Thylacosmilus is an extinct genus of saber-toothed metatherian that inhabited South America from the Late Miocene to Pliocene epochs.
Though Thylacosmilus is one of several predatory mammal genera typically called “saber-toothed cats”, it was not a felid placentalian, but a sparassodont, a group closely related to marsupials, and only superficially resembled other saber-toothed mammals due to convergent evolution.
Thylacosmilus had large, saber-like canines. The roots of these canines grew throughout the animal’s life, growing in an arc up the maxilla and above the orbits. Its cervical vertebrae were very strong and to some extent resembled the vertebrae of Machairodontinae.
Body mass estimates of Thylacosmilus suggest this animal weighed between 80 to 120 kilograms (180 to 260 lb), and one estimate suggesting up to 150 kg (330 lb), about the same size as a modern jaguar. This would make it one of the largest known carnivorous metatherians.
Recent comparative biomechanical analysis have estimated the bite force of T. atrox starting at maximum gape at 38 newtons (8.5 lbf), much weaker than that of a leopard, suggesting its jaw muscles had an insignificant role in the dispatch of prey.