Q&A 2012

This is a synapsid, and not a reptile. Yes, really.

This will be the last post at Synapsida before the New Year, so I thought I'd do something a little different this time. A lot of the hits on this blog are from Google searches, with a few from similar services like Bing. Often, the searches that bring people here are questions, and the blogger.com interface lets me see what those questions were. I don't check it religiously, so I'm sure there must be many questions that brought people here that I've never seen. But, just for fun, this week I'm going to answer some of the ones I have seen.

It's not going to help the people who asked the questions in the first place, of course. And, if anyone asks the question again, there's no guarantee they'll be directed to this page, rather than wherever they were directed before. But what the heck - why not, right?

So without more ado:

Is [X] a Synapsid?

This seems to be among the top two or three questions that bring people to the site. Is a cow a synapsid? Is a tiger a synapsid? What about a monkey? Or a kangaroo? And so on.

Mazes and Mole-Rats

The African mole-rats are a family of bizarre rodents, and one that I've discussed before. Their most famous member is the exceptionally weird naked mole rat, but the other, furrier, species are still pretty odd. They spend almost their entire lives underground, feeding on plant roots, and, as a consequence, are virtually blind. Famously, naked mole rats are 'eusocial' mammals, living in the style of ants or bees, with a single breeding queen and a number of sterile workers. However, some other African mole-rats live solitary lives, and others, while not as extreme as the naked species, are still strongly social.

We know very little about some of the species, but others have, on account of their peculiarity among mammals, been well studied. One of these is the Zambian mole-rat (Fukomys anselli). Much of the work on this species has concerned their hearing abilities. They turn our to be particularly good at hearing low-pitched sounds; the sort of noise that rumbles through the soil, and echoes through their narrow tunnels. Not only that, but they are also able to detect magnetic field lines, presumably to orient themselves in the absence of any cues from the sun.

How do Dolphins Sleep?

All mammals need to sleep. Quite why isn't entirely clear, although it may well have to do with saving energy, allowing the body to repair itself, consolidating the memories of experiences learned during the day, or any of a number of other reasons. What is clear is that it's very important, and that there's no way to avoid it in the long term. Indeed, it's not just mammals that do it, but also all species of bird, and probably just about every other creature with a brain, whether vertebrate or invertebrate. (Creatures without a brain, such as jellyfish, don't seem to sleep, although, to be honest, it's hard to see how you could tell if they did).

But sleep presents a problem, in that the animal is vulnerable while it's snoozing. This is why most mammals make dens of some kind to which they can retreat overnight - or during the day, if that's their preference. Dens, of course, can be remarkably varied, whether they are carefully constructed burrows, crevices in tree trunks, natural caves, or whatever, but most animals that live in the right sort of environment have them.

Weasels in Stone: Mustelid Evolution

Sthenictis, a fossil mustelid

Last September, I began a survey of the weasel family, the largest, and arguably the most varied, family of carnivorous mammals. Since then, I have managed to give at least a brief description of every living species in the family, from stoats and badgers to otters and wolverines. But how do all these animals relate to one another, and where did they come from?

In the past, scientists would work this out by examining the physical features of animals, reasoning that those with the greatest similarity were the most likely to be related. By adding in information gleaned from fossils. such as their age and location, and any evolutionary changes they may have undergone, it's possible to get quite a lot of information this way. However, today, it is more common to use molecular and genetic information, seeing how genes and the proteins they produce have changed in subtle, often invisible ways, over the course of time. Taken together with the fossil information, this can reveal many relationships that might otherwise remain obscure.

In the very first attempt at scientific classification of animals, way back in 1735, weasels were grouped together with martens, polecats, and civets as a sort of collective group of small slender mammalian carnivores, although otters and badgers were placed separately.  However, it was not until 1817 that the weasel family was formally named by German naturalist Johann Gotthelf Fischer von Waldeheim. That, of course, was still before we understood evolution, and it's hardly surprising that we've moved on since then.

News in Brief #7

Geoffroy's spider monkey

Monkey Sleep, Monkey Poo

Poo is useful stuff to zoologists: a lot of field work involves examining the stuff. It can tell you what an animal has been eating, how it behaves, and maybe something about it's genetics. And, of course, it can also tell you where it's been. Take Geoffroy's spider monkey (Ateles geoffroyi), for example.

Spider monkeys are moderately sized monkeys, noted for their prehensile tails and remarkable agility. I saw some (although not Geoffroy's species) at London Zoo on Monday, and, despite the poor weather, they really were a delight to watch, full of enthusiasm and energy. Seeing them at play, it's hard to escape the impression that they have five arms: their feet are effectively an extra pair of hands, and their tail is so flexible and has such a good grip that it might as well be a fifth one.

They live, unsurprisingly enough, up in the trees - specifically ones in Central America - sleeping in them at night and travelling between them to feed during the day. They have particular favoured trees to sleep in, and deposit a lot of dung at the base over the course of the night. Such 'latrine' use is common among many mammals, and just finding where they are provides a good means of establishing what the monkeys are up to without having to disturb them.

Pleistocene (Pt 5): Giant Deer and Woolly Rhinos

There were a number of Ice Ages during the Pleistocene, but the most severe of them all seems to have been the most recent one - the Last Ice Age. Or, perhaps more accurately, the Last Ice Age So Far, since there's no particular reason to assume there won't be another one along in a few thousand years time. This was the time when the earlier steppe mammoths were replaced by their more famous descendants, the woolly mammoths. But woolly mammoths did not live in isolation. With what other creatures did they share their world?

Even today, deer are relatively common animals in the wilder forests of Europe. In the Pleistocene, before the spread of farms and towns, they would have been even more so. At the height of the last Ice Age, however, there were relatively few forests in Europe, and many of the deer we are familiar with - red deer, roe deer, and so on - would have been sheltering in warmer climes. Reindeer and moose, on the other hand, were doing well, with the former, in particular, being widespread across the continent.

Throughout the course of the Pleistocene, however, there had been another kind of deer in Europe, one that is no longer with us. These were the "giant deer" of the genus Megaloceros. Some species, isolated on islands created by the rising melt-waters of the glaciers between the Ice Ages, were unusually small, but, in general, they had been getting larger as the Pleistocene went on. Before the last Ice
Age, the largest species, slightly bigger than the primitive moose of the day, had been M. verticornis. Now that was replaced by an even larger species, the Irish elk (Megaloceros giganteus).

It's Tough Being a Herbivore

A horse skull

The majority of mammalian species are, to a greater or lesser degree, herbivorous. This shouldn't be too surprising: there is always more plant matter around than there is fresh meat, and it's a lot easier to catch. While the earliest mammals may well have fed on things like insects, a great many have since taken advantage of the widespread presence of plants to become herbivores.

Strictly speaking, most won't absolutely refuse to eat animal matter. For one thing, if you're munching down on leaves, you're going to eat the odd insect now and then, if only by accident. And most mammalian herbivores will, in reality, eat the occasional bit of - mostly invertebrate - flesh, or tuck into things like eggs if they find them lying around. But these are a minor part of their diet at best, allowing us to draw a useful, if hazy, line between them and true omnivores.

The largest order of mammals are the rodents. While many are genuinely omnivorous, most use their great gnawing teeth to feed on things like nuts and hard seeds. This illustrates one of the problems with herbivory: while your food might be easy to catch, it's not necessarily very easy to eat. Many wild plants are hard or thorny, and they're often not as packed with nutrients as meat is. As a result, herbivores usually spend a lot of their time feeding, and they require special adaptations to make the most of their meals.

How Deep is a Prairie Dog's Burrow?

The Utah prairie dog has the biggest burrows

If you live in Britain, or, for that matter, many other parts of Europe, a "squirrel" is a bushy-tailed rodent that lives up trees. But this is by no means an adequate description for all squirrels. A great many squirrels are ground-dwelling animals, and would rarely, if ever, climb a tree. This is even more apparent when we look at the squirrel family as a whole: there are something like three hundred different species of squirrel worldwide, and only around half of them live in trees. The others generally dig burrows.

Squirrel burrows include a deep nest chamber, in which the animal can sleep, rear its young, or simply hide from predators. Connected to this there will usually be a number of tunnels, and multiple entrances. In the event that, say, a weasel, chases you into your burrow, it is really important to have an escape route, so a single entrance is unlikely to be enough.

Considering that squirrels are relatively small animals, these tunnel systems can be quite impressive. Since they're only using the burrows for shelter, they won't necessarily be as dramatic as those of animals like moles, that also need them to travel in search of food, but they can still be quite long and deep.

How long, and how deep? Well, that depends on a lot of factors. Different species will dig different kinds of burrow, and there's no reason to assume that, even given identical circumstances, all members of the same species will dig identical burrows. In any event, circumstances aren't identical. The nature of the environment, and particularly the soil, will affect how big a burrow it's practical to dig at all, even assuming you wanted to - and, generally speaking, animals won't dig a burrow any bigger than they have to, because it's exhausting work.

Weasels of Mystery: the Ferret-Badgers

Chinese ferret-badger

So far, in my survey of the weasel family, I have covered a number of familiar species: stoats, badgers, and otters, among many others. There have also been a few species probably less familiar to those of us in the west, such as zorillas, grisons, and tayras. But the least studied of all belong to the last subfamily I have to cover: the ferret-badgers.

Ferret-badgers are, of course, neither ferrets nor badgers, but entirely their own group. As the English name implies, they have features some way between the two animals for which they are named, although they are distinct in a number of ways, too. Their total body length is not far off that of a ferret, but they have the stocky build of a badger, and so somewhat resemble a smaller, slimmer, version of that animal. Proportionally, though, their tail is longer than that of a badger, and they have a narrower, more pointed snout. They have greyish or brownish fur over most of the body, which, again, looks quite badger-like, and black-and-white markings on the face.

However, these markings are not the clear stripes of a badger, although they aren't really the 'mask' pattern found on ferrets, either. One distinctive feature of the markings is a white stripe running from the forehead down over at least the neck, and often further down the middle of the back. American badgers have something similar, but it's often more striking in the ferret-badgers. Like many other members of the weasel family, the creatures are said to have a strong odour, and they're also quite fierce, so it could be that the highly visible markings serve as a warning to other animals.

Life of an Almost-Mammal

Scaloposaurus, a therocephalian.
This artist has chosen to show it hairy, which is plausible,
but uncertain.

When I was at school, I was taught that mammals evolved from reptiles. However, at least under the modern definition of 'reptile', that isn't really true. In fact, the mammals belong to their own, distinct, evolutionary lineage, one that has existed alongside the reptiles ever since the latter first came into being. This is a staggeringly long period of time - by definition, it's from long before there were any dinosaurs, for example.

However, this evolutionary group didn't just include the mammals themselves. Mammals may not have evolved from reptiles, but they haven't been around anything like as long in the fossil record. So, if we look back to before the first mammals evolved, we find that there were many other kinds of creature belonging to this group that are no longer around today. Because evolution isn't really a ladder, some of these animals survived alongside the early mammals. In fact, the last ones didn't die out until well after the split between placentals and marsupials.

Studying fossils of these creatures can tell us a lot about where mammals came from, and how they became so different from the reptiles.

Why are Elephants Hairy?

The Asian elephant is the hairiest of the three living species

Elephants are, as is well-known, the largest land-dwelling animals alive today. Being so large presents a number of problems, and these are only increased by the fact that elephants, being mammals, are warm-blooded. Specifically, they have to maintain a body temperature of 36°c, only one degree below that of humans.

Perhaps the most obvious problem is that they need to eat a lot in order to survive. The need to keep their metabolism going means that they need more calories for their size, than, say a crocodile, which - being "cold-blooded" - can rely on the sun to warm it up. However, that internal body heat presents another problem as well, and that's keeping cool.

The larger an object is, the smaller its surface area proportional to its volume. This is basic mathematics; if I double the dimensions of an object, while keeping it the same shape, the surface area increases four-fold (2²), but the volume increases eight-fold (2³). Since heat is lost through the surface, the bigger an animal is the more heat it will tend to retain. This is actually a greater problem for small animals than large ones, since they tend to lose heat rapidly, and therefore need a very high metabolism just to keep up. Mice, shrews, and the like need to eat a huge amount, relative to their size, in order to keep functioning. It obviously doesn't help if the weather is cold, which was the original reason proposed for Bergmann's Rule - the idea that animals are larger in cold climates than they are in warm ones.

Pleistocene (Pt 4): Time of the Woolly Mammoths

The second-to-last Ice Age ended around 0.13 million years ago, a full 95% of the way through the Pleistocene. As I've described in Part 3, it was just one of a series of Ice Ages stretching back nearly two million years, and separated by relatively warm 'interglacials'. For much of this time, European wildlife had had a distinctly 'African' flavour, with lions, hyenas, hippos, and elephants, among others, inhabiting the continent alongside the ancestors of more familiar European animals.

Such animals prospered during the warmer gaps between the Ice Ages, and this, the last full interglacial, was no exception. The phrase 'hippos in the Thames' is often used when talking about this time, and its perfectly accurate. The climate of the day was, if anything, slightly warmer than it is now, with the ice retreating far into the Arctic. All that melting ice had to go somewhere, of course, and the sites of modern day coastal cities such as Amsterdam and Copenhagen would have been underwater. On land, much of the northern continent was covered by dense oak forests, a green wilderness yet to be cleared to make way for farmland or towns.

Weasels on the Savannah: Zorillas and their kin

Saharan striped polecat

Even before we had good molecular and genetic evidence for how the various members of the weasel family were related to each other, there were a number of different schemes proposed for dividing up the family into smaller groups. Otters were almost universally agreed to be something different from the other weasels, and, in the simplest scheme, everything that wasn't an otter was considered a "musteline". Once the genetic information arrived, it wasn't a terribly great surprise to learn that the martens were a group, the 'true' badgers were a group, and so on. Removing badgers, martens, and the like, meant that the term 'musteline' now referred only to the weasels themselves, and their closest relatives: stoats, polecats, and mink.

What was rather more surprising though, was that one group of what seemed to be quite clearly weasel-like animals actually constituted an entirely separate branch of the family tree. Mostly living in the southern hemisphere, it had not really been obvious before that these animals were especially closely related to one another. Because of that, unlike badgers, otters, and martens, they had no collective name in English. The scientific term for members of this group is "galictines", and that remains the best word we have for them.

News in Brief #6

Japanese macaques

Baby Monkeys are Cute

For we humans, it's fairly easy to estimate how old another human is just by looking at them. It may not work perfectly, but we can instinctively assign someone to at least to a broad age class - young adult, middle-aged, and so on. There are plenty of clues to help us to do this, and it's a useful ability for shaping our interactions with one another, so it's not too surprising that other social animals can do the same thing. Perhaps one of the more striking examples is our reaction to the faces of our young.

Very young humans have a constellation of features that highlight their age: rounded face, large eyes in comparison to the face, and so on. The same set of features are found in other baby mammals, and were described by the great behavioural biologist Konrad Lorenz as "kindenschema". Perhaps a more everyday term for the same phenomenon is "cuteness". Cuteness triggers positive, maternal and protective reactions in humans, and its by no means restricted to our own species. Kittens and puppy dogs are undeniably also "cute" to the vast majority of humans and its for the same reasons. We can see the same phenomenon in the looks of toys such as teddy bears, the kawaii appearance of characters in Japanese cartoons, and so on.

Fossil Porpoises Muddy the Waters

Harbour porpoise

Dolphins and porpoises belong to two separate families, and there are clear differences between them. However, this isn't immediately obvious at first glance: they're both small cetaceans, with flippers, tail flukes, and so on. A comparison between, say, a bottlenose dolphin (Tursiops truncatus) and a harbour porpoise (Phocoena phocoena) does show a number of differences that are broadly true of their respective relatives - but not entirely so.

Porpoises, for instance, are smaller than dolphins, on average. But only 'on average', because, in fact, the smallest dolphin is smaller than the smallest porpoise. Similarly, dolphins usually have a 'beak' - a narrow snout projecting forward from the front of the head - that is missing in the more rounded heads of porpoises. But, once again, there are dolphins that don't have the beak, such as Risso's dolphin (Grampus griseus).

Discovery of the World's Newest Monkey

Hamlyn's monkey (left) and lesula (right)

Even today, new species of mammal are being discovered all the time. The majority are small animals, often nocturnal, or otherwise difficult to find. Just in the last few months I've seen the announcement of four new bats and a mole, and that's without me particularly trying - there may well be more discoveries I haven't seen. In many cases - as happened with the bats, for example - it's not that the animal had never been seen before, it's just that it wasn't obviously a different species. Until you look closely, one mole may look much like another.

The discovery of larger species is a rarer event. Which is why the announcement of an entirely new species of monkey is so exciting. This new animal, the lesula (Cercopithecus lomamiensis), is the first new species of African monkey to be discovered since the critically endangered kipunji in 2004, and only the second since 1984.

How Armadillos Get Their Armour

Screaming hairy armadillo

Reptiles are scaly, and mammals are furry. That's a broad general rule, and holds in most cases. But there are, of course, a number of exceptions. Many mammals, such as dolphins and hippos, are not at all furry, for example. And, while there are no hairy reptiles, there are two groups of mammals that have scales.

One of these, the pangolins, have scales that are quite unlike those of reptiles, giving them a unique appearance. The other is the armadillo family, and, in their case, the scales really are quite reptile-like. It's a form of parallel evolution, where two or more groups of animal independently evolve the same solution to a particular problem. The ancestors of armadillos would have been as hairy as any other mammal, but when they evolved protective armour, they ended up with something that is quite similar to the scaly plates of, for example, crocodiles.

Weasels Digging Holes: American and Honey Badgers

American badger

It was thought at one time that the various species of badger were fairly close relatives within the weasel family. More recent genetic evidence has shown us that that's not the case, and that there is more to their story than one might guess from simply looking at them. While the majority of badgers do indeed belong to a single, related, group - what we might call the "true" badgers - there are some exceptions.

In fact, the badger body plan and lifestyle appear to have evolved at least three times within the weasel family. One instance led to the "true" badgers, with at least four species, and possibly more not yet formally recognised. The other two are no more closely related to the "true" badgers, or even each other, than they are to, say, otters or stoats. In each case, only one member of the lineage survives today, giving us two "subfamilies" with just one living species each.

Of the two, the better known is surely the American badger (Taxidea taxus). Despite being as genetically distant from the European badger as its possible to be without belonging to an entirely different family, it's really not hard to see why early American colonists chose to give it the same name as the animal they were already familiar with. In addition to the short limbs typical of all members of the weasel family, it has a compact, muscular body, wedge-shaped head, and powerful digging claws. That's not really so surprising, when you consider that there are only so many ways to modify the body of a weasel to make it into an effective digger.

Pleistocene (Pt 3): Ice Ages and Interglacials

Life-size reconstruction of a steppe mammoth
(compared with a 3-year old human)

When the Pleistocene began, Europe's climate was much the same as it is today, and the general shape of the continent would also have been instantly recognisable from space. The animals however, were different, many of them being ones we would now associate with Africa - rhinos, elephants, hyenas, and cheetahs, among others. In part 2, I described how that began to change 1.8 million years ago (which, incidentally, was once defined as the beginning of the Pleistocene - see part 1 for why that changed).

This was a time of cooler weather, as the Ice Ages began to dawn. Forests retreated in the face of advancing tundra, and musk oxen, bison, and (strangely) European hippos began to make their appearance. The cold snap was prolonged, and, so far as we can tell, the fauna of Europe remained relatively stable for the next 600,000 years. That's still a very long time - if we go back to my analogy where we get just one minute to watch the events of a decade, with the whole of written history thereby spread out into a nine hour spectacular, this phase of European history would last a full six weeks.

1.2 million years ago, half way through the Pleistocene, the climate changed again, and mammals (and other animals) were forced to adapt. However, the change wasn't towards yet colder weather, but back towards a warmer, more pleasant climate. The forests grew back, with all their dense undergrowth in attendance, and the harsh steppe-lands retreated into the north. As had been the case at the dawn of the Pleistocene, European weather would have been much as it is now.

100th Synapsida

This is the 100th post on Synapsida. Granted, that's counting the introductory post, which didn't really say much, but it's far easier to keep track of that way. Synapsida started in October 2010, initially with around 2 or 3 hits a day, and currently tends to get around 80. Not the most successful blog in the history of the internet, then, or even of science blogging, but hardly a disaster, either.

In that time, I've covered a wide range of mammalian topics, although there's still a number I believe haven't yet had a fair shake. The subject I've written most about turns out to be reproduction, followed, more generally, by animal behaviour. These are topics there's a lot to say about, and there's plenty of research ongoing, as well as being easier to make interesting than, say, the diversity of nitrogen isotopes in reindeer. Still, I'd like to do a bit more on morphology - the general shapes and anatomy of animals, and how that differs between groups.

I've covered members of 33 different families of mammals in the main articles, and so far, I've generally not gone into detail on any given species more than once. Still, some types of mammals have definitely featured more frequently than others. Aside from the obvious, the most commonly mentioned family of mammals turns out to be the dogs, followed by the bears. In general, carnivorous mammals have got the most airtime, but there are also a number of posts on marsupials, bats, primates, and cetaceans, among others.

Mating in the Rain

Cairo spiny mouse, a related species

Humans have no defined breeding season, remaining sexually active throughout the year. This is relatively unusual among large mammal species, especially in temperate regions (although it's worth remembering that our species is originally from the tropics). That's at least partly because mating in humans also serves a social function, helping to bind individuals together. We see something very similar in bonobos, but most large mammal species do have a defined time of the year when the females come into heat, and mating begins.

The reason for this is to ensure that the young are born at an appropriate time of year, when food is most plentiful. That's particularly important in temperate regions, because there's inevitably going to be a shortage of food in the winter. However, the picture can become more blurred as we move towards the tropics, and when we look at smaller mammals.

The issue in the tropics is that there is no winter, and temperatures don't change radically throughout the year. However, due to the complex nature of climactic weather systems, even in the tropics, there is usually a rainy season and a dry season. While the jungles of Southeast Asia, for example, are never going to be as short on food in the dry season as Canada is in the depths of winter, there is still a notable difference. For example, flowers and fruit may be more available in the wet season, as may fresh growths of new plants. Even for carnivores, that's helpful, because the animals you're feeding on are plumper and more numerous when there's more tasty plants around. So, many species time their breeding so that births occur during the rainy season.

Weasels in Burrows: the 'True' Badgers

European badger

The word 'badger' has been applied to a number of species of stocky, moderately sized, members of the weasel family, that are not necessarily all closely related to one another. That's not due to any sort of carelessness with the names, because, for a long time, it was thought that they were closely related.

It's hardly an unreasonable conclusion, because they do look strikingly similar to one another, even to the extent of having similar coat markings. Modern genetic analysis, however, has shown that they are rather more different from one another than appears at first glance. Indeed, one group of 'badgers' - the stink badgers - turned out not to belong to the weasel family at all, but, instead, to the skunk family.

The stink badgers are obviously beyond the scope of this series on mustelids, but the various other species are not. The remaining badgers, however, still do not constitute a single group within the weasel family, as was once thought. That's because they don't have a single ancestor from which all other badgers - and crucially, nothing but badgers - are descended. All badgers are related, because everything is related, if only you go back far enough, but they're often more closely related to other animals than they are to each other.

Pleistocene (Pt 2): Europe at the Dawn of the Ice Ages

Pachycrocuta brevirostris, a European hyena

The Pleistocene is the time of the Ice Ages, when great ice sheets rolled across much of the northern hemisphere. Nothing much lived on the ice sheets themselves, just as there is very little today in the heart of Greenland. But, as we've seen, not only were their wide bands of tundra and pine forest reaching across much of today's 'western' world (and, of course, a fair chunk of the Orient), but the ice ages weren't continuous; there were many warm gaps between them.

The mammals of the Pleistocene include what are surely the most familiar fossil mammals to most people, the ones we generally think of when we think of 'after the dinosaurs'. For this was the time of the mammoths and sabretooths. They're familiar to us because, aside from the tiny sliver of warm weather we currently live in, the Pleistocene is the most recent, and therefore the best preserved and the most easily analysed, of all the epochs of the Age of Mammals. It's been the setting for a number of films, books, and TV series - to name just two, the Ice Age cartoons, and the Earth's Children series.

Yet, when we think seriously about Pleistocene animals, there are a couple of important points to bear in mind.

Sharing Resources

Black-and-gold howler monkeys. The black one is male, the gold, female.

I've mentioned previously how animals have to juggle their time between different activities, such as feeding, watching for predators, and reproducing, and how that can be affected by things such as the size of the herd they live in (if any). Unsurprisingly, this works both ways, with the size of a herd being affected by the animal's lifestyle.

One of the main reasons for living in a herd is that it makes it easier to watch out for things that are going to try and eat you - you don't all have to be watching all the time, which means that each individual can spend more time eating, or doing whatever else it wants. So a herd has to be large enough for that to be worthwhile, and there may also be a minimum size on viable herds based on such things as the way the animal breeds. On the other hand, a really large herd is going to require a lot of food to sustain it, so the amount of food available is likely to put an upper limit on the herd size.

Weasels at Sea: Sea and Giant Otters

Sea otter mother with pup

Most otters are considered to be 'semi-aquatic' animals. That is, they spend most of their time swimming in rivers or lakes, where they catch the great majority of their food, but they return to dens on the bank in order to sleep and raise their young. However, there is one exception: an otter that is fully aquatic, and is, in fact, the only truly aquatic mammal to have feet, rather than flippers - all the others are seals, whales, dolphins, and the like. This is the sea otter (Enhydra lutris).

Most other otter species will enter salt water on occasion, especially if they live on small islands where fresh water is scarce. The marine otter is unusual in that it habitually hunts at sea, and only occasionally enters rivers, but it still creates dens along the shoreline, and so is considered only semi-aquatic. Generally when otters do swim in the sea, they avoid water that's any deeper than most rivers, and even marine otters won't venture more than about 150 metres (500 feet) offshore. Not so the sea otter.

Sea otters live along the coasts of the northern Pacific. In the south, they reach as far as California, and once even reached the west coast of Mexico, but the majority are now found off the southern coast of Alaska, and there are also sea otters along the coasts of far eastern Siberia and the extreme north of Japan. They are not close relatives of the other American otters (Lontra spp.), but are instead later arrivals on that continent, closer in origin to the various Old World species.

Age of Mammals: the Pleistocene (Pt 1)

A scene from northern Spain

The "Age of Mammals" is the informal name for the Cenozoic era, the 65 million year slice of Earth's history from the extinction of the dinosaurs to the present day. It is so named because mammals have been the dominant large, land-dwelling animals throughout the era.

Of course, "large, land-dwelling" is something of an arbitrary qualification, and one more rooted in the natural prejudices of our own species than in an actual reflection of Earth's biodiversity. The most numerous animals throughout the era, and, for that matter, through the Age of Reptiles that preceded it, would have been insects. But, unless you're standing in the middle of a swarm of midges, most people don't notice insects in the same way they would notice, say, a herd of antelope, or a prowling tiger. Mammals aren't even the most numerous vertebrates today, and, by sheer species count, it's the fish that are dominant, and some of those are pretty big.

Even on land, in terms of number of species, mammals are the least numerous of the four vertebrate classes - birds come in first, and reptiles still hold on to second place, followed by amphibians. Of course, most of those reptiles are small lizards, and birds are also generally quite small. Even so, there are ostriches, crocodiles, and anacondas, among others, and, in fairness, most mammal species are mouse-sized. So there's a reasonable case that what this should really be is the Age of Birds. But I, for one, am going to stick with the standard term.

Are Other Animals Ever Right-handed?

Humans normally display a preference for using one hand, rather than the other, for performing complex tasks, such as writing. It's most commonly the right hand, although exactly how common left-handedness is is debatable - largely due to insistence on the use of the right hand in some cultures, regardless of individual preference. While a small number of people are ambidextrous, this seems to be something that's learned, rather than something that you're born with.

Do other animals also display a similar preference? For most, that's a difficult, if not impossible, question to answer. A right-handed horse, for example, would prefer to use it's right front hoof to do... what exactly? When an animal has no manual dexterity to start with, we can't really say which side is the more dextrous. Studies looking at handedness in other animals have therefore focussed on those which are capable, to at least some degree, of grasping, and of performing tasks that are least somewhat analogous to how we use our hands.

Dire Wolves and Direr Dogs

Reconstruction of a dire wolf

[For more on dire wolves specifically, see: Dire Wolf Redux]

We are all familiar with the idea that, for much of the Age of Mammals, there have been large, scary cats with enormous teeth. They died out relatively recently, and as a result, we know a fair bit about them, and they remain one of the most popular prehistoric mammals with the general public - although mammoths do pretty well, too.

But, while the sabre-tooth cats stalked the world, what were the dogs like?

Perhaps the best known prehistoric dog is the dire wolf (Canis dirus). Do a google image search for "dire wolf" and you'll find far more images than you will searching for "sabre tooth", let alone something more specific like "Smilodon". But a look through those images gives you some idea why, and it doesn't have much to do with real-world fossils. The term "dire wolf" has been co-opted by fantasy fiction and games, and many of the pictures show the animals as they appear in Dungeons & Dragons, World of Warcraft, or Game of Thrones. They are generally portrayed as immense wolves, at least the size of a small horse, and sometimes with sabre teeth of their own, or bizarre spikes on their bodies.

Weasels in Warm Rivers: Otters of the Tropics and the South

Hairy-nosed otter

The body plan of otters is evidently a successful one in evolutionary terms. While the two species of "common otter" are the only ones inhabiting the rivers of the northern temperate zone, there are at least ten species in other parts of the world, and most of them look remarkably similar. They all have long, sinuous, bodies with short legs and webbed feet. Their tails, quite unlike the slender or stumpy appendages of other members of the weasel family, are powerful and muscular, and somewhat flattened to better help propel them through the water when swimming. Their fur is dense and, in most cases, short and sleek.

Furthermore, they are all more or less the same colour. Otters, of all species, are brown over most of their body, and they usually have paler underparts with a particularly noticeable patch of pale fur on the chest, which may extend up onto the chin. Compared with the variety of weasels, or even martens, the visible differences between most species of otter can be subtle, and it's hard tell them some of them apart.

The closest living relative of the familiar Eurasian otter is the hairy-nosed otter (Lutra sumatrana) of South East Asia and western Indonesia; the two species probably diverged during the early Ice Ages. It is also a highly endangered species, and, combined with its remote jungle location, that means we know relatively little about it. This story of threats to otters is, sadly, one I'll come back to a lot in this post. Of all the members of the weasel family, the otters are the ones most at risk, probably because their riverine habitat makes them particularly susceptible to pollution, and may also make them easier to hunt for their valuable fur.

Battle of the Sabretooths

Machairodus giganteus

The cat family is divided into two living subfamilies. One group are the pantherines, or large cats, which include lions, tigers, jaguars, and the various kinds of leopard. The other are the felines (which means that, in the technical, scientific sense, lions are not felines - the correct collective term that includes all members of the cat family is "felid"). The felines are quite variable in size, from cougars and cheetahs at the high end, through a range of mid-sized cats such as lynxes and ocelots, down to wildcats and their familiar domestic relatives.

But there once used to be a third subfamily of cats, and they represent, with the possible exception of mammoths, what are probably the most widely known of all extinct mammals. In fact, I'd guess that they are the only extinct mammals that come at all close to dinosaurs in terms of popularity. I refer, of course, to the sabretooth cats.

Chances are, especially if you're American, the sabre-tooth cat you've heard most about is Smilodon. This is actually three different species of cat, albeit very closely related. The largest was about the size of a lion, but with a short tail, like a bobcat. They used to live in both North and South America, and died out only around 10,000 years ago, perhaps not coincidentally shortly after humans became numerous on those continents. (Not, one assumes, that humans would have hunted Smilodon themselves - but they may well have eaten much of the cats' preferred prey).

News in Brief #5

Mountain long-eared bat

Can Bats Fly Like a Bird?

This is a blog about mammals, so it's only right to point out, every now and then, that birds have no monopoly on animal flight. The only mammals capable of true flight are, of course, the bats - flying squirrels and their ilk can only glide, not truly fly. (Nor are mammals and birds alone, of course; there are many flying insects, and once upon a time there were also pterosaurs). Still, birds have been flying for much longer than bats have, so might they be better at it?

A recent study by Florian Muijres and colleagues reveals, perhaps surprisingly, that the answer is 'yes'. They put birds and bats in a wind tunnel, and measured their ability to generate lift, and the lift-to-drag ratio, which indicates how much energy they have to put into it. By both measures, birds outperformed bats of similar size. Why so? After all, while birds have been flying for three times as long as bats have, the oldest known bat fossil is still very old, and you'd think they'd be pretty good at it by now.

Being a Little Bit Pregnant

Sun bear

In my ongoing series on the members of the weasel family, I have, on a number of occasions, referred to the concept of delayed implantation. A number of members of the weasel family exhibit this phenomenon, and they are far from alone among mammals.

To begin with, the egg cell starts to divide immediately after fertilisation. In most mammals, it then rapidly forms into a hollow ball of cells that move down through the reproductive tract into the womb. During this time, it really doesn't change much in size; the ball of cells, known as a blastocyst, is not much larger than the unfertilised egg, and the individual cells within it are much smaller.

Once it reaches the womb, the blastocyst attaches itself to the uterine lining and begins to send out tiny tendrils of cells that penetrate the wall in search of blood vessels. Once it finds them, the embryo can obtain nutrients from the mother, and starts to grow and develop. The side of the structure in contact with the uterine lining develops into the placenta, while the remainder forms the embryo proper, and the amniotic membranes surrounding it. This even occurs in marsupials, although, in their case, the placenta is primitive and short-lived, and, for that matter, there's something similar in some reptiles, such as sea snakes.

The Importance of Grooming

Primates are amongst the most social of mammals. They tend to gather together in bands or aggregations, often based on female kinship, and with a relatively small number of dominant males, born outside the group. The details vary considerably between species, as we might expect, but one feature that is relatively common is the way that such social bonds are formed and cemented. A particularly common way that primates maintain these bonds within a group is through grooming.

In grooming, the animals pick through a partners hair, removing lice, ticks, and other parasites, and generally keeping each other clean. This has obvious health benefits, and, in fact, these may be wider than is clear at first glance, since there is evidence that grooming causes the release of endorphins, hormones that, in humans, reduce pain and generate a feeling of well-being. Probably as a result of this, in at least some species, monkeys with better social relationships apparently live longer and have healthier offspring than those who feel more isolated.

Such benefits generally apply to the recipient. What does the animal performing the grooming from the practice? The most apparent and immediate benefit is that the other animal may groom you back, so that everyone benefits. Indeed, it's entirely possible that we humans don't cement social bonds this way simply because we haven't got the fur to make it worthwhile. But, given the complex, and non-egalitarian, social lives of most primates, there might be other benefits as well, which could explain why it's not simply the case that every monkey in a troop grooms every other one equally.

Weasels in Cool Rivers: The Common Otters

Eurasian otter

The otters are, arguably, the least weasel-like of all the members of the weasel family. Although the relationship has been clear for a long time - the first scientific description of an otter, by Linnaeus in 1758, actually placed it in the genus Mustela, to which stoats and weasels belong - so have the differences. As early as 1771, Danish zoologist Morten Thrane Brünnich split them off from their fellow mustelids, erecting the new genus Lutra to describe them.

By 1838, at least three genera of otter had been described, and the group were raised to 'subfamily' status to distinguish them from their terrestrial kin. Other subfamilies were erected later, largely to distinguish the badgers, but the otters have remained as a clearly distinct group within the overall weasel family.

Genetic studies in the last four years have given us a much clearer picture of how the various kinds of mustelid are related to one another, and it turns out to be more complicated than we thought. For example, martens turn out to have been around longer than otters have, which was something of a surprise. The otters, however, survived the revision unscathed, confirmed as a genuine evolutionary group, albeit one that is younger than we might have guessed. Their closest relatives within the family turn out to be the mustelines, the group that, among others, includes the semi-aquatic mink.

Dugongs of Italy

Metaxatherium floridanum, a Caribbean species

Three different orders of mammal include at least some species that have returned to the sea. Of these, perhaps the best adapted at the cetaceans, including the whales and dolphins. All cetaceans are carnivores, feeding on various aquatic animals, ranging in size from krill to their fellow cetaceans, and often doing so far from land. Similarly, seals and some species of otter spend much of their lives at sea, and they, too, are carnivores - mostly feeding on fish, although some tackle other prey, such as penguins. This is unsurprising because, aside from plankton, there isn't generally a lot of plant matter far out at sea, and mammals generally aren't as good at eating plankton as fish are.

But the third group of truly aquatic mammals are, in fact, herbivorous. These are the sirenians, and there are only four species alive today. Three belong to the manatee family, including one species that lives off the southeastern coast of America. The fourth is the dugong (Dugong dugon), an inhabitant of coastal waters around the Indian Ocean and into the western Pacific. The dugong is the only living member of its family, and, like manatees, it inhabits shallow waters because there, the sunlight can reach the seabed and permit the growth of the seagrasses that it eats.

Does Colder Mean Bigger?

Amne Machin, Qinghai

In 1847, German biologist Christian Bergmann formulated what has since become known as Bergmann's Rule. Over the following 165 years, the Rule has been somewhat modified and re-interpreted from Bergmann's original statement, but a common modern version is that warm-blooded animals tend to be larger the colder the environment they live in. Bergmann was originally thinking of closely related species; for example, polar bears tend to be larger than most brown bears. However, the rule is now often applied to individuals and populations within species; for instance, Siberian tigers are larger than those that live in the tropics.

The rule has, as I've noted before, been the focus of some controversy. Is it, in other words, actually true? Certainly, there are many counter-examples - snow leopards are the smallest cats in their genus, for example. But are these rare exceptions to a general rule?

Making your Mark

For most humans, the dominant sense is that of vision. Although the other senses are important, vision is particularly important to us, and it is generally well-developed in other primates, too, perhaps because most of them spend a lot of their time swinging through trees, where a good idea of the location of nearby branches is definitely helpful. But, for most mammals, the sense of smell is much better developed than it is in us, and far more important to the way they interpret the world.

One of the many ways that they make use of this is through scent marking. Apart from those that spend most of their lives in the water, the great majority of mammals scent mark in some way, and humans are a bit of an oddity in this respect. To assist them in scent marking, many mammals possess special glands producing smelly secretions that they can place on prominent landmarks, or in other locations that fellow members of their species might come across. And, of course, any cat or dog owner is familiar with the concept of using urine as a mark - the urine contains unique chemicals that can provide far more information to the animals concerned than it does to us.

The actual purpose of scent marking varies depending on the nature of the animal, and, particularly, its lifestyle and habits. For many animals, it can be used to stake out patches of territory, or to advertise sexual receptivity, for example, and that will depend both on how the animal claims territory, and on the details of their mating habits, such as how promiscuous they might be.

Along with polar bears, brown bears (Ursus arctos) are amongst the largest of all carnivorans. Like many carnivores - although unlike, say, wolves, lions, or otters - they are solitary animals as adults. Scent marking is therefore particularly useful for them, allowing them to record their presence and leave information for any other bears that may happen to wander through the same area. However, they are not particularly territorial. They do, like most other mammals, have a "home range" through which they habitually travel, but this regularly overlaps with those of other bears, of either sex, especially where food is abundant, and several bears live relatively close together.

Weasels in the Tundra and the Jungle: Wolverines and Tayras

The largest terrestrial member of the weasel family is the wolverine (Gulo gulo). Indeed, by the standards of weasels, it's exceptionally large, around twice the weight of badgers, and about three feet long, not counting the tail. Within the weasel family, it belongs to the same evolutionary branch as the pine martens and their kin, and, size aside, that is apparent in its appearance.

Compared with martens, however, the wolverine is not only larger, but stockier, and much of its weight - three times that of the next largest marten-like animal, the fisher - is muscle. Indeed, they may well be the most physically powerful of all mammals in their size range. Other martens vary in the degree to which they live in the trees, but wolverines are the most terrestrial of them all, although they remain capable of climbing trees when the need arises. Compared with other marten-like animals, they have flat-soled feet, which are large and furry, making them ideal for running on snow. They also lack the pale 'bib' commonly seen on the throat of martens, although there is generally a band of paler fur running across their flanks to the base of the tail. Their fur is also exceptionally thick, which makes them look even larger than they are.

The Horns of Early Rhinos

Indian rhino (Rhinoceros unicornis)

There are just five living species of rhinoceros, the second largest land animal, after the elephants. Three of those species are on the verge of extinction, and neither of the other two is entirely safe. Yet, as is so often the case, these five species are but the last remnants of a group of animals that was once much more numerous. Rhinos, or their close relatives, once wandered across much of the world, from the tropics to the edge of the Arctic, and they were found, not only in Africa and Asia, where they are found today, but also in Europe and North America.

How many different kinds there were depends, in part, on what you consider to be a rhinoceros. Today, there isn't much else that's like a rhino. Their closest living relatives are the tapirs, but, while there are a number of anatomical similarities (a similar digestive system, placing most of their weight on their middle toe, and so on), you'd never confuse one for the other. Indeed, tapirs and rhinos are not particularly close, probably having last had a common ancestor in the early Eocene, almost at the beginning of the Age of Mammals.

Since that time, the evolutionary line that led to modern rhinos has developed on its own, and into a much wider range of forms than the modern species might suggest. It's generally agreed now that there were at least three different families of rhinoceros-like animal; one of them long-legged and relatively swift, one semi-aquatic with a vague resemblance to hippos, and one that contains the "true", living, rhinos.

The Life of an Endangered Porcupine

Porcupines are among the most distinctive of all rodents. With their combination of long quills, long tails, and large rodent teeth, they're pretty difficult to mistake for anything else. However, there are actually two families of porcupine, which are not directly related to each other, and which live on opposite sides of the Atlantic Ocean. The porcupines of Africa and Asia and those of the Americas are different in a number of ways; perhaps most notably, the American ones live up trees, while those elsewhere live only on the ground.

Of all the porcupines, though, one of the strangest is the thin-spined porcupine (Chaetomys subspinosa) of eastern Brazil. Although it was first described way back in 1818, for most of the twentieth century, no scientist had even seen one, until a survey in 1986 confirmed their continued existence. Much smaller than other porcupines, and more bristly than spiny, there has been considerable debate as to whether it even is a porcupine. Instead, it's been argued that it might actually be a type of animal called a spiny rat, another fairly odd family of rodents which it does certainly resemble.

The question was settled in 2009 when genetic and chromosomal studies proved, quite conclusively, that it is a porcupine, albeit an unusually small and rat-like one. Indeed, its ancestors seem to have separated from those of all other American porcupines as far back as the early Miocene, around 20 million years ago. In comparison, the next branch we know of within the family is the split between the North American porcupine and its assorted South American cousins around 10 million years ago, with all the other branches being considerably more recent than that.

News in Brief #4

A Rat's Idea of 'Vermin'

Arguably the most important factor in the success of humanity as a species is out ability to modify the environment around us, to take somewhere inhospitable, and not only make it habitable for our species, but enable it to support far more humans than any natural environment possibly could. The existence of cities, and of the great swathes of agricultural land around them are clear testaments to modify the world to the point of creating entirely new environments.

We may be the most spectacular example of a species that can do that, but many others do so, albeit on a smaller scale. They're not all mammals, or even vertebrates - consider termite mounds, of example. Often, the way that one species modifies it environment also helps others, whether intentionally, as in humans providing farmland for cattle, or as an unavoidable by-product, such as humans creating the perfect habitat for rats. This process is called "facilitation", and it seems to have been more studied in botany than it has in zoology.

However, Andrew Edelman, of the University of New Mexico, has been looking at the interaction between two animal species in the Chihuahuan Desert. Banner-tailed kangaroo rats (Dipodomys spectabilis) are, like many rodents, seed-eating herbivores. They make large mounds in the desert in which to live, and, while they're generally pretty anti-social, not letting other rats near their homes during their lifetime, the mounds can nonetheless be passed down from rat to rat for generations, sometimes surviving for over fifty years.

Why Rabbits Aren't Rodents

Beaver skull

Over one third of all mammal species are rodents. By almost any reasonable measure, they are the most successful of all the mammalian orders. There are rodents everywhere, in every environment, and on every continent except Antarctica. There are even rodents native to Australia; they're the only placentals of which this is true, other than dingos and bats. They have even adapted, better than any other non-domesticated mammal, to life in urban environments. Indeed, the natural habitat of the house mouse is, pretty much, houses - presumably they used to live somewhere else at some point (river banks, probably), but not really any more.

However, that's going by the scientific meaning of the word 'rodent'. In everyday speech, I've heard the term applied to a even wider range of animals, including such things as shrews, but, most commonly, rabbits. Yet rabbits, along with hares and pikas, are not rodents. On close examination, it doesn't take much to demonstrate that, despite their size and shape, shrews aren't rodents, but rabbits... well, rabbits are pretty rodent-like. So what's the difference?