Moulting Marmots

Moulting is a feature of mammalian physiology that will be familiar to pet owners worldwide. While it's not present in all mammals, it is very widespread despite the fact that, when you think about it, it's obviously costly to the animal in question. Why shed and replace a large amount of hair in a short time when you could replace it bit by bit as humans do?

The fact that so many mammals, of widely different kinds, moult to at least some extent shows that it must be an evolutionary ancient phenomenon. In fact, it turns out that animals have probably been moulting since before they even had hair. We can tell this because it's not unique to mammals. For instance, birds moult their feathers, and the process is similar to hair moulting in mammals. More significantly, perhaps, moulting has the same underlying mechanisms as reptiles periodically shedding their skin and can be tied back to sloughing in fish and amphibians as well. 

You Scratch My Back...

One of the most widespread behaviour patterns among non-human primates is their habit of grooming one another. Technically referred to as "social grooming" or "allogrooming", this refers to cleaning the fur of other animals, removing ticks and other parasites. In addition to the obvious health benefits, this also helps maintain cohesion among social groups that can be structurally complex. Indeed, it's generally thought to be one of the main reasons primate societies are so sophisticated in the first place.

Many mammal species live solitary lives, at least outside of the mating season. For those, there would be little opportunity for social grooming and no wider benefit to be gained from it if there was. Self-grooming or "autogrooming" - such as licking one's own fur - may well be sufficient for them. But, of course, primates are not the only social mammals, and many of those other animals have fur in which parasites could hide, so it's reasonable to ask if allogrooming really is unique to primates.

Antilopine Antelopes: Dwarf Antelopes of Eastern and Central Africa

Oribi

The term "dwarf antelope" can reasonably be applied to many different kinds of antelope that are smaller than, say a typical goat. In this common sense, it's not a precise term, and could refer to species that belong to quite different branches of the antelope family tree. When mammalian zoologists used the term in the 20th century, however, it was often more precise, referring to those thought to be most closely related to the gazelles as a branch within the "antilopine" subfamily of "typical" antelopes.

Technically, these dwarf antelopes were collectively referred to as "neotragines" and assumed to be a natural grouping within the antelopes more widely. Genetic analysis over the last couple of decades has muddied these waters considerably, not least because the genus for which the branch was named, Neotragus, turns out not to be closely related to the gazelles, and is something else entirely. Even if we look solely at those dwarf antelopes that we can still say belong to the antilopine subfamily, it turns out that they don't have a single common ancestor. Specifically, one of them is more closely related to gazelles than it is to any of the other members of its purported evolutionary branch. 

Oligocene (Pt 11): Early Monkeys and Two-Ton Herbivores

Arsinoitherium

Because the Oligocene is so much further back in time than the later epochs, especially the Pliocene and Pleistocene, there are more gaps in our knowledge of it. That it's also much shorter than the epochs to either side of it means that those gaps can, proportionately speaking, occupy far more of its length. One of the places where such a gap is particularly noticeable is the history of primates.

Monkeys first appeared in Africa in the latter half of the preceding epoch, but their early record is patchy. This is likely because many of the earliest monkeys lived in areas that simply weren't conducive to forming fossils - although the fact that many parts of Africa have not had the same detailed paleontological surveys that other continents have may also be a factor. Much of the history of the primates during the epoch is a blank... but not entirely.

700th Synapsida

Well, here we are again with another biennial look-back at the last 100 posts, highlighting what may have been missed and taking a brief peek at where I might go next. I can't say it's entirely gone without a hitch over the last couple of years, but I've mostly kept to the weekly schedule... although you might get more regular gaps in the summer going forward.

Evolution remained the single most common category for the past 100 posts, which is hardly surprising given how many are about extinct species, and how important it can be to understanding how the living ones got to be the way they are. However, diet and habitat, which are often linked, have overtaken animal behaviour to nab the second and third spots... although the latter has remained common. Since I pick most topics on the day, without any grand plan to even things out, that's probably just the vagaries of what I happen to have come across. 

Hair, Fur, Bristles, and Spines

Trinomys

Hair is one of the key defining features of mammals. Apart from cetaceans, such as dolphins, no mammals are entirely hairless, although, for example, hippos and some babirusa species come very close. The original purpose of hair was almost certainly to maintain body heat, something that matters to warm-blooded animals in a way that it doesn't to, say, reptiles. Since then, however, hair has adapted to fulfil many other functions as well.

To begin with, there is colouration, a function that hair needs to take over once it obscures the skin. The most obvious way that hair colour can help an animal is camouflage. While this is instinctively true, there have been statistical studies that demonstrate certain hair colours are, indeed, more common in animals living in certain environments. For instance, multi-species analyses of lagomorphs and cloven-footed mammals have shown that animals with grey fur are more likely to live in rocky environments. The same studies, as well as similar ones on carnivores, show that pale fur is associated with open environments, especially deserts, while dark fur is most common in those animals living in jungles, dense forests, or heavily vegetated swamps. And, surely to the surprise of almost nobody, white fur is associated with the Arctic, or with the winter coats of those living where it snows.

Antilopine Antelopes: Dwarf Antelopes of southern Africa

Steenbok

The "antilopine" subfamily of antelopes, so named because it happens to include the first animal scientifically described as an antelope rather than a goat, is itself divided into at least two major branches. There may or may not also be minor ones, depending on what you think is worthy of naming, but the two main ones are quite clear, and perhaps separated from one another around 12 million years ago towards the end of the Middle Miocene.

One of these groups contains the gazelles, along with the springbok, some other gazelle-like animals, and that "first" antelope mentioned above, the blackbuck. These are, for the most part, smallish slender, fast-running antelopes living in arid or semi-arid habitats in both Africa and Asia. The second group are the dwarf antelopes, found only in Africa and quite visibly different from gazelles. 

Unravelling the History of Seals

Allodesmus, a desmatophocid

Trying to determine the largest patterns in evolution can be a daunting task. Here, we often want to look at large numbers of species, comparing the living ones and filling in the gaps with fossils that are often incomplete, ambiguous, or that simply haven't been discovered yet. As a result, there are several big transitions in mammalian evolutionary history that we'd like to get a better look at. Bats are a significant case in point; their small fragile skeletons don't preserve well if we want to see more than teeth, and how they developed their forelimbs into wings remains obscure.

With some groups, however, we do have sufficient fossil evidence that we can look at a whole group of animals and get some idea, not just of how it originated, or where it fits in the larger mammalian family tree, but what ups and downs it has faced over the course of its existence. This can tell us what alterations in climate or geography drove changes within the group and how and when particularly evolutionary innovations developed.

Mice at the Oak Tree Cafe

Forests, it should come as no surprise, rely on a complex set of interdependencies among the native species. The animals that live in the forests rely on the existence of the trees for shelter or food, or feed on other animals that rely on the trees for food. But the trees also need the animals, or at least some of them.

Obvious examples include the reliance of many plants on insects and other animals for pollination. Another is the fact that plants have edible fruit specifically so that animals will eat them and spread the digestion-resistant seeds in their dung. That doesn't work where the animal obtains nutrition from the seed itself, as is typically the case, for example, of plants that produce nuts. But, even here, the plants may rely on scatter-hoarding.

That is to say, many seed-eating animals in temperate regions store food in caches hidden across the landscape - squirrels being among the better-known examples. Some of those caches won't be found again, or the animal that made them will die from other causes before it has the chance to use them. And then, the seeds can germinate - the great majority won't, but it happens often enough that this simple process is of key importance to the survival and growth of some nut-bearing trees.

Scratching the Surface

The environment of the Earth is shaped, not just by sunlight, wind, and the geography of mountains and seas, but by the living organisms living on it. This process has been described as "ecosystem engineering", and it inevitably affects far more than the organism that's doing the modification - sometimes negatively, but often in ways that are generally beneficial.

In its broadest sense, ecosystem engineering can include changes to a habitat caused by the mere existence of an organism. The existence of multiple trees in close proximity creates a forest, which is a very different sort of environment to, say, a grassland, and this obviously has huge effects on what the resulting habitat is like for other organisms. One could also think here of coral reefs or the nutrient-rich hotspots created by a whale carcass sinking into the depths.

Antilopine Antelopes: Almost-Gazelles of Tibet

Tibetan gazelle

It's often the case that the common name of a type of animal in English does not map directly to a scientific understanding, especially once we add modern genetic discoveries into the mix. So it is with the word "gazelle", which derives from an Arabic word that literally means something like "graceful" or "slender" and is used to refer to a range of relatively slim, fast-running antelopes. 

In a stricter, scientific sense, gazelles would really only include those species closely related to the genus Gazella, short-coated animals, often with dark stripes down the side, and that tend to live in hot deserts or semidesert regions. Even this excludes animals such as springboks, since they are less related to the true gazelles than is, say, the blackbuck. Most true gazelles live in Africa, but there are some in Asia, mostly in the Middle East, but with one reaching as far east as northern China. However, a second group of animals commonly called "gazelles" also lives in Asia, and not somewhere that most Westerners would generally associate with such animals.

Oligocene (Pt 10): The First Elephants with Trunks

Barytherium

During the Oligocene, Africa remained an island continent, separated from Asia by the Tethys Sea that ran from the Atlantic, through what is now the Mediterranean, and then south of the Zagros Mountains to connect with today's Persian Gulf. The Tethys was narrower in the Oligocene than it had been in the preceding epoch, due both to Africa's slow northward movement and the fact that sea levels were lower, but it was still substantial. As a result, the large herbivores of Eurasia, such as pigs and rhinos, had yet to enter Africa, resulting in quite a different fauna there.

The same was not, however, necessarily true of smaller mammals, some of which had been there for some time, more able, perhaps, to be accidentally carried across on floating vegetation. (A rare event, to be sure, but tens of millions of years gives a lot of opportunities to get it right). There may not have been antelopes in Africa yet, but there were certainly rodents.

Drought and the Mother Rhino

You may be surprised to discover that the white rhinoceros (Ceratotherium simum) is not internationally listed as an endangered species. This is because it is reasonably widespread across southern Africa, poaching of the species has been in decline since 2014, largely due to effective enforcement methods. While it did almost go extinct in the late 19th century, well over 10,000 of the animals are thought to be alive today, with populations in some areas still rising in recent decades. In fact, it meets all the usual criteria for a species of "least concern", one that we wouldn't normally consider even close to being threatened.

This, of course, hides a fair bit of complexity.

Antilopine Antelopes: The Giraffe-Gazelles

Gerenuk

Despite appearances, true gazelles are not the closest living relatives of the springbok. That honour is probably tied between two other species, although there have yet to be sufficient genetic studies to absolutely nail that down - one could be closer than the other. They likely diverged from the springbok over 10 million years ago in the late Miocene, earlier than the blackbuck is thought to have diverged from the true gazelles, so it's perhaps unsurprising that they look quite different.

They also look slightly odd, and very distinctive.

The better-known of the two is the gerenuk (Litocranius walleri). The name comes from the Somali word for the animal, but it is more commonly known as the "giraffe-gazelle" in many European languages, and it's easy to see why. It is, of course, much smaller than a giraffe, with males having a shoulder height of around 100 cm (39 inches). The colour is also different, a relatively uniform reddish-brown over the back, with a paler shade in the flanks, neck, and limbs, and stark white underparts. There are also white markings on the face, around the eyes. Only the male has horns, which rise almost vertically out of the skull before curving back in an S-shape.

Giant Kangaroos: Were They Utterly Hop-less?

Most people have a clear image of what a kangaroo is: a large herbivorous animal that carries its young in a pouch and that moves by hopping about on its hind legs. There are three living species of true kangaroo, and this description does, indeed, accurately fit all of them. However, the kangaroo family, or Macropodidae, is much larger than this, with a total of 63 species, most of which can generically be described as "wallabies". 

There are also several fossil species known, stretching back to the late Oligocene, over 25 million years ago. Having only skeletal remains, and often partial ones at that, while we know that they had sufficient similarities to be placed in the same family and their teeth indicate they were herbivorous, what about the other two features: pouches and hopping? 

Cubs in the Snow

Both brown and American black bears spend much of the winter asleep. Whether this counts as true 'hibernation' is debatable, although, in recent years, most scientists no longer insist on a strict physiological definition, having given in and accepted the word as it is usually understood in English. They do this because their food is in short supply during the winter, and spending the entire time snoozing is a good way of conserving energy.

Before hibernating, they construct a den, in which they will spend the next several months, depending on the exact weather conditions. Significantly, mothers of both species give birth in the den, often while they are still asleep. All of which works for a large, omnivorous animal living somewhere that inclement weather makes it hard to forage in winter. But that's not something that will be true of all bears.

Bats in the Daytime

One of the things that we can say about almost all species of bat is that they are nocturnal. Regardless of whether they roost in caves or under the branches of trees, bats sleep through the day, wake up around dusk, fly out to get their food, and return home when the sun rises. But, when you stop to think about it, why should that be?

Consider: the great majority of bats eat insects and, sure there are plenty of insects around at night. But there's hardly a shortage during the day, either. Swallows, robins, and thrushes are all flying vertebrates that eat insects, and you see plenty of those around during the day. While for fruit bats and other herbivorous species, it's quite obviously not going to make a difference. If birds are perfectly happy flying around during the day, why not bats? It's not even as if there are only a small number of bat species that happen to occupy some narrow niche; there are well over a thousand of them.

Antilopine Antelopes: Blackbuck and Springbok

Blackbuck

The gazelle-like body form has evolved at least three times within the "antilopine" subfamily, and arguably a few more times among antelopes more generally. A fast-running animal, able to outpace many of its predators, is clearly a useful thing to be if you're a herbivore. Only one of these three evolutionary events led to what zoologists would describe as the "true gazelles", although at least one of the others resulted in an animal so strikingly similar to gazelles that it's surprising that molecular evidence tells us it doesn't have an immediate common ancestor.

The blackbuck (Antilope cervicapra), however, does not look much like a gazelle. It is one of the five currently recognised species of antelope whose scientific name dates back to the origins of modern taxonomy in 1758. In 1766, Peter Simon Pallas first distinguished antelopes from goats, creating the genus Antilope to incorporate no fewer than seventeen species - including the Dorcas gazelle, which would later go on to become the defining species of the Gazella genus when that was created in 1816. While every other living species was eventually split off elsewhere, the blackbuck remained, and its genus gives its name to the entire subfamily. (The second part of the name, incidentally, translates as "deer-goat" and remains the name of the animal in French).

Oligocene (Pt 9): Rise of the Dogs

Sunkahetanka

Many of the carnivorous mammals present in North America during the Oligocene were of types also found in Eurasia. However, this far back in time, they did not necessarily belong to any family of animals we would recognise. Cats, for example, first appeared in Europe at the end of the epoch and did not reach the Americas until much later. Other groups, such as raccoons, simply didn't exist yet. 

But we do, for example, have Palaeogale, an animal also known from Europe that looked somewhat like a polecat, but was actually more closely related to cats and mongooses without, so far as we can tell, being either. Corumictis looked similar, but analysis of the skull has shown that it much closer to true mustelids. About the size of a modern weasel, it lived in Oregon at least 29 million years ago, towards the middle of the epoch. It may make it the first mustelid to reach North America from Eurasia, home to the very similar, and slightly older, Plesictis. It's far enough back that it might, however, belong to an early musteloid group rather than to the modern family (that is to say, it may be equally related to mustelids and raccoons, and thus, strictly speaking, neither). Oaxacagale is almost as old, and lived in what is now Mexico; it's probably another close relative but, it too, has so many primitive features that it's hard to place precisely.

Wombats Moving Home

There comes a time in the life of many young mammals when they have to leave home. There are at least two major reasons for this. Firstly, any given place only has so many resources, so unless your parents die as soon as they've finished raising you (unusual among mammals, although not unheard of), at some point, you have to move elsewhere or there won't be enough food for both of you. Secondly, if the whole family stays together in one place, you'll never meet new sexual partners, forcing you to mate with your siblings - and we all know where that leads.

Understanding how and when animals disperse from their place of birth can be important for conservation as well as, on a broader scale, how new species and subspecies evolve and adapt. Nor is it necessarily something that only applies to young approaching maturity, since older animals may also choose to move from one place to another and often for similar reasons - competition or a lack of suitable mates. Whether a given animal chooses to move home, and how far they travel to do so, can be influenced by several different factors. 

The Vocabulary of Sperm Whales

It's well known that whales and dolphins can communicate using sound, sometimes over long distances. In some cases, this can involve sophisticated "whalesong" that animals can use, for example, to identify each other, and that may impart other information, too. But there are a great many species of cetacean, and what is true for one won't necessarily be true for all of the others, just as what's true of chimps won't always be true for baboons or marmosets.

We'd expect the most complex messages to come from those species with the most complex social lives. In these cases, it would be useful for the animal to identify not only its gender, fitness, sexual status, and so on, but also which other whales it might associate with, and where it stands in the local hierarchy. Most (but not all) cetaceans live in pods although, for many, we haven't gotten very far in identifying how those are structured. They all, however, have relatively large brains and it can be worth asking, for any given species, just how complex their communication really is.

Antilopine Antelopes: The Largest Gazelles

Grant's gazelle

The word "gazelle", as used in everyday English is a little vague, referring to a general concept of slim, agile, antelopes but not to anything with a precise scientific definition. Strictly speaking, however, it refers to a specific group of closely related animals, and some species that are commonly called "gazelles" strictly speaking aren't. During the 20th century, all true gazelles were placed in a single genus, Gazella, and it's this that defines the more rigid definition of what does and doesn't count. 

In more recent decades, Gazella has been split in three, with the resurrection of two 19th-century names as "new" genera. The original Gazella is widespread, including animals from both Asia and North Africa, but the other two are exclusively African. Eudorcas (literally "true antelope" in Ancient Greek) includes Thomson's gazelle of the Serengeti and its various relatives, while the remaining genus is Nanger, whose name apparently comes from a local Senegalese word for one of the species.

Before Cats Could Purr

Hyperailurictis

Although the differences are obvious when we can see the spots or stripes on their fur, the various species of cat are often very similar in form, and it can be hard to tell them apart based on the skeleton alone. For this reason, through much of the 20th century, all of the "purring cats" except the cheetah were placed in the single genus Felis. That's not the case today, when we distinguish genera not only for the larger purring cats, such as pumas and lynxes, but others that modern genetic evidence tells us are distinct, such as the group that includes the ocelot.

Given this, it's hardly surprising that the same should go for fossil species, too. It may well be that if we had genetic evidence on those, or could even just see their coat colour, we would be more willing to distinguish them but, when all you have is an often fragmentary skeleton, there isn't much to go on.

Squirrels, Advance!

The rapid growth of human population over the last century or so has led to a decline in many species. As I talked about last month, however, some animals can live alongside us even in urban environments, and there are many more than can tolerate us in rural - yet not truly wild - habitats, such as cropland or pasture. Any species that can do this clearly has an advantage, in many cases being able to move into new parts of the world previously inhabited by some similar, but less human-tolerant species. Thus, we can see some native species replaced by foreign invaders, as has happened, for example, with mink in continental Europe and jackrabbits in the American southwest.

In Britain, the most familiar example of this is probably the replacement of our native red squirrels (Sciurus vulgaris) by invasive eastern grey squirrels (Sciurus carolinensis). Red squirrels were once common across the British Isles, but have now vanished from most of England and Wales, surviving in the far north of England and a few pockets elsewhere, but otherwise replaced by the greys. In large part this is due to the greys carrying a virus to which they are immune but the reds are not, but simple competition is another factor.

Call of the Elephants

Arguably the single most significant feature that has enabled our own species to dominate the Earth is our possession of language. This enables us to communicate and cooperate to achieve things we could not do individually, to an extent unparalleled outside of social insects, which lack our ability for complex thought in other ways. Without language, it's hard to see how we would have built cities, or maintained the incremental advance in knowledge that has marked many thousands of years of our history.

Yet language, of course, did not arise from nowhere. There is an understandable interest among scientists in determining how it might have evolved, and what from. Since we can't go back in time to perform linguistic analysis on the likes of Homo erectus, one of our major sources of information is determining how other species of mammals communicate using sound, rather than the scent marks that are so important to many of them. Much of the focus here is on primates, since these are the most likely to hold clues to our own origins, but this can be extended to other species, too. To what extent do other animals have something that could be considered ancestral to language?

Antilopine Antelopes: The Gazelles of Asia

Arabian gazelles

I suspect that, on the whole, westerners associate gazelles with Africa. We think of the ones we see in wildlife documentaries, being pursued by cheetahs or leopards across the plains of the Serengeti or similar places. However, the most current theory suggests that they may have originated in Asia and various species survive on both continents today, having split apart around 2 or 3 million years ago at or shortly before, the start of the Ice Ages.

How many species that might be is still a matter of debate, and much of it centres on what's probably the first part of Asia you'd think of to look for desert-dwelling animals: the Middle East. For much of the 20th century, there were generally regarded as being two species living here, not counting one or two then thought to be extinct. And then, well, all that fell apart for reasons I wrote about on this blog back in 2013.

Oligocene (Pt 8): The First Tapir and the Last Hoofless Horse

Miohippus

A close look at the evolutionary history of horses reveals that it's more complicated than sometimes presented, with numerous side branches forming a bushy tree of different species, many of which ultimately died out without descendants. This applies both to the origins of the group in its early days and its period of great diversification through the Miocene and Pliocene epochs. In the Oligocene, however, the picture, at least so far as we can tell, was rather simpler.

We know of two genera of horse that made it into the Oligocene from the preceding epoch. Mesohippus had been around for a while, Miohippus was a relative newcomer, appearing towards the very end of the Eocene. The two are rather similar, to the point that it has been argued they should be treated as different species of the same genus (which would be Miohippus, as that was named first) and they are both found in fossil beds across the United States and southern Canada, with Miohippus being known from Washington state to Florida and Mesohippus primarily in the west. The similarity also led to proposals early on that the one directly evolved into the other, but it's now clear that they lived alongside one another for millions of years, which scuppers that idea.

Wild Mammals of London

Arguably the single biggest threat to the continued survival of animal and plant species is loss of habitat. Even if an animal isn't actively hunted, the ever-growing human population means that there are simply fewer suitable places for them to live. Logging and the expansion of agriculture are probably the biggest factors here, at least in terms of the area affected, but it's hard to argue that the recent growth of urban sprawl isn't another.

The urban environment is obviously a difficult or impossible one for most wild mammals to exploit. House mice and rats are an obvious exception, and there are also domesticated pets, but for truly wild creatures it's a different matter. While it may no longer have (say) bison or wolves, upstate New York is still home to seven species of shrew, three moles, four hares or rabbits, 22 different kinds of rodent, ten bats, nine mustelids, two foxes, and three deer, plus coyotes, bobcats, raccoons, striped skunks, and black bears. Manhattan... not so much.

Flight of the Fossil Pelicans

Dalmatian pelican

Pelicans are distinctive birds with long necks, short legs, and a remarkably long beak the bottom half of which is attached to a large extensible pouch for holding captured fish. They are also large, with even the smallest species having a 180 cm (6 foot) wingspan and the largest being half that again. They are, of course, water birds, with many living along coasts or in brackish waters, but others found in lakes and rivers far inland.

They are also not mammals, which is a timely reminder that, yes, this is the post that will be live on 1st April, when I switch things about for one post a year.

Antilopine Antelopes: Gazelles of North Africa

Dorcas gazelle

(Brief note: My internet connection was down for three days over the weekend, which is why this post is delayed from the usual.)

One of the things that most distinguishes gazelles from other kinds of antelope is that they are adapted to dry environments. They don't come much drier than the Sahara so it should be little surprise that gazelles are relatively common here. In fact, the dorcas gazelle (Gazella dorcas) is one of the most widespread of all gazelle species, being found right across the Sahara from the Atlantic to the Red Sea, as well as further south along the Red Sea coast in Eritrea and Djibouti and across the Sinai into extreme southern Israel. In the north, it's largely restricted to the eastern parts of the Mediterranean coast, being absent from northern Algeria, Morocco, and Tunisia.

Home-grown Shovel Tuskers?

Konobeladon

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.

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 proboscideans. 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".

Jiggling on the Ecotone

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.

In many species, this takes the form, not of solitary deposits, but of latrines. 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 significant clues about what those messages might be.

The Rhinos of Samos

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. 

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. 

Antilopine Antelopes: Tommy's Gazelle and Relatives

Thomson's gazelle

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.

Gazelles are smallish, fleet-footed animals; the word comes from the Arabic ḡhazāl, 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 Thomson's gazelle (Eudorcas thomsonii) 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.

Oligocene (Pt 7): Not Quite Camels, Not Quite Pigs

Protoceras

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. Protoceratids 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 Protoceras, known primarily from Nebraska, Wyoming, and South Dakota.

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, Protoceras 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. 

A Tiger's Dinner

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.

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 does mainly eat smaller carnivores). Outside the world of mammals, one could add eagles, crocodiles, and sharks, among others. Humans could count as another example, given that we obviously don't have regular predators, but this does depend on your exact definition, since we're clearly omnivorous and, in many parts of the world have a nearly or totally herbivorous diet.

Playing Squirrels

Anyone who has owned a cat or dog will know that playing with toys is not something unique to our own species. Indeed, playing in general is a widespread phenomenon among mammals, and less commonly, in other animals, too. (Crocodiles and alligators, 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.

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 2005 book on the subject, which defines play as a physical activity meeting four key criteria.

No Such Thing as an Antelope

There is no such thing as an antelope.

Or at least that's true in the same sense that there's "no such thing as a fish". 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.

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.

Rise of the One-Toed Horses

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: Equus.

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.

Boys or Girls?

Generally speaking, a newborn mammal is equally likely to be male or female. The sex ratio 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 wasn't the first to have thought of it).

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. 

The Rarity of Gophers

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.

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"?