Thylacosmilus was a saber-toothed marsupial predator that lived about 3 million years ago. It was not a relative of the true saber-tooth cats, but rather a prime example of convergent evolution. It was equipped with large teeth and powerful shoulders, both of which allowed it to dismantle its prey. Remains of the animal have been found in parts of South America. Thylacosmilus's sabre-teeth kept growing throughout its life, unlike the placental true saber-tooths. It also had sheath-like structures along the lower jaw designed to protect the sabre-teeth when they weren't in use.

It became extinct during the early Pleistocene as a result of the Great American Interchange, being outcompeted by true saber-tooth cats such as Smilodon.

Prehistoric marsupials | Pliocene mammals | Pleistocene mammals | Pleistocene extinctions | Thylacosmilus