the Hudson. It's one of nine species of cottontail rabbit native to the US, along with many more in Latin America, constituting a well-defined group closely related to, but distinct from, the various Old World species. Most of the other US species are doing well, with large, often stable, populations... but not so the New England one.</div><div><br /></div><div>It is thought that the species now inhabits <a href="https://doi.org/10.1002/wsb.1140" target="_blank">less than a sixth</a> of the area it did in 1960, with the US Fish and Wildlife Service estimating the total population at no more than around 17,000, over half of which are divided between two regions in northwestern and southeastern Connecticut. Over half of the remainder live in the Cape Cod area of Massachusetts, with smaller, isolated populations in limited parts of Rhode Island, New Hampshire, Maine, and on Nantucket. So far as is known, it has entirely vanished from Vermont, <a href="https://doi.org/10.1002/ece3.4580" target="_blank">replaced</a> there, as elsewhere, by the almost identical-looking eastern cottontail (<i>S. floridanus</i>) which inhabits essentially the entire eastern half of the US but was not originally native to New England.</div><div><br /></div><div>As a result of this, the New England cottontail is internationally listed as a "threatened" species and is considered "endangered" under state law in New Hampshire and Maine. Elsewhere, since the same isn't true under federal law, it remains legal to hunt them, and, in any event, it's next to impossible to distinguish them from the non-protected eastern cottontails. Furthermore, the rabbit's natural habitat is relatively narrow; it prefers low shrubland and avoids both open terrain without cover and denser patches of woodland. Shrubland is declining in New England, partly due to a growth in closed-canopy forests on abandoned farmland as well as the loss of the original shrubland to farms that are still functioning, not to mention roads and urban expansion.</div><div><br /></div><div>To counteract this, there have been several attempts to reintroduce the rabbits into the remaining suitable parts of their former range where they have nonetheless disappeared. As with other animals, these programs have had only mixed success. One possible way to get an early hint of whether a given program is likely to succeed or not is to see how the rabbits <a href="https://doi.org/10.1111/acv.12534" target="_blank">behave</a> after they are released. To do that, we also need to build up a picture of how they behave normally, so this is exactly what a <a href="https://doi.org/10.1093/jmammal/gyad023" target="_blank">recent study</a> did.</div><div><br /></div><div>In some respects, this is a lot easier to do today than it would have been a couple of decades ago. This particular study fitted the rabbits it was following with GPS collars that could record their precise location but that also includes triaxial accelerometers, able to collect detailed data about the precise speed, acceleration, and direction of their movements. That sounds a lot, but the collars only weigh 20 g (⅔ oz.) which is far less than the roughly 1 kg (2 lbs 3 oz.) weight of the rabbit, so likely noticeable, but not too inconvenient for the animal. </div><div><br /></div><div>The first part of the study involved doing this with rabbits in a captive breeding program at Queens Zoo, allowing the researchers to monitor them with video cameras and ensure that the readings they got from the accelerometers could be matched precisely to particular activities. Once they could confidently say what a rabbit was likely to be doing by looking at the recorded data, they repeated the experiment with wild-caught rabbits immediately released back into their home and with both wild and captive-born rabbits reintroduced to a couple of wildlife refuges in southern Rhode Island.</div><div><br /></div><div>There are some limitations to this in that some activities may involve movements that are hard to differentiate - eating grass and sniffing at the ground to investigate it, for instance. But this has been <a href="https://doi.org/10.3389/fevo.2019.00154" target="_blank">done before</a> with different animals, and these issues are reasonably well-known and can be accounted for.</div><div><br /></div><div>The results showed, unsurprisingly, that all of the rabbits spent most of their time doing relatively little - resting, watching out for predators, and grooming themselves. These are all activities that can be performed while hiding under a bush or in the sort of dense undergrowth that this species favours, and similar behaviour can be seen even <a href="https://doi.org/10.1007/s10531-016-1134-6" target="_blank">among predators</a> in human-dominated areas. However, the rabbits introduced to new sites as part of the reintroduction program spent even more time than those in their home area watching for danger and also spent a lot of time exploring their new habitat. The difference in behaviour between the wild rabbits that had been moved elsewhere and those that had been bred in captivity was relatively minor, although the researchers argue that there may have been a slight bias towards (possibly nervous) exploration among the captive-born ones.</div><div><br /></div><div>Again, this is probably not a great surprise, although it's certainly useful to be able to prove it, and, more importantly, to quantify how much it happens. That the captive-bred rabbits aren't at a disadvantage, at least in the short term, is also reassuring. The thing about exploration, though, is that you obviously <i>can't</i> do it while hiding. The mere act of exploration not only uses up some of the rabbits' energy resources, requiring them to eat more to keep their strength up, but exposes them to predators. Yet they have to do it, if only to find where food sources might be and where the best locations for hiding are.</div><div><br /></div><div>This greater exposure to risk may help explain why reintroduction efforts for this species have had only patchy success. It's a well-known problem for efforts with <a href="https://doi.org/10.2193/2006-141" target="_blank">other species</a>, but it does provide some pointers for how we might improve things going forward. If you can give the rabbits some time to acclimatise to their new home before being fully released, that might help. Another <a href="https://doi.org/10.1016/j.biocon.2011.04.027" target="_blank">suggestion</a> is providing them concealed feeding stations that they can use until they get used to their new home, cutting down on the need for exploration - although that's going to be a problem if predators figure out where the stations are and stalk nearby like lions at a watering hole. </div><div><br /></div><div>But, either way, using techniques like this to understand what captive animals do once reintroduced into the wild can at least give some advance warning of how likely a given project is to succeed, and give conservationists a chance to do something about it before it has already failed.</div><div><br /></div><div><i>[Picture credited to the <a href="https://www.flickr.com/people/42687493@N06" target="_blank">US Department of the Interior</a>, from Wikimedia Commons.]</i></div>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com0tag:blogger.com,1999:blog-4209921721314660731.post-10388416378958667142023-09-17T16:53:00.000+01:002023-09-17T16:53:42.382+01:00We're Up All Day to Get Lucky<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgMSJmijYAg_BmawT5nhoqSCSjl5bsGubnVhWKJIJgGxswtJPDfo7ne_3PPGQW7uHmpwCzasGfQhSde-VkI5Jo-CczToqmxe64yf2fnbS4MH0tdT47lP7prTjQ6ScyOOVYgLXyPCReZJ-St9hU-lZxBINbydH8dPvzWwXsVevOtD8ErNp-RfGnKadXHRq1d/s400/Lobo_ib%C3%A9rico.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="400" data-original-width="296" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgMSJmijYAg_BmawT5nhoqSCSjl5bsGubnVhWKJIJgGxswtJPDfo7ne_3PPGQW7uHmpwCzasGfQhSde-VkI5Jo-CczToqmxe64yf2fnbS4MH0tdT47lP7prTjQ6ScyOOVYgLXyPCReZJ-St9hU-lZxBINbydH8dPvzWwXsVevOtD8ErNp-RfGnKadXHRq1d/s320/Lobo_ib%C3%A9rico.jpg" width="237" /></a></div>One of the key characteristics that's often listed for the behaviour of a mammal species is what time of day it tends to be active. There are four basic options here, of which the most obvious are diurnality and nocturnality. The others are crepuscularity if it's most active around dawn and dusk but not in between, and cathemerality if it really doesn't care - often because it lives underground. But, either way, it's natural to assume that this behaviour is relatively fixed in an animal; either it's nocturnal or it isn't.<p></p><p>In reality, however, it turns out that this can have a lot to do with the circumstances. And, in the modern world, those circumstances are most likely to be shaped by... what else, but humans? </p><p>The issue, of course, is that humans are for the most part diurnal. Which isn't much of a problem for animals that are naturally nocturnal, but can be if they, too, would prefer to be active during the daylight hours. What we see time and time again across the world, and across different mammal species, is that where humans are most likely to encounter wild animals, those animals shift their behaviour towards nocturnality to avoid the stress of meeting us too often.<span></span></p><a name='more'></a><p></p><p>To be sure, it's not a universal rule, and it probably applies more to large animals that we might hunt than it does to smaller ones that can stay out of sight or hide in our cornfields. But one study in 2018 looked at 62 medium to large mammal species from across the globe, ranging from coyotes to deer, lemurs, elephants, and porcupines and concluded that in areas with high "human disturbance", on average these animals were <a href="https://doi.org/10.1126/science.aar7121" target="_blank">over one third</a> more likely to be active at night than they would otherwise.</p><p>What sort of "human disturbance" you might ask? Well, the study showed that it really didn't matter. You might think that actively being hunted or persecuted would be the biggest driver of switching to nighttime behaviour but it turns out that simple agriculture and even living in a wild area frequented by hikers have just as much of an effect. Not to mention that living near a busy road is quite possibly as deadly to a wild animal as being on the hunting menu. Nor, at least from this study, did it seem to matter whether the animal was a predator or a herbivore, although the largest and most visible animals did seem to be more strongly affected than the others.</p><p>There is, on the other hand, a flip side to this. Things like agriculture and road building are expanding across many parts of the world, and leading to declines in many animal populations. But, in recent decades, the pattern of human development has tended to follow a different path in Europe and North America than elsewhere. Here, we see increasing urbanisation, something that clearly brings its own problems, but that does have the effect of <a href="https://doi.org/10.1111/ruso.12266" target="_blank">depopulating rural areas</a>. This means that, outside of those concentrated urban areas, wildlife is <a href="https://doi.org/10.1016/j.biocon.2020.108860" target="_blank">less likely</a> to encounter humans, and can reassert its preferred behaviour. </p><p>This isn't merely theoretical. Eurasian otters, for example, used to be nocturnal where humans were present, but researchers can now sit around and <a href="https://doi.org/10.2981/wlb.00589" target="_blank">watch them fishing</a> even in artificial reservoirs. An additional factor here may be that our relatively urbanised, modern, populations are likely to see wild animals less as competitors or threats to livestock but as something to be preserved and cherished.</p><p>But those changing attitudes and population shifts may only go so far. It's one thing to reduce the threat to, say, deer or badgers but it might be another to change the attitudes of the people who still do live in rural areas to animals they see as an active threat. In many parts of North America and Europe, one of the prime examples of this is surely the <b>grey wolf</b> (<i>Canis lupus</i>).</p><p>Wolves have been persecuted throughout human history, seen as a menace to our livestock and even to humans directly. Frankly, it's a wonder we ever domesticated them; in the wild we've done pretty much everything we can to get rid of them. The last wolf in the British Isles is generally said to have been killed in 1680, although later claims exist. Of course, there we had the advantage of being an island, making it difficult for new wolves to wander in to replace those killed.</p><p>The French had no such advantage when it came to wiping out all the wolves in their country, but that didn't stop them trying. Charlemagne set up the <i>louveterie</i>, a specialised corps of wolf-killers, in the early 9th century. It took them over 1,000 years (handicapped by being briefly abolished after the Revolution) to finish the job, but they finally managed it in the 1930s. Even then, in an example of our changing attitudes to such things, wolves were granted legal protection in the country in 1993, a year after one was spotted sneaking across the Italian border into the Mercantour National Park just north of Nice. There are now thought to be about 500 wolves living in France, mostly around the Alps.</p><p>There are similar stories from other parts of Europe, with the Balkans and Carpathian Mountains having held on to the largest populations. In western Europe, the largest surviving population is probably that in Spain, where it is estimated that there could be as many as 2,000, living in about 350 packs, all in the northwest of the country. Some researchers describe these as a <a href="https://doi.org/10.1111/j.1469-7998.2000.tb00801.x" target="_blank">distinct subspecies</a> (<i>Canis lupus signatus</i>) as they diverged from the Italian population <a href="https://doi.org/10.1098%2Frspb.2020.1206" target="_blank">10,300 years ago</a> around the end of the Last Ice Age, but, even if they don't quite earn that honour, they are genetically distinct.</p><p>Despite their comparatively large numbers, wolves have been persecuted just as much in Spain as in other countries. Legal protection was only brought in at a national level in <a href="https://www.spainenglish.com/2021/02/05/hunting-iberian-wolves-banned-spain-farmers-protest/" target="_blank">2021</a> (it was earlier in Portugal, but there is only a tiny remnant population there, along the northern border) and there are efforts from some political parties to <a href="https://www.reuters.com/world/europe/iberian-wolf-crosshairs-spanish-right-parties-court-rural-voters-2023-07-04/" target="_blank">reverse</a> that. So one would expect that Spanish wolves, like those elsewhere, are probably still cautious and try to avoid angry farmers with guns - and humans more generally - as much as they can.</p><p>Would they behave differently if there were no humans around to bother them or they naturally nocturnal anyway? It's the sort of thing that's difficult to test. We'd need two sizable areas, relatively close to one another, in one of which humans are present, doing the sorts of things they normally do, and in one of which human presence is essentially banned. The best example of the latter in recent years is probably the area around Chernobyl, but there are sound reasons why it's difficult to do too much wildlife research there. </p><p>A <a href="https://doi.org/10.1093/jmammal/gyad003" target="_blank">recently published study</a>, however, took a look at the wolves living in a smaller and less dramatic example of such an area in the north of Spain. The As Pontes coal mine was closed in 1985 and, over the next 20 years, the debris dump around it was rewilded by planting native vegetation and fencing it off to prevent human access. The process was completed in 2009, leaving a 1,120-hectare (4.3 square mile) <a href="https://www.google.com/maps/place/Parc+National+Mercantour/@43.4586544,-7.9546353,8576m/data=!3m1!1e3!4m6!3m5!1s0x12cdaf6678af879d:0xcabc15aee7b89386!8m2!3d44.1308825!4d7.0936255!16zL20vMDhma24x?entry=ttu" target="_blank">area</a> that it is difficult - and generally forbidden - for humans to access, but that animals can still enter. It is now home to several deer, wild boar, foxes, and, yes, wolves.</p><p>Using camera traps and checking their results by radio-tagging a couple of wolves and following their movements on GPS, the researchers began by looking at a more typical area to the south, a hilly region occupied by a mix of cattle pasture, scrubland, and pine plantations. Here, the wolves were, as we'd expect, nocturnal, spending 80% of their activity time between the hours of 8 pm and 8 am. This fits with how we'd generally expect wolves to act, consistent with other studies that show wolves as a generally nocturnal animal - for example, in <a href="https://doi.org/10.1007/s10344-005-0111-2" target="_blank">Croatia</a> and <a href="https://doi.org/10.2193/0022-541X(2006)70[1079:LUAMOW]2.0.CO;2" target="_blank">Minnesota</a>. </p><p>So, nothing unusual about Iberian wolves compared with those elsewhere, then. But, when it came to look at them, it turned out that the wolves living at the human-restricted nature reserve were not the same. While they were often still active at night, they continued their activity right through the morning, not going to sleep until around 2 pm, and actually being most active shortly before noon. Not really what you'd expect from a "nocturnal" animal.</p><p>It's plausible that, as predators, part of the reason for this shift in wolf behaviour was due to the local deer being less afraid of hunters, and therefore more active during the day themselves. The wolves were clever enough, for instance, to sneak out of the nature reserve at night to hunt the feral horses in the surrounding terrain, and then slink back again before dawn. But, on the other hand, they did seem relatively unafraid of humans (such as the researchers) on their home ground so it's likely that they're simply more comfortable being awake in the morning if only people aren't going to try and shoot them. Plus, the local deer and wild boar, unlike the wolves, are culled from time to time so they may still prefer coming out at night when they can.</p><p>The site had been fenced off for nine years at the time of study, so we don't know how long it took for the wolves to adapt to their new freedom. But the researchers point out that wolves were sometimes seen prowling Italian streets <a href="https://doi.org/10.1016/j.biocon.2020.108728" target="_blank">in broad daylight</a> during the COVID lockdowns, so it may be quite quick. </p><p>Few places are as free from humans as a fenced-off nature reserve but the general depopulation of rural areas across much of western Europe, not to mention any hunting bans that might be coming into place, may well be good news for wolves across the region. Quite how humans might react if they saw wolves around more often during the day and realise that the animals are more common than they thought is another matter. It is not, after all, as if wolves are entirely harmless, and those who wish to, for example, photograph them in the wild might not be in a majority. </p><p>How we manage those expectations and provide safety for those still living in or travelling through depopulated rural areas might be something we have to think about in the coming decades.</p><p><i>[Photo by <a href="https://en.wikipedia.org/wiki/File:Lobo_ib%C3%A9rico.jpg" target="_blank">Tudela de Duero</a>, from Wikimedia Commons.]</i></p>JK Revellhttp://www.blogger.com/profile/00358838350092883422noreply@blogger.com1