Oligocene (Pt 12): Reign of the Hyena-Cats

Apterodon

In most parts of the world today, all large, carnivorous, land-dwelling mammals are members of the order called, appropriately enough, the Carnivora. This is the group to which cats, dogs, and bears belong, along with many other animals from weasels to seals. If we go back far enough in time, we find that this group originated on the northern continents and was unable to reach the then-isolated southern ones until much later. During the Oligocene, therefore, there were no carnivorans in Africa.

Which isn't to say that there were no carnivorous mammals at all; absent some non-mammalian predator to out-compete them, it's just too useful a niche for nothing to evolve to make use of it. But those mammals were not close relatives of the lions and hyenas that live there today, belonging to different branches of the mammalian family tree.

Most of those branches have since vanished from the world, but that's less true for the small carnivorous mammals that dine on insects and worms rather than vertebrates. Qatranilestes lived in Egypt around 30 million years ago. We only have a fragment of one jaw, so it's hard to say how big the animal was, but it probably wasn't much larger than a mouse. Descended from very ancient African stock, so far as we can tell from such limited remains, it was related to the tenrecs that today inhabit the central parts of the continent and the island of Madagascar. 

The tenrec family that exists now did not arise, so far as we know, until the early Miocene, but with nothing more than a couple of sharp, biting, teeth to look at, we can't say how close this animal was to its living relatives. But, much like them, it was probably a fierce shrew-like creature. If it left any descendants, they moved south, since nothing similar is known from northern Africa from then on.

Much of the problem here comes from the fact that Egypt has by far the best Oligocene-age deposits in Africa - or at least, the most thoroughly studied. What else was going on on the continent at the time is relatively obscure. The ptolemaiids are a case in point. As their name might imply, they were first discovered, in the form of the eponymous Ptolemaia, from Egyptian deposits. With only fragmentary remains to go on, it was initially thought that they might be primitive primates, but once we got a more complete sample, including a long snout with large and sharp canine teeth, it became obvious that they were some kind of carnivore.

But quite what kind of carnivore was still not obvious. Ptolemaia looked, in some respects, like a shrew, but it was quite a lot larger. By the late 1980s, we knew of two other genera of ptolemaiid, all from Egypt, with the largest, Cleopatrodon, being about the size of a badger, albeit with a more shrew-like body form. Even then, quite where they fit within the mammalian family tree remained obscure, with some of the more outlandish theories even relating them to bats. The problem was their unusual teeth indicated that they were clearly something odd, but most of their other features were simply primitive - the sort of thing that could be inherited from a very early ancestor and could therefore be shared with almost anything.

In 1995, it was finally decided to sidestep the problem by conceding that they were strange enough to be placed in their own group and they have remained there ever since. In the larger scheme of things, there are anatomical indications that they descend from an ancient African group, rather than anything originating on the northern continents, although, admittedly, this is hardly surprising. It wasn't until 2015 that we found ptolemaiid remains from somewhere other than Egypt, and that Kenyan fossil supported what had then become the leading theory that the animals' closest living relative is the aardvark. Not a very close relative, to be sure, but closer than anything else. (By this point, incidentally, a Miocene animal had been identified as a later member of the group - it was about the size of a wolf, so clearly they became more impressive over time).

Although there seems to be general agreement that the early ptolemaiids probably ate flesh of some kind, the details of their diet remain uncertain, and even that much isn't absolutely clear. Their teeth were sharp, but they were oddly shaped with wear patterns that suggest they might have often bitten down on something hard... snails and shellfish seem obvious candidates, but we're just guessing by this point.

There were, however, larger predators, too. These belonged to a group called the hyainailouirids, a term that literally translates as "hyena-cats". Hyena-cats were, of course, neither hyenas nor cats, although they did share some features in common with both. They belonged to a wider group of animals that was, in fact, quite closely related to the true carnivorans of the north, but that had split off from their common ancestor early on. In the subsequent, Miocene, epoch, these hyaenodonts would become widespread, with some reaching at least the size of a lion, but we have relatively few fossils of them from the Oligocene to see how they evolved through this transition.

Exceptions from the early Oligocene include Falcatodon and Sectisodon, smaller relatives of hyena-cats that would later spread into Asia and Europe before eventually dying out, perhaps out-competed by true carnivores. These are mostly known from Egypt, although we do have an example from Uganda, and it's likely that they, or their close relatives, were the dominant mammalian apex predators across much of Africa. Towards the end of the epoch, we have Pakakali, described as being probably the size of a bobcat.  The shape of its teeth suggest a somewhat omnivorous diet, albeit one focussed primarily on small vertebrate prey - again, more like a bobcat than, say, a cougar.

While we may not know as much about these animals as we do about their counterparts on other continents, or from other epochs, they were already diverse by the Oligocene. While most were typical land-dwelling predators, Apterodon, known from Egypt and Libya, and which later reached Europe, had limbs that suggest it would have been relatively slow-moving and unsuited for climbing. Or at least, slow-moving on land, since they do seem well adapted for swimming and probably also for digging. This suggests an animal that lived somewhat like an otter, and that may have lived along a substantial stretch of the African coastline.

Although the fossil history is patchy, it is enough to suggest that the hyena-cats, and possibly the larger group to which they belonged, originated in Africa, rather than descending from some even earlier group elsewhere. It is difficult to know for sure, however, and the broader group is old enough that it could have first appeared when the continents were in a different arrangement even than they were in the Oligocene. 

Still, if they are difficult to place, the small carnivorous mammal Africtis is even more so. Known only from Oligocene Libya, analysis suggests that it may have been more closely related to the true carnivorans than to the hyena-cats elsewhere on the continent, although it almost certainly does not descend from the last common ancestor of those alive today. If so, it's unclear quite what it was doing in Africa so early, since it would have to have somehow rafted across from Eurasia before the continents joined up - an unusual, but not impossible, feat.

With that, admittedly incomplete and somewhat frustrating picture of African wildlife in the Oligocene, it is time to leave the continent and head west towards one of the other island continents then occupying the Southern Hemisphere...

[Picture by Henry Fairfield Osborn, in the public domain.]