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A Smilodon fends off the vulture-like Teratornis at what would later be called the Rancho La Brea tar pits, situated in Los Angeles, California (Painting by Charles R. Knight)

Lately this blog has been fixated on magnificent saber-toothed mammals.  We have featured the extinct saber-toothed whale, a saber-toothed marsupial predator, the little saber-toothed deer, and even the familiar walrus (in reality, a giant saber-toothed seal), but we realize that everyone has really been looking forward to the most famous saber-toothed animal of them all, Smilodon, the saber toothed cat.  Smilodon was actually a genus of several large cats, the biggest of which, Smilodon populator, weighed 360 to 470 kg (790 to 1,000 lb) and was larger than modern tigers or lions. In fact Smilodon species are sometimes known as “saber toothed tigers” or “saber toothed lions,” however taxonomists tell us such names are off the mark since the Smilodons belonged to the extinct Machairodontinae genus of felines rather than the familiar Panthera genus of big cats so familiar today.

About two and a half million years ago, Smilodon evolved in North America from an earlier genus of saber toothed cat Megantereon (there were a lot of other earlier genera of saber-toothed cats, not to mention even more genera of saber toothed carnivores which were not exactly felines—the whole story is complicated).  During the Great American Interchange with South America the big predators invaded South America at the same time armadillos were making their way up into North America.  Yikes, that’s a pretty lopsided exchange.

In addition to long razor sharp teeth, Smilodons possessed immense neck and forelimb muscles. Using the muscles of their front torso they would pull down and pin the great grazing metafauna of the American plains.  Prey animals almost certainly included bison, tapirs, deer, American camels, and ground sloths. Additionally Smilodons might have opportunistically killed juvenile mastodons and mammoths. To dispatch such large prey Smilodons employed their fearsome canine teeth with which they bit through the prone creatures’ necks.

Smilodon fatalis (reconstruction/specimen at the Page Museum)

Paleontologists have collected a great deal of fossil evidence concerning Smilodons, which suggest that the big cats were sophisticates social predators like today’s lions or wolves.  The number and nature of saber-toothed cat fossils recovered from tar pits suggests that Smilodon prides would converge together on prey animals caught in the petrochemical ooze–only to become trapped themselves.  Also some fossilized smilodons have shown evidence of badly broken bones healing—a rarity in carnivores which is generally only possible for pack/pride animals which can (sometimes) rely on a support network.

Thanks to their size, ferocious appearance, and highly characteristic teeth, Smilodons have a special place in human culture to the extent that few other extinct animals do.  The Flintstones had a pet smilodon named “Baby Puss” which evicted Fred from his house in the title sequence and the moral struggles of Diego the saber tooth constituted the moral hook of “Ice Age” a cartoon movie. Ironically for all of our apparent fondness for the great cats, it seems that human migration into the Americas may have been the downfall of the great cats (which vanished 10,000 years ago) but whether their extinction was the result of humans overhunting their prey, shifting climate, or some other factor remains an open question.

Smilodon by Knight

Thylacosmilus digital illustration

I have always been fascinated by saber-toothed animals.  Only a few saber toothed creatures remain in today’s world (like the estimable walruses and a few tiny saber-toothed deer) but in fearsome ages past, the design was widespread.  Most readers are probably familiar with the smilodons, the magnificent saber-toothed cats which hunted the megafauna of Pleistocene North and South America, however the story of the saber-toothed cats intersects the story of another giant saber-toothed predator which was nearly as fearsome and even stranger. Thylacosmilus was a genus of saber toothed marsupial predators which ruled South America during the Miocene and Pliocene.  Like the smilodons, Thylacosmilidae were large, agile predators which used their long fangs to slash the throats of huge prey.  Unlike Smilodons, Thylacosmilidae were marsupials which gave birth to a tiny helpless larva which they then nurtured in a pouch.

Thylacosmilidae (artist unknown)

The prominent teeth of Thylacosmilus were a result of convergent evolution and the creatures did not share any direct ancestors with cats since the divergence of placental and marsupial mammals (deep in the depths of the Mesozoic).  Thylacosmilus’ teeth were also different in that they continuously grew throughout the animal’s life.  The teeth were probably worn down as the predators gnawed on bones.  Additionally Thylacosmilidae possessed scabbard-like bone flanges built into its lower jaw to protect its teeth (a feature missing entirely from Smilodons).  Who knows what sort of noises Thylacosmilidae made with these peculiarly shaped mouths? For millions of years Thylacosmilidae lorded over the strange mammals of South America.  The glyptodonts (and possibly other armadillos) developed their armor to ward off the mighty beasts.  However the fickle play of tectonics undid the mighty killers.

Thylacosmilidae and Smilodons were not closely related (click on this picture to visit "Understanding Evolution" an excellent site where I found this helpful image)

In the beginning of the Pliocene, a land bridge joined North America and South America and suddenly the true cats arrived on what had been an island continent.  As the climate dried out, Smilodons competed directly with Thylacosmilidae. Strange new herbivores appeared to displace the old prey animals.  The Great American Interchange of long sundered mammalian lineages proved too much for the saber toothed marsupials.  Thylacosmilidae were giant and fierce but they were no match for invasive cats.

Thylacosmilus atrox (digital art by viergacht)

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