Pliocene (Pt 6): Attack of the Hyenas

Pachycrocuta brevirostris

Pliocene Europe was a continent as yet untouched by human hand - although, as I've noted, not of non-human primates. One might think that, in the absence of humans, sabretooth cats were probably the thing that other animals had to fear the most. There's probably a lot of truth in that, but they were far from the only carnivores in Europe at the time, and some of them were pretty fearsome.

On the other hand, there were also much smaller carnivores, too. At the bottom of the scale, weasels, badgers, otters, and martens already existed on the continent, and may have been quite common in the forests of the time. Foxes also survived the Zanclean Flood, and have continued living in Europe, right through the Ice Ages, up to the present day. In fact, Pliocene foxes would have looked remarkably similar to those of today, and are generally placed within the same genus, Vulpes.

Similarly, the largest carnivores of the European Pliocene would also have looked familiar. These were the bears, dominated by the gianr Agriotherium, which may have been slightly larger than a modern polar bear. Another woodland creature, it had perhaps been more common in the previous epoch, but survived throughout almost the whole of the Pliocene, dying out not long before the Ice Ages began in earnest.

Early on, however, it had been joined by the Auvergne bear (Ursus minimus). These are the earliest known members of the genus Ursus, and possibly the common ancestor of today's black, brown, and polar bears, and maybe even a few others besides. In fact, it looked, so far as we can tell from the skeleton, remarkably like a living black bear, and one can assume that it had a very similar lifestyle. As such, it seems to have suffered when the climate began to cool in the mid Pliocene, and, while it did not necessarily die out straight away, it was at least partially replaced by the larger Etruscan bear (Ursus etruscus). Although this has been disputed, this is often thought to be a descendant of the Auvergne species, forming a link between it and the brown and polar (but not black) bears, as well as being the ancestor of the large cave bears of the Pleistocene.

Worrying though an enraged bear might be, they are, on the whole, omnivorous creatures. The other major group of predators at the time, however, were a somewhat different matter. Hyenas had been in Europe for a long time when the Pliocene began, but very few made it past the changes following the Zanclean Flood. Instead, the Pliocene saw two entirely new hyenas reach the continent. Of the two, Pachycrocuta pyrenaica quite closely resembled the smaller hyenas of today - that is, the brown and striped hyenas, rather than the more famous spotted or "laughing" hyena. Like them, it probably lived in fairly open terrain, and did quite a lot of scavenging.

The other was the European running hyena (Chasmaporthetes lunensis), and it would have looked less familiar. A number of species of running hyena existed during the Pliocene, with one even reaching North America, and a new species from Tibet having been discovered just a few years ago. Indeed, running hyenas themselves were not new to the continent, with an earlier species having been discovered from fossil beds in Macedonia that pre-date the Zanclean Flood.

At any rate, one of the first things you would have noticed about a running hyena would be its relatively long legs. Taken together with a slimmer build, a longer, narrower, snout, and a back that - due to the length of the hind legs - sloped much less than those of the living species, you would have had an animal that, in general form, looked quite dog-like. It's the length of the legs that are the first clue to the animal's lifestyle, since they clearly suggest an animal that could run quite fast.

Besides "running hyena", an alternative common name is "hunting hyena", and this suggests the other key difference between this animal and the hyenas of today. While it was of similar size to modern spotted hyenas, the way that it acquired and ate its food seems to have been quite different. Like living hyenas, it had strong jaws, but analysis of the shape of the skull and the size and position of the muscle attachments suggests that these were primarily adapted for delivering a powerful bite with the canine teeth. Which may not sound particularly strange, and is, indeed how most carnivores work. But not hyenas, which, instead, focus much of their power on the teeth further back in the mouth.

They do that, of course, to crack open bone, something for which they specialised. Analysis of the patterns of wear on running hyena teeth support the obvious conclusion that this implies. Running hyenas probably could crack bone, but they were not as good at is as the living species, and were much likely to focus their efforts on stripping a carcass of all the meat that they could. Most likely, they lived in relatively open terrain, where their speed would allow them to chase down prey such as the local gazelles. Presumably, this meant that they would have competed with the European cheetahs of the day, likely being stronger, but not quite as fast.

One other difference has also been noted between running and modern hyenas. The latter have strong, powerful, females, that are very hard to tell part from the males even when you have a whole animal, let alone just a skeleton (looking at the obvious bit of the anatomy is surprisingly unhelpful). But analysis of running hyena skeletons has shown that one or the other sex had noticeably larger canine teeth than the other. There's no way to tell which one, of course, but that there's a discernible difference at all makes them unique among hyenas.

So was this fast-running, hypercarnivorous, potentially pack hunting animal the most frightening hyena of the European Pliocene? Well, it depends on what sort of things you find frightening, but quite possibly not. Because, in the mid Pliocene, as the climate dipped into the long autumn preceding the Ice Ages, the running hyena's unassuming counterpart, Pachycrocuta pyrenaica, evolved into P. perrieri. Which, okay, wasn't that much larger. Except that, as the Pliocene drew to a close, it, in turn, evolved into the giant hyena (Pachycrocuta brevirostris). Which was.

Just how big was a giant hyena? The skeletons we have are not complete, but the best estimate suggests something about the size of a lion. That's similar in shoulder height to the largest sabretooth cats of the day, but they were relatively slim, fast-moving animals, whereas this was a heavy, muscle-bound, creature. In fact, when you consider that bears such as Agriotherium were, at best, "mesocarnivores" (that is, omnivores that happen to prefer meat), you could well argue that, for a time at least, the giant hyena was the largest pure carnivore of its day.

Physically, it would have looked a lot like a spotted hyena. It had the same sloping back, the same long, muscular neck, and the same powerful jaws... it just happened to be much larger and about twice as heavy. So far as we know, it's the largest hyena ever to have lived, and it's pretty obvious that it was built for power, not speed. Furthermore, there is no doubt that its teeth and jaws, unlike those of the running hyenas, were ideal for cracking bones.

In fact, we have pretty evidence for what and how it ate, due to what appears to be a den of some of the creatures found in Spain. The site is littered with cracked bones, mostly of moderately sized hoofed animals. These remains show that giant hyenas cracked open the larger bones to get at the marrow, just as hyenas do today. On the other hand, given its size, it's unlikely that giant hyenas chased their prey even to the extent that spotted hyenas do today, and it may be that they were more purely devoted to scavenging.

Interestingly, the arrival of the giant hyena in Europe - it most likely originated in Asia - marked a major change in the mix of carnivores on the continent. It was certainly part of that, but the sudden turnover is instead named for another carnivore that reached Europe at the same time, and which had a longer lasting effect. This time, almost at the very end of the Pliocene, is known as the Wolf Event.

Although there had been foxes in Europe before, along with relatives of another small dog now found only in Asia, there had never been wolves. The wolf in question, the Etruscan wolf (Canis etruscus) isn't quite the modern species, being somewhat smaller. But it's likely its immediate ancestor, and it would become an important predator on the continent from this time forward.

Less long-lasting, although doubtless just as significant at the time, was the appearance at around the same time of the European jaguar (Panthera gombaszoegensis). Which may or may not have been an actual jaguar, but was certainly a close relative... and, besides, it's far easier to say "European jaguar" than "gombaszoegensis". Slightly larger than living jaguars, it almost certainly looked and acted in much the same way, until one too many Ice Ages brought its brief tenure to an end.

The Wolf Event more or less marks the end the of Pliocene in Europe, as the boundaries between the epochs are currently defined. There are, however, many Pliocene animals I have yet to describe, and it's time that I headed across the Atlantic to see what was going on in North America...

[Photo by "Tiberio", of a display at the Hungarian Natural History Museum. From Wikimedia Commons.]