Saber-Toothed Marsupials?

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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