Miocene (Pt 5): Hyenas in the Treetops

The first hyenas somewhat resembled this African civet

When we think of prehistoric carnivorous mammals, the first image that probably pops to most people's minds is that of sabretooth cats. It will therefore be no surprise that, were we to visit Middle Miocene Europe, one of the most widespread carnivores that we would find would be a moderately-sized cat-like animal with enlarged, serrated canine teeth in its upper jaw. What might be a little more surprising is that it wouldn't actually be a sabretooth cat.

The animal was called Prosansanosmilus, and it is known to have lived at least across what is now western Europe, from Spain to Germany. It, or its immediate ancestor, had probably first evolved in northern Africa, and arrived in Europe not long after that continent had collided with its northern neighbour - one of many animals to cross over as part of the so-called "Proboscidean Event". In life, it would surely have looked much like a cat, albeit with shorter legs and flatter paws less suited to pouncing and other rapid movement. But, in fact, it was not a cat, but a member of a family that, like the bear-dogs, no longer exists; that of the barbourofelids, or "false sabretooths".

The exact relationship between barbourofelids and cats is something that has undergone a fair amount of revision in the last 40 years or so. When Prosansanosmilus was first discovered and named, in 1980, it was considered to be a nimravid, a member of a group of diverse animals found across much of the globe, and that bore a striking resemblance to modern cats. Indeed, so similar were they, that, in 1988, a new analysis placed Prosansanosmilus as a true cat. That didn't last for long, and it was soon moved back again, but the differences between it and other nimravids (primarily with regard to the shape of the skull, and details of the teeth) were hard to ignore, and it was punted over to a separate subfamily.

There it would have stayed had it not become clear, in 2004, that it and its relatives were, if not literally cats, at least rather more closely related to them than the nimravids were. And so, the barbourofelids became a family in their own right, a shorter-lived, but equally widespread, counterpart to the true nimravids. This is particularly interesting since one of the reasons that the animals had been placed together previously was that they all evolved elongated sabre-teeth. Which means that sabre-teeth must have evolved at least three times among the cat-like animals - in the nimravids, the barbourofelids, and, of course, the true cats. It's clearly a very useful trait for animals that hunt in an at least broadly feline manner, and, if anything, it's a wonder that there aren't some still around now.

The current picture is that, while true nimravids had once lived in Europe, they died out there some time before the dawn of the Miocene, with Prosansanosmilus taking their place around 17 million years ago. During the interim, there don't seem to have been any particularly large cat-like animals on the continent, but, while they might not have been quite so obvious, there were some smaller ones, and these, as it happens, really were cats.

Pseudaelurus, already living in Europe around the dawn of the Miocene, was, at first, not much different in size from a modern house-cat, but had shorter limbs that were probably more suited to climbing. I say "at first" because we know of at least three species belonging to this genus and living in Miocene Europe. While the small one (P. turnauensis) came first, it was soon joined by two other, larger, species, but actually outlived them, surviving almost to the end of the epoch, surviving some significant changes in the climate to do so.

Of the other two species, one, P. lorteti, was about the size of a lynx or bobcat, but far more adapted to living, and perhaps sometimes even hunting, in the branches of trees. The third species, P. quadridentatus, was larger still - at about the size of a smallish female cougar, it's likely to have been much less arboreal. While it may not have lasted as long as its older cousin, it was even more widespread, being found as far east as Mongolia. It has another interesting trait, too, in that it is the first true cat we know of to have enlarged upper canine teeth.

It's not quite a sabretooth, but it has been proposed as a possible ancestor for the group that later became the true sabretooths. This may well mean that it isn't as close a relative to the other two species (let alone to the North American forms traditionally given the same name) as was previously thought. If so, since it was described first, it gets to keep the name, and the other two species would be given the alternative name of Styriofelis. Either way, between them, the three species are too primitive in form, and lived too early, to be assigned to any of the three commonly agreed subfamilies of cats - if P. quadridentatus really is the ancestor of the sabretooths, Styriofelis might well include the ancestor of the other two subfamilies, and hence, of all cats alive today.

By the Middle Miocene, around 15 million years ago, these cats and false sabretooths were joined by the first hyenas. It's not completely clear where hyenas first appeared; the oldest fossils are found in eastern Europe and the Middle East, but that's so close to the connection with Africa (which would have existed by that time) that it's possible they had recently crossed over from a nearby part of the southern continent. At any rate these very early hyenas, notably Protictitherium, were really quite unlike the animals we know today.

In fact, Protictitherium was about the size of a beagle or spaniel, and had retractable claws and a body suited for clambering about in trees. Overall, it looked much more like a cat than a dog, and it probably fed on small mammals, birds, and insects that it caught in the woodland. Somewhat later, it was joined by Plioviverrops, a similar-looking animal that had adapted slightly more to living on the ground, and with weaker teeth that suggest insects formed the largest part of its generally omnivorous diet. So unlike modern hyenas were these animals, that some scientists prefer to place them in their own, closely related group, but the more general consensus at present is that they're just really, really, primitive members of their family.

These early, omnivorous and partly tree-dwelling hyenas, survived for a long time in Greece, and especially Turkey. Towards the end of the Middle Miocene, they were joined by a third form, Thalissictis, which first appeared in western Europe, before spreading east, and eventually reaching northern Africa. This was closer in size to a typical collie or setter, and seems to have been adapted for hunting in open woodland. Although probably not a pure carnivore, its teeth were more robust than the earlier species, and it likely ate a lot more meat than they did; it's the first step we know of down the long route to the vicious scavenging habits of most modern hyenas.

Living alongside these omnivorous proto-hyenas, however, were some genuine scavengers, and these were a much larger animal. Percrocuta first appeared in western Asia, but spread slowly across Europe, eventually reaching as far as France. It was slightly larger than the largest modern hyenas, and had heavy, meat-cutting teeth and other hyena-like adaptations. While they probably weren't very good at cracking open bone, they would likely have been effective enough at stripping down the rest of a carcass. For a long time, they were thought to be early examples of scavenging hyenas, but, on the basis of some differences in the development of their milk teeth, it is now thought that they belong to yet another extinct family of carnivores, albeit one closely related to the true hyenas.

Before we leave the carnivores of the first half of Miocene Europe, however, there is one other scavenging animal that I should mention. Hyainailouros was a large animal, about the size of a male lion, with large teeth, and limbs that, while they may have been good enough for running, don't seem to be well adapted for striking at and taking down prey. With long jaws and a low forehead, it would have looked slightly odd to modern eyes, and, indeed, it was not at all closely related to either dogs or cats. Instead it was one of the last of the creodonts, a much older lineage of animals that had long been extinct in Europe, but had held on in Africa, slowly becoming large enough that, when the opportunity arose to re-enter Europe, it succeeded where they had ultimately failed. Its remains are mostly known from France, but have also been found in Spain, Portugal, Germany, and Switzerland; a closely related species in Asia reached at least as far as Pakistan.

This time of false sabretooths, small cats, tree-climbing omnivorous hyenas, and giant scavengers came to an end when the climate took a sudden turn for the worse around 14 million years ago. This heralded a significant change in the local wildlife, of which perhaps the most significant for many of the animals I've described here was the arrival of the first true sabretooth cats. Before we look at them, though, we must turn to see what else changed in Europe around this time, and what it was that the first true sabretooths would have been eating...

[Illustration attributed to Richard Lydekker (d. 1915), in the public domain.]