Thylacosmilus atrox is an extinct species of saber-toothed metatherians that inhabited South America from the late Miocene to Piacenzian epochs. Remains of this animal have been found primarily in Catamarca, Entre Ríos, and La Pampa Provinces in northern Argentina. Though Thylacosmilus is one of several predatory mammal genera typically called "saber-toothed cats", it was not a felid but a sparassodont, a group closely related to marsupials, and only superficially resembled other saber-toothed mammals due to convergent evolution.