Monthly Archives: May 2013
A former “pet theory” about the sabertooths was that they were specialized for hunting giant, slow and thick-skinned prey, and that when those herbivore behemoths went extinct, the sabertooths found themselves unable to capture the faster, smaller prey such as horses and antelopes. Then sabertooths went extinct, while the modern cats triumphed, because the latter were fast and smart and so they could chase and even use group tactics to catch the fast prey animals.
So the thory went, but it was largely based on the observation of the fossils of Smilodon, which is the heaviest, most robust of the sabertooth cats. Even for Smilodon the theory is certainly wrong, but the fact is that also in the Pleistocene there lived another kind of sabertooth: Homotherium, the so-called scimitar-tooth cat. In the Old World, Homotherium coexisted with the lion for many thousands of years, and when one compares the anatomical structure of these two top predators there are quite a few surprises to be found:
Homotherium was not a slower or heavier animal than a lion. In fact it was on average a lighter animal, especially when compared with the Pleistocene lions of Europe that were larger than their modern counterparts. You can see that difference at a glance looking at the drawing below, where both animals are shown to the same scale: the Pleistocene lion is shown at left (life outline on top, skeleton at bottom) and Homotherium at right. Homotherium had comparatively long forelimbs, and its wrist was narrower, better adapted to running and less adequate for handling prey.
The claws of Homotherium were smaller and less retractable than those of the lion, except for the large dew-claw, as happens with the living cheetah, again adaptations for sustained running rather than grappling heavy prey.
The teeth of Homotherium were precision tools perfect for cutting the throats of large prey animals, but given that each individual cat was more of a runner and less of a wrestler than an individual lion, there is one clear implication: in order to hunt the animals that its teeth were adapted to kill, a cat with the limb anatomy of Homotherium almost inevitably had to hunt in groups.
The size of the upper canines limits the diameter of the necks of prey animals that Homotherium could bite, so it is clear that it would not hunt adults of giant species such as proboscideans, rather it would target animals within the high part of the size range of the prey taken by lions, that is: large bovines, horses and the young of the giant species.
So we see a lot of overlapping and potential competition with lions, more so than the old cliché of the sabertooths as slow brutes would have us think. So now new questions arise: how did those animals avoid the worst of competition for so many thousands of years? And how did the lion manage to survive the crises of the Pleistocene that killed off the sabertooths and so many other species of large mammals?
Those are good questions indeed… and evidence points to some rather surprising answers. That evidence is discussed at some length in the upcoming book “Sabertooth”. Stay tuned!
There is a popular misconception that sees the sabertooths as older, primitive relatives of our modern big cats -even as their ancestors. But the fact is that both lineages share a common ancestor that lived more than 20 million years ago, and since then they have evolved independently. Actually, the feline cats have changed much less in the course of all those millions of years, and they resemble that common ancestor more closely, so, ironically, it is the sabertooths who became more specialized, and our felines that remained more “primitive”.
One striking snapshot of the evolution of the two cat lineages (sabertooths and felines) is provided by the exceptional sites of Cerro Batallones in Madrid. This complex of fossil sites of late Miocene age (about 9 million years ago) has yielded an amazing treasure of fossils of carnivores, including the best sample in the world of 2 species of sabertooth cat, Machairodus aphanistus and Promegantereon ogygia. Machairodus was the first sabertoothed felid to reach the size of a lion, and it had a range of prey animals to choose from, including horses, antelopes, jiraffids, rhinoceroses and maybe even young mastodons. Such variety of herbivores would offer suitable prey for a modern big cat such as a lion or tiger, and one wonders: where were the ancestors of our big cats in the late Miocene? Well, the answer is they were right there, sharing the same ecosystems, but they certainly were not competing with the sabertooth for prey… because none of those felines was larger than a lynx!
Yes, the feline cats lived in the shadow of their sabertoothed cousins for many millions of years just like mammals lived in the shadow of the dinosaurs. And we are finding there was more variety of them than we used to think. For years we assumed that all the fossils of small cats from Batallones belonged to Felis attica, a serval-sized species commonly found in the late Miocene of Eurasia. But when a team of paleontologists led by Manuel Salesa from the MNCN in Madrid set out to study those fossils in more depth, we found some surprises.
As it turned out, most of the small cat fossils from Batallones belonged to a different genus and species (a new one, by the way) , Styriofelis vallesiensis, which differs from Felis attica in retaining more teeth (a primitive feature) and being slightly smaller, and which would have been rather similar to a modern wildcat. During the same study, we took a close look at fossils of the common species “Felis attica” and we found that it differed so much from modern species of the genus Felis that it was impossible to keep it in the same genus, so we created the new genus Pristifelis for those Miocene cats. Now the interesting thing is that several postcranial fossils from Batallones are slightly larger than those of Styryofelis vallesiensis and indicate the simultaneous presence of Pristifelis at the site. This combination reminds me of the situation in the modern African savannah, where the african wild cat and the serval cat share the same ecosystem with the cheetah, the leopard and the lion. In the case of Batallones, the big cat niches were firmly held by the sabertoothed species, and the felines were restricted to the role of rodent and bird hunters, a situation that would remain that way for millions of years until the late Pliocene. By that time, some felines evolved into full jaguar-sized beasts and for the first time they challenged the sabertooth supremacy. What led to such dramatic developments? Well, that is a different story…
Here is an illustration showing the small feline cat from Batallones, Styriofelis vallesiensis, to the same scale with the sabertooth Machairodus aphanistus. Even I was surprised by the size contrast when I put these two together!
And for those more technically-minded here is a link to read a PDF of our scientific paper about the Batallones small cats:
Sabertooth predators evolved at least 5 times independently among mammals. Among them, the first group to attain all the extreme adaptations that we associate with the sabertooth “model” were the nimravids, a family of true carnivorans that thrived in the Eocene and Oligocene periods. Almost 30 million years ago (when the ancestors of more familiar sabertooths like Smilodon were only ocelot-like creatures chasing smallish prey in the forests of the Old World), the nimravid lineage of Eusmilus had already acquired all the “sabertooth” adaptations to the limit or nearly so. With the body size of a large leopard, the american species Eusmilus sicarius was a giant among the carnivores of its time. Of course it had enormous saber-like canines, but it also had other attributes that we see in other specialized sabertoothed predators: a huge downward projection on its chin; large incisors arranged in an arch well ahead of the canines; an enormous mastoid process for the attachment of powerful neck muscles that aided the animal to sink its sabers into the flesh of prey; and quite a few other subtle features. Other families of mammals would make their own “experiments” with the sabertooth adaptations, but this nimravid was the first to achieve this level of sophistication. And yet the nimravids disappeared without descendance near the end of the Oligocene. The cause of that extinction is a great mistery, but certainly it is not a unique episode. Sabertooth predators have evolved time and again with enormous success, becoming the top predators in several continents, and each time they have been wiped off the face of the Earth. In a way, they died of success, something that should give us humans food for thought. But that is a different story…
And here is a life reconstruction of Eusmilus sicarius, the apex of sabertooth ev0lution in the Oligocene of North America. The animal was about the size of a large leopard. Some paleontologists think this species does not belong in the genus Eusmilus but rather in Hoplophoneus, but while we await for this matter to settle I will use the traditional name here.