The Patagonian Homunculus

In 1891, Argentinian naturalist Florentino Ameghino, the founding father of South American palaeontology, described a new species of fossil primate. Naming it Homunculus ("little man"), he recognised that it resembled a lemur almost as much as a monkey and must therefore be very primitive, but he was unable to categorise it further.

To be fair, all he had at the time was a section of the lower jaw. Over the next seven years, working with his brother Carlos, he uncovered a few further specimens. These included part of a skull and some limb bones, but the exact details of what they had discovered remained obscure, beyond the fact that it was a primate of some sort.

It didn't help that, after 1898, the next discovery of a fossil belonging to the genus didn't happen until the 1980s. And that was only a few isolated teeth. Since then, nothing until the current century.

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".

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. 

Attack of the Giant Hyenas

Dinocrocuta

I suspect that most non-specialists would assume that hyenas are fairly closely related to dogs. They certainly look more like dogs than they do anything else, so, absent any further information, that seems reasonable enough. But, in reality, hyenas belong to the cat-like, not the dog-like, branch of the carnivoran family tree.

This isn't some new discovery on the basis of molecular evidence, like the splitting off of the skunks from the weasel family; it's been known for a long time. This is because, when you start looking at the structural details of the skull, especially the area around the ear, everything fits with a cat-like ancestry. This much was already obvious when Miklós Kretzoi formally named the two carnivoran branches while he was working at the National Museum of Hungary during World War II. Modern evidence has merely confirmed the view, showing more precisely that the closest living relatives of the hyenas are the mongooses.

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.

The Pandas of Bulgaria

The bear family as it exists today contains relatively few species. All but two of these species are placed in a single subfamily, the ursine bears, which includes the familiar black, brown, and polar varieties along with a couple of species unique to southern Asia. A second subfamily, the short-faced bears, includes the living spectacled bear of South America and several, often exceptionally large, fossil species. They are thought to have split from the ursine bears around 12 million years ago, towards the end of the Middle Miocene. The third living subfamily is both much older and more distinctive.

This, of course, is the subfamily of the pandas, the Ailuropodinae. Pandas are sufficiently odd that it was unclear for a time whether they were really bears, or something else, although their status hasn't really been in doubt since the 1980s when genetic evidence proved what had, even then, been suspected for a couple of decades. Today, only one species of ailuropodine exists, the giant panda (Ailuropoda melanoleuca), and it is found only in China. The same evidence used to estimate the split between the other living subfamilies puts the date of the split between pandas and other bears much further back, to around 20 million years ago, not long after the dawn of the Miocene. 

The Dolphins of Switzerland

Kentriodon

The Mediterranean is very nearly an inland sea. Its only natural connection to the world's wider oceans is through the Strait of Gibraltar between Spain and Morocco, a passage just 13 km (8 miles) wide at its narrowest point and in places just 300 metres (1,000 feet) deep; pretty shallow as such things go. It's probably because of this that some of the larger whales that inhabit the Atlantic (blue whales, humpback whales, etc.) are rarely if ever seen venturing into its waters.

Dolphins are a different matter, with the majority of North Atlantic dolphin species also being commonly seen in the Mediterranean, albeit in some cases only in its most westerly waters. This includes some of the really big dolphins that we'd normally call "whales", such as the killer whale, and there are three species of genuine whale that live there, too. The connection between the Mediterranean and the Atlantic has not always been there, however; for a long time during the Late Miocene, the two bodies of water were separated by a land bridge between Spain and Morocco, entirely cutting the Mediterranean off until it ended in the cataclysmic Zanclean Flood. 

Brains of the Monster-Teeth

Dissopsalis, another member 
of the "monster-tooth" family

Among the distinguishing features of mammals, as compared with other vertebrates are the larger relative size and greater structural complexity of the brain. It's worth pointing out at the outset that many birds are as capable as mammals of complex behaviour despite not possessing the brain structures we'd otherwise associate with such things so that we can't solely use brain anatomy as a proxy for things like 'intelligence'. But, if we're looking only at mammals, brain anatomy can tell us quite a bit and it's probably fair to say that it does distinguish us from, say, reptiles.

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?

Miniature Marsupial Lions

Thylacoleo carnifex

The largest carnivorous marsupial alive today is the Tasmanian devil (Sarcophilus harisii). Noticeably smaller than a European badger, it's still almost twice the weight of the next nearest contender for that title, or, indeed, of the omnivorous Virginia opossum so well-known to Americans. Most other living predatory marsupials can more accurately be described as "insectivores", due to their small size.

Unsurprisingly, this wasn't always so. Most famously, perhaps, there was the thylacine or Tasmanian wolf, which officially went extinct in 1936. There were also the "marsupial sabretooths" of South America, which died out during the Pliocene about three million years ago. However, these are no longer thought to technically be marsupials in the sense of being descended from the last common ancestor of the living species, even if they were definitely in that branch of the mammalian family tree.

The Beaches of Bakersfield

Modern walrus skull

Seals have a moderately long fossil history, with some of the oldest examples dating from Europe, around 15 million years ago. Although they are now found worldwide, back in those early times, they seem only to have lived in the North Atlantic, reaching the Pacific only around 11 million years ago (probably by the simple expedient of swimming through the seas that then covered what is now Central America).

However, one of the world's best fossil sites for recovering fossil aquatic mammals is at Sharktooth Hill, just outside of Bakersfield, California. Part of the larger Temblor Formation, the deposits here consist of silts and sands, laid down just over 15 million years ago, when California was sweltering in the Middle Miocene Climatic Optimum, a time of unusually high worldwide temperatures - and correspondingly high sea levels. This was before seals had reached so far west, but that does not mean that a number of similar animals did not already live there at the time.

False Deer-Llamas of Bolivia

Theosodon
(the nasal bones are that 'bump' on the forehead
just forward of the eyes)

Australia is an island continent, separated from the rest of the world's landmass for millions of years, allowing it to develop its own unique wildlife, from kangaroos and wombats to bandicoots and emus. The only other island continent we have today is Antarctica, which has no native land mammals at all (or emus, obviously).

In geological terms, however, South America was also an island continent until relatively recently, only joining North America three million years ago, towards the end of the Pliocene epoch. Even today, the strip of land connecting the two is only 35 miles (60 km) or so wide at the narrowest point, both narrower and longer than that connecting Eurasia to Africa. This means that, like Australia, South America had a long history of so-called "splendid isolation", and it evolved a number of unique animals in the process.

Miocene (Pt 3): The Elephants Reach Europe

Gomphotherium angustidens

At the dawn of the Miocene, Europe was still relatively isolated from much of the rest of the world. The only other continent to which is was attached by land was Asia, and even with that, perhaps due to the higher sea levels and narrower land bridges of the day, there was less exchange of animals than one might expect. As a result, for a few million years at the dawn of the epoch, Europe remained a haven for animals that had died out elsewhere, or at least retreated. Tapirs, for example, were still common; today they are restricted to South East Asia and the Americas. The European rhinos of the day were also relatively small and primitive.

While the millions of years that they survived might actually have been quite notable, had we been talking about the much shorter, later epochs, in the grand sweep of the Miocene, we can say that they were quite rapidly replaced by immigrants from the east. The early tapirs were gone (although more modern forms did return for a while, much later), but the rhinos were instead replaced by larger and more sturdy, distinctly Miocene species.

When the Hippos Changed

The hippopotamus family contains just two living species, including, of course, the well-known common hippo (Hippopotamus amphibius). As is so often the case, though, the family has a long fossil history including a number of other species and genera, although, while the fossil species were more widespread than the living forms are today, it's fair to say that it was never a huge or diverse group in the way that, say, antelopes are.

Among the fossil species, several are very closely related to the living common hippo, including both the stalk-eyed hippo (H. gorgops), which probably weighed over 3 tonnes, and the pig-sized Maltese hippo (H. melitensis). Quite where the living pygmy hippo (Choeropsis liberiensis) fits in the fossil family tree is much less clear, but there are a number of species that aren't particularly close to either of the surviving forms.

Taking a broad view of the fossil history of the family, then, palaeontologists have tended to group the hippos into two subfamilies. One are the "hippopotamines", a group of broadly "modern" hippos that includes both of the living species. At least two other genera are also considered to belong to this group, one of which, Hexaprotodon, lived everywhere from Madagascar to Spain and Indonesia, taking in much of northern Africa and southern Asia on the way. Most of these lived during the Pleistocene and Pliocene epochs, which is to say, the Ice Ages and the epoch immediately preceding them. The earliest forms, including the other genus, Archaeopotamus of Kenya and Arabia, lived during the late Miocene, first appearing somewhere around 8 million years ago.

Miocene (Pt 2): Before There Were Mice

Heteroprox

After a brief cold snap at the very dawn of the epoch, the world of the Miocene warmed rapidly. Europe became, if not truly tropical, at least subtropical, with the interior covered by great forests of oak, laurel, and cinnamon, with magnolia and figs joining pine trees in the highlands. Along the coasts, the hot, damp, climate encouraged the growth of mangrove swamps and palm trees as warm sea currents flowed in from the Indian Ocean - still connected to the Mediterranean at this time. With no ice caps at the North Pole, and relatively few at the South, sea levels were much higher, and parts of continental Europe may, in those days, have still been islands. Certainly, Aqutaine in south-western France and the lower Rhône valley in the south-east were shallow bays stretching some way inland, as was what is now the Tagus valley in Spain and Portugal.

This rich and verdant landscape was home to a wide range of animals, many of them survivors of even earlier times. Many of these, such as the tapirs, didn't survive long in Europe, but a great many did, with musk deer, pigs, and rhinos dominating the herbivorous fauna, and animals less familiar to modern eyes taking the lead among the large carnivores.

But then, as now, the great majority of mammal species were small. While the sight of Diaceratherium rhinos wallowing in the lush swamps of the Swiss shoreline is the sort of thing that would draw the immediate attention of a time-travelling tourist, there was also plenty going on underfoot. Yet the two most common groups of small non-flying mammals that we have in Europe today - the mice and the voles - did not yet exist. So what was there?

Age of Mammals: The Miocene (Pt 1)

Five years ago, I started a series of posts in which I looked at the world, and its mammalian fauna, during the time of the Ice Ages. My plans as to how I was going to do that changed quite rapidly, and the earlier posts aren't really in the same format that I later settled in to. Nonetheless, since that time I have covered not only the Pleistocene epoch of the Ice Ages, but also the Pliocene, which immediately preceded it. Yet, even taken together, these two epochs represent only a relatively short slice of the Age of Mammals.

We currently divide the Age of Mammals - the time since the extinction of the non-avian dinosaurs - into three broad periods: the Paleogene, Neogene, and Quaternary. The last of those includes only the Pleistocene and the brief, human-dominated, time since it ended. The Neogene, however, is also dominated by more-or-less modern kinds of animal, and it is further divided into two epochs: the later Pliocene, which I have already covered, and the earlier Miocene, which I haven't.

Perhaps the first thing to grasp about the Miocene is that, compared with the epochs that followed, it is remarkably long. It lasted, as currently defined, from about 23 million to 5 million years ago. That makes it over three times as long as the Pliocene and Pleistocene put together. As you might expect, the world changed far more over this timespan than it did during the subsequent epochs; we're not just talking a couple of million years here, but it a much more substantial chunk of time. It's only because it's so much further back that it makes sense to do this - we just don't have the same sort of fine detail available, since so much of it has been erased in the time since it all happened.

The Largest Weasel Ever?

The weasel family were the first group of mammals that I decided to spend a year describing in detail on this blog, back in 2011-12. I concluded the series with a look at their fossil history, stating, among other things, that the fossil genus Enhydrodion "may" have been the largest member of the family to have lived. This, however, relies on guesswork relating the size of the body of the animal to its skull, which is all we have in any completeness. But there are, in fact a number of other fossil members of the family with even larger skulls, so a lot rests on their exact bodily proportions, which are often a mystery.

Such examples include the giant wolverine Plesiogulo (for which we have not only the skull, but, just possibly, the penis bone), the giant hypercarnivorous honey badger Eomellivora, and the relatively long-legged Ekorus, whose relationship to other mustelids is unclear. But, according to a new analysis, the largest mustelid skull known belongs to an animal called Megalictis ferox.

Of course, calling Megalictis a "weasel" is a bit of a stretch. The weasel family is very diverse, including such animals as otters, badgers, and wolverines, as well as more obvious examples such as polecats and stoats. So, yes, it's really only a weasel in the same sense that a badger is... and that's assuming it's a member of the weasel family at all. So, let's start with that - what is this animal, and is it really a mustelid?

Teeth of the Giant Honey Badger

Skeleton of a modern honey badger

Honey badgers (Mellivora capensis) have something of a reputation as particularly fierce animals. As is often the case, the reputation is somewhat exaggerated, but it isn't entirely false, either, and they are rather more purely carnivorous than the European badgers of Hufflepuff fame. They are, of course, members of the weasel family, on which I have posted at some length before, and, these days, are usually considered distinct enough to warrant their own subfamily within that group.

According to one study of the evolutionary relationships between mustelids, honey badgers represent one of the earliest branches of the weasel family tree. Assuming a relatively constant rate of genetic change between species after they diverge, and calibrating with the ages of some known fossils, the same study estimated that they should have first appeared about 11 million years ago, during the mid Miocene epoch, and probably in Asia. Naturally, for most of that time, they would not have been the same species that they are today, something that likely arrived much later - it's just that none of their closer relatives survived until the present day.

Tuskless Walruses of Japan

There are a number of mammal "families" that contain just one living species. Of course, what constitutes a "family" of animals is an arbitrary distinction, rather like the one that says Pluto isn't a planet. So, really, all we're saying is that there are some mammal species that, in our subjective and pro-mammalian opinion, are do distinct and unusual that we feel they ought to be placed in a group all of their own. If they were insects, or snails, or something like that, we'd probably feel differently. But they're mammals, like us, so we don't.

One such family is the walrus family, containing - you've guessed it - the walrus (Odobenus rosmarus). Walruses are pinnipeds, which is to say, they are related to seals and sea lions. Just by looking at them, we can tell that walruses can walk on all fours like sea lions and fur seals, but unlike "true" seals, yet lack the external ears that sea lions and fur seals have and true seals don't. When you get to the interior structure of the skeleton, and so on, there are a number of technical differences that tell us that, no, this isn't just our imagination, they really are a bit different from all the others. And, there's, you know... the tusks.

The Antlers of Early Deer

Dromomeryx, a palaeomerycid

Probably the most distinctive thing about deer is that they have antlers (and not horns). However, especially when we're looking at fossil species, it's important to remember that not all deer have antlers. Granted, the enormous majority do, and those that don't have lost them during their evolutionary history, rather than being holdovers from some ancient form that never had antlers in the first place. (This isn't true of musk deer, but that's partly why they aren't considered to be true members of the deer family).

And even that's assuming your fossil belongs to a male. (Or a female reindeer, oddly enough).

Antlers first appear on deer fossils in the early Miocene, on the general order of 20 million years ago. Still, in the grand scheme of the Age of Mammals, which has so far lasted 66 million years, that isn't all that long. It's a lot closer to us than it is to the dinosaurs, at any rate. So we ought to have a reasonable idea of what some of these first antlered forms look like.