USING THE FORCE: COMPARING PREDATION STRATEGIES AND EVOLUTIONARY PATTERNS OF THYLACOSMILUS ATROX AND OTHER SABER-TOOTHED FELIFORMS

Thylacosmilus atrox, a saber-toothed sparassodont marsupial from the Miocene and Pliocene of South America, is perhaps one of the most peculiar animals to have walked the Earth. This predator is unique in both the structure of its skull as well in its post-cranial morphology. Different saber-toothed animals may have had differing methods for taking down prey. For example, gracile feliforms would have likely chased their prey, whereas their more robust counterparts would have relied on an ambush approach. The elongated canines and robust forelimbs of Thylacosmilus suggest that it fell into the latter category, possibly hunting by wrapping one forelimb around the neck of its prey and using the other to push back the head of the unfortunate animal, exposing critical veins and allowing for a swift kill via a bite to the neck. We hypothesize that in an analysis comparing canine index to several forelimb measurements, T. atrox would plot near carnivores that are known to exhibit similar robustness in their forelimbs and that have also been interpreted as ambush predators, such as Barbourofelis and Smilodon. The specimens used for this study were measured from the Field Museum in Chicago, IL, which houses the holotype and paratype specimens of Thylacosmilus. The canine index, proximal paw width, and humeral epicondylar index of T. atrox were comparable to those of Smilodon and Barbourofelis, suggesting that all three taxa may have shared a similar hunting strategy. The humeral robustness index of T. atrox, however, was much higher than in any other saber-toothed predator, supporting the hypothesis that Thylacosmilus would have mostly likely been an ambush predator that subdued its prey with its forearms. Future research on sparassodont marsupials will indicate whether this behavior was widespread in South American predators or if it was unique to Thylacosmilus.