Sunday, 31 May 2015

Pliocene (Pt 5): The Last Sabretooths in Europe

Apologies for the absence of a post last week. This was due to personal circumstances that meant I just couldn't bring myself to write. Normal service has now been resumed.

Six million years ago, there were many different kinds of sabretooth cat in Europe. That, however, all came to an end with the Zanclean Flood and the dawn of the Pliocene epoch. It's not that they literally drowned in the flood, of course - almost by definition, most of the parts of Europe we know today were above where the flood waters stopped. But Europe changed in the aftermath of the flood, seeing, over an admittedly long period of time to human eyes, a change in the nature of the herbivores that lived there. And, when the herbivores change, so do the animals that have to eat them.

Most of the European sabretooths died out in the very earliest part of the Pliocene. The one exception was the "terror cat" Dinofelis, which became perhaps the dominant large predator in Europe for the next million years or so. However, once the climate took a turn for the worse, and the long prelude to the Ice Ages began around three million years ago, Dinofelis followed its relatives into extinction.

This did not leave Europe without sizeable cats, however. With the decline of the sabretooths, some more modern-looking cats began to take over. At around the same time that Dinofelis went extinct, for instance, the Issoire lynx (Lynx issiodorensis) entered the continent, heaving headed north from Africa. This is the ancestor of all lynxes alive today, with its descendants having later crossed to America to give rise to both the Canadian species and the modern bobcat. (The caracal "lynx" of Africa and the Middle East is an exception here, not being a real lynx at all, but just having ears that look kind of similar).

The Issoire lynx was more heavily built than any of the modern species, however, although, if it didn't have the thick fur of the Canada lynx (and it probably didn't) that wouldn't necessarily have been very obvious. Its limbs were shorter, and its head larger and longer than modern lynxes, so it probably looked a bit like a short-tailed puma. Together with the fact that it had stronger jaw muscles, this may well indicate that it took larger prey than modern lynxes and bobcats do, and it probably wasn't just rabbits that had to fear its presence.

Towards the very end of the Pliocene, it was joined by the European cheetah (Acinonyx pardinensis), a species so closely related to the living sort that it may really just be a subspecies. Given this similarity, it is surprising just how far through the later Pleistocene epoch this would go on to survive, although it did die out before the worst of the Ice Ages. It is sometimes said to have been the "size of a lion", and it certainly was larger than any modern cheetah. However, while its shoulder height was, indeed, about the same as that of a lion, it was nonetheless cheetah-shaped, making it considerably lighter and less powerful.

Having longer limbs, it's just about possible that it was faster than modern cheetahs, although the fact that it would also have weighed more rather counts against that, and it's hard to see what it would have needed such speed for. As for what it ate, there were antelopes in Europe at the time, so they're a likely candidate.

However, these were not the only large cats in Pliocene Europe, for Dinofelis did not mark the end of the local sabretooth lineage. As the climate cooled, and it died off, two new sabretooth cats arrived to take its place.

Megantereon cultridens was, in fact, the first sabretooth fossil to be formally described, back in 1824, 18 years before the more famous Smilodon. At the time, it was thought to be a bear (in Cuvier's defence, he was only looking at a few teeth), and it took another four years before anyone realised it was really a cat.

The exact number of species within Megantereon is a matter of some dispute; at least eight have been named, but it's unclear how many of them are really distinct. It has been proposed, for example, that some of the variation between them may be down to some fossils belonging to males and others to females. Some authors have argued that M. cultridens may be the only species, although, if so, it's very widespread. On the other hand, it's actually pretty hard to tell lions and tigers apart from the skeletons alone, so such debate over fossil cats is, perhaps, unsurprising. If I were to guess, I'd say three species - one each in Eurasia, Africa, and North America - is a plausible number.

Megantereon probably first appeared in Africa, and then spread north to occupy almost the whole of the Northern Hemisphere. Once in North America, it likely became the immediate ancestor of Smilodon, although claims that it first appeared on that continent (rather than Africa) seem less popular these days. In Europe, it seems to have lived mainly in the south, and did not, for example, reach Britain that we know of. It does not seem have been terribly common anywhere, although that is perhaps unsurprising for a large cat that presumably required rather a lot of food to feed itself, and must have competed with others of its kind for resources.

The best known and most complete specimen was discovered in the Auvergne of France, and shows an animal about the size of a large jaguar, with muscular forelimbs and large claws. All of this fits with what we know of its more spectacular Pleistocene descendant, Smilodon - it probably held prey down with its forelimbs and body weight while it ripped open their throats with its sabre teeth.

Its build was not quite as extreme as in Smilodon, and, while the latter was a muscular killing machine, Megantereon was likely more graceful, moving swiftly after its prey, and probably agile enough to climb trees as leopards do. The sabre teeth, however, were nearly as large, and, unlike those in the later species, fitted against a pair of short bony flanges extending down from the lower jaw. It had the typical short tail of sabretooth cats, and a long neck, which may have helped improve their aim when biting. It would have fed on larger prey than the European cheetah, almost certainly including large deer, and probably also including the pony-sized horses of the day, and maybe even baby rhinos.

Megantereon was not, however, the largest cat in Europe at the time. That honour goes to the scimitar-toothed cat Homotherium latidens, an animal that evidently lived alongside its smaller cousin, since fossils of both have been found at the same sites. Having said that, Homotherium also lived further north, probably as far as Britain, and certainly into Germany. It survived for longer, too, being the last sabretooth to die out in Europe, in the early Pleistocene, and surviving alongside Smilodon in North America until almost the end of the Ice Ages. At the other end of the scale, we don't know where it first came from; equally old fossils are known from Africa and Asia, both dating to around 4 million years ago.

Considering that they are both sabretooths, the two animals were, however, different in a number of ways. For a start, the sabre teeth of Homotherium, while similar in size to Megantereon's, were serrated along the rear edge, like a steak knife, presumably helping them rip into tough flesh. As I noted above, they were also larger animals, similar in size to a lion, but much more slender, and with smaller, less retractable claws that suggest they may have been good at running. Their neck was nearly as long as in Meganteron (and presumably, for the same reason), and they, too, had a short tail.

Another feature that may suggest sprinting ability is that the forelimbs were particularly long, giving the animal a sloping back similar to, if less extreme than, that of a hyena. Presumably, Homotherium loped along the ground in pursuit of its prey, a hunting style that would suit a pack-living animal. That latter part, of course, is purely speculation, but, either way, such pursuit-based hunting is not all typical of the ambush-and-pounce tactics of most sabretooths (or cats in general, cheetahs aside), and would have given the animal an advantage in open, grassy, terrain.

Homotherium would have been able to take down moderately large prey, and, if it really did live in packs (which, again, we don't know), its victims might have been even larger than we think. But we do know that they ate baby mammoths, since such remains have been found in a cave in Texas, and if mother mammoths protected their children anything like modern elephants do, that can't have been at all easy.

While sabretooths survived much longer in North America, in Europe, Homotherium was eventually driven to extinction in the early Pleistocene, probably due to the arrival of cave lions, which were even larger than they were. The two did live alongside one another for a while, presumably by sticking to different habitats, but, in the end, the cave lions won out.

But then, sabretooth cats had never been alone. There were other predators in Europe at the time, and it is to them that I will turn in Part 6.

[Picture by Sergio de la Rosa Martinez, from Wikimedia Commons]

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