Running Hyenas of Greece

Chasmaporthetes

Mentioning a "hyena" today likely brings to mind the image of a muscular, aggressive, scavenging creature, probably with a spotted coat. This, the spotted hyena (Crocuta crocuta), is, however, only one of three species alive today, with the two lesser-known ones being smaller and less aggressive. In fact, the hyena family includes a fourth living species as well, although this isn't always referred to as a "hyena" because it's really only dangerous to termites and can't crack bone like "true" hyenas can.

Four living species isn't very many for a family of mammals but, like many other such small groups, there is a long fossil history that includes a great many extinct forms. These varied in form even more than the living species do. At one extreme are animals larger and stronger even than the living spotted hyena, while at the other (all living very early on) are small tree-climbing animals that looked more like civets. 

Somewhere in between are the "running hyenas".

The Diets of Parallel Pigs

Peccaries from South America

The word "ungulate" refers to a broad category of mammals that are generally large and herbivorous. They form a natural evolutionary group, although only if you include the cetaceans, which are descended from vaguely hippo-like ancestors. The word comes from the Latin word for "hoof", and the great majority of living ungulates have hooves of one kind or another. Even ignoring the cetaceans there are exceptions, but it doesn't take a great stretch of the imagination to see that camels, for instance, are at least the same general kind of animal as deer or cows.

All living ungulates can be placed into one of two mammalian orders: the artiodactyls, which includes the cloven-footed kinds, and the perissodactyls, which includes, among others, the horses. If you start looking at fossils, however, it becomes clear that other ungulate orders once existed. Most were very early, dying out in the first half of the Age of Mammals, representing early branches in the great ungulate family tree that ultimately proved unsuccessful.

Hammer-Toothed Snail Eaters

As is true of mammals more generally, the majority of Australian marsupial species are herbivorous, including such familiar animals as kangaroos, wombats, koalas, and possums. (The latter, of course, are not to be confused with the American opossums, which are omnivorous and not very closely related to their Australian namesakes). Most, but not all, of those that are not belong to a single order, the dasyuromorphs, sometimes called the "carnivorous marsupials" for this reason.

Although they represent almost a third of non-American marsupial species, dasyuromorphs are far less diverse than their herbivorous counterparts, with all but one of the living species belonging to a single family, the dasyurids. Although the most famous example of the dasyurids is probably the Tasmanian devil, which eats comparatively large prey, most of the other species are small shrew-like animals feeding on insects. Alongside them, we can place the numbat and the extinct thylacine ("Tasmanian tiger" or "wolf") both of which are odd enough to be placed in families of their own.

Vishnu's Otter in Bavaria

Otters are members of the weasel family, something that has been recognised since the dawn of taxonomy in 1758, when Linnaeus placed them in what was then the weasel genus (taxonomic families not yet being a concept). Their adaptations to the water, including their powerful muscular tails, were long thought significant enough that they were separated out into a distinct subfamily, a position they still retain, although it turns out that they are more closely related to the weasels proper than to some other members of the family such as, say, pine martens or wolverines.

Perhaps because rivers are a good environment for forming fossil-bearing sites, we know of a significant number of fossil otters and, most of them would doubtless have been instantly recognisable as otters were we able to see them in the flesh, there is perhaps more variety amongst them than we might at first expect. For example, a number of them are quite large - in some cases, larger even than the "giant otter" (Pteronura brasiliensis) of today's Amazon, the largest living member of the weasel family. (So, yes, it's bigger than a wolverine).

How Walruses Got Their Tusks

Titanotaria, a tuskless walrus

Few people would argue that the walrus (Odobenus rosmarus) is not a distinctive animal. Indeed, it is so distinctive that, despite there being only one living species, that species has been placed in a "family" all of its own since 1880, distinct from both the seals and sea lions. 

There are a number of features of walruses that make it clear, from a modern perspective, that this was the right decision to make. But the most obvious is surely that they have huge tusks. These are in many ways a remarkable feature, and while other animals, such as elephants, also have large tusks, none that's alive today has anything quite like those of the walrus. 

Walruses have a long evolutionary history, having been distinct from their closest living relatives for many millions of years. Nonetheless, those relatives are, as we might expect, the seals and sea lions and it's apparent that they entered the water long before growing the tusks. Which, in turn, means that the first walruses must have been tuskless. So when and how did this change?

Miocene (Pt 11): Horses on the Grasslands

Daeodon

The lush greenery of Early Miocene North America was a good place for large mammalian herbivores. Many of these, such as musk deer, pronghorns and camels, were, in one fashion or another, cud-chewing animals, able to extract maximum nutrition from a grassy or leafy diet. But many, of course, were not, either finding different ways to get the most out of their food, or else going for plants that were generally easier to digest.

Some of these were, like the ruminants, cloven-hoofed animals. Today, the main group of non-ruminant cloven-hoofed animals are the pigs, but they have never truly lived wild in the Americas, with feral 'razorbacks' only having arrived with the white man. Instead, America has peccaries, also known as javelinas, animals that look very much like pigs, but have a number of crucial differences.

The Pig Family: The Strange Case of the Sulawesi Pig-Deer

Sulawesi babirusa

Warthogs are fairly odd-looking animals, as are forest hogs, among others. But, at least to my mind, when it comes to wild pigs, nothing quite beats the babirusas.

These strange looking pigs inhabit the island of Sulawesi in Indonesia. Unlike most of the others in the group, this has been an island for far longer than pigs have been in existence - when sea levels were lower, most islands to the west were joined with Asia, and those to the east with Australia, but the waters around Sulawesi are so deep that it remained isolated. I've mentioned this before, in the context of warty pigs, so it's interesting to note that those channels must have been crossed by wild pigs on no less than three occasions (the third sort of Sulawesian pig, Celebochoerus, died out in the Ice Ages).

The Fast Lives of Early Sperm Whales

Livyatan melvillei, a Miocene species
(It was supposed to be 'Leviathan', but the name was
already taken)

Sperm whales are magnificent and highly distinctive animals. While they may not be quite as large as the great toothless whales, they are still pretty huge: a fully grown male is typically about 16 metres (52 feet) in length and weighs over 40 tons. So distinctive is it, in fact, that today it is usually considered to be the only living species in its family, the Physeteridae.

The caveats in that last sentence - "today", "usually", and "living" - are all significant. On the first two points, the sperm whale family used to be considered to contain no less than three living species, and some researchers still define it that way. The other two species are the dwarf and pygmy sperm whales (Kogia spp.), and they're typically (but not always) placed in their own family these days. As their names suggest they are much, much smaller than the "true" sperm whales, being more like the size of a large dolphin.

Toothless Old Fossils

Artwork depicting extinct animals almost invariably shows them physically fit, unless they're actively engaged in some life-or-death battle. They're usually either adults in the prime of life, or still juveniles (often newborn). And this is actually quite reasonable, since few animals get to live to an old age out in the wild. Most will, after all, be eaten before then, and if they have any serious illness or crippling injury, they're not going to last long. Senescence, the gradual decline of biological function associated with becoming elderly, is not something we see much in the wild, for all that it's common in humans and domestic animals.

Which isn't to say that we don't see it at all, especially in very large animals that have few, if any, natural predators once they reach adulthood. The same must also have been true in the distant past, and it's reasonable to assume that at least some fossils, at least of the larger animals, belong to elderly individuals. It isn't, however, necessarily going to be all that obvious, especially if the skeleton is incomplete in the first place. Nonetheless, a recent report does describe a jawbone that the authors believe belonged to an elderly animal, and, if they're right, this offers some unusual insights into the creature in question.

The Teeth of Dead Kangaroos

Not exactly lush vegetation

How to tell what long-extinct animals ate?

Aside from those that died recently enough to leave us mummified, rather than fossilised, remains, your best bet is probably fossilised dung. In the case of carnivores you might even be lucky enough to find the bones of their kills. Of course, both do need matching up to the correct animal, but the former, in particular, is not especially common. Absent such direct clues, then, we have to deduce what we can from the skeleton, and that generally means examining the teeth.

The overall shape of the teeth can give us some pretty clear indications of whether an animal was a carnivore or a herbivore. This is even more true for mammals than it is for dinosaurs, since we have plenty of clear examples alive today. Powerful stabbing canines and flesh-shearing molars indicate a carnivore, while flat grinding plates and leaf-clipping incisors imply a herbivore. There's obviously some gradation in between, in the case of omnivores, insectivores, and, for that matter, weird specialists such as vampire bats, but it's a good starting point.

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.

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.

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?

Grazers and Browsers - and how to tell them apart without watching

Wildebeest are grazers - note the squarish muzzle

One advantage of studying the fossils of prehistoric mammals, as opposed to dinosaurs, is that mammals are still around today, while non-avian dinosaurs aren't. That gives us the ability to compare fossil species with living ones, and be fairly confident that our comparisons make sense. That's not to say, of course, that we can't infer quite a lot from the shape and structure of dinosaur bones, and work out details of their lifestyle and habits. But there's nothing much like non-avian dinosaurs around today, so there will inevitably be some guesswork involved when we do - educated guesswork, to be sure, but guesswork none the less.

Although the same can be said of fossil mammals - especially the stranger ones - in many cases, we can be more confident that our educated guesses are likely to be accurate. For example, sabre-tooth cats were, well... cats. So we can look at, for example, the proportions of their limbs, compare them with living cats, and deduce whether they were more like, say, jaguars, than they were like  leopards. Because leopards, jaguars, and sabre-tooths are, in many respects, quite similar, it's pretty likely that inferences drawn from the first two will apply to the third, unless there's some good reason to suppose otherwise. We know what cats are like, and sabre-tooths were cats, so that tells us a lot.

And what about herbivores? Herbivory includes a range of different diets, such as animals that feed mainly on seeds, or fruit. But large mammalian herbivores tend to have two possible feeding strategies: grazing and browsing. The best way to tell the two apart would be by examining their dung, and, failing that, the structure of their digestive systems could well be helpful. Neither, of course, are possible, if all you have is a fossil skeleton, but, fortunately, there are other clues we can examine.

Carnivores, Carnivorans, and Carnassials

Some time ago Irregular Webcomic ran, as one of its occasional polls the question "What do you consider the defining characteristic of a carnivorous animal?" Most of the answers, as you might suppose, centred around the extent to which the animal ate meat. But almost 10% of respondents replied "a member of the order Carnivora."

Now, this has to be interpreted in the context of an earlier poll which, in a game of twenty questions, asked whether the subject of the game was carnivorous or not, it having already been established that the animal was mammalian. If people were interpreting the later question in light of that, rather than answering the actual question as written, we might suppose that they were mentally ruling out anything non-mammalian. Otherwise 10% of IWC readers must think that, for example, crocodiles and sharks are not carnivorous. Which seems a bit unlikely.