Thylacosmilus was a genus of sabre-toothed metatherian predators, that first appeared during the Miocene. Remains of the animals have been found in parts of South America, primarily Argentina. Though Thylacosmilus is one of several predatory mammals typically called “sabre-toothed cats”, it was not a felid but a sparasoodont, a group closely related to marsupials. It resembled other sabre-toothed mammals due to convergent evolution.
Thylacosmilus had long, sabre-like upper canines and short, blunt, peg-like lower canines. The incisors were missing altogether and the other teeth were severely reduced. Estimated to weigh around 150 kilograms, it was the largest carnivorous metatherian, along with the marsupial lion.
Thylacosmilus went extinct during the Pilocene, a timeframe closely corresponding to the arrival of the sabre-toothed cat Smilodon from North America.