Thylacosmilus

Thylacosmilus is an extinct genus of saber-toothed metatherian mammals that inhabited South America from the Late Miocene to Pliocene epochs. Though Thylacosmilus looks similar to the "saber-toothed cats", it was not a felid, like the well-known American Smilodon, but a sparassodont, a group closely related to marsupials, and only superficially resembled other saber-toothed mammals due to convergent evolution, with the aforementioned Thylacosmilus being one of the last known sparassodonts. A 2005 study found that the bite forces of Thylacosmilus and Smilodon were low, which indicates that the killing techniques of saber-toothed animals differed from those of extant species. Remains of Thylacosmilus have been found primarily in Catamarca, Entre Ríos, and La Pampa Provinces in northern Argentina. Mass estimates of Thylacosmilus have varied depending on mass regressions, weighing , this makes Thylacosmilus one of the largest known metatherian predators.

== Taxonomy == alt=|left|thumb|Partially reconstructed holotype skull, [[Field Museum of Natural History]] In 1926, the Marshall Field Paleontological Expeditions collected mammal fossils from the Ituzaingó Formation of Corral Quemado, in Catamarca Province, northern Argentina. Three specimens were recognized as representing a new type of marsupial, related to the borhyaenids, and were reported to the Paleontological Society of America in 1928, though without being named. In 1933, the American paleontologist Elmer S. Riggs named and preliminarily described the new genus Thylacosmilus based on these specimens, while noting that a full description was being prepared and would be published at a later date. He named two new species in the genus, T. atrox and T. lentis. The generic name Thylacosmilus means "pouch knife", while the specific name atrox means "cruel". Riggs found the genus distinct enough to warrant a new subfamily within Borhyaenidae, Thylacosmilinae, and stated it was "one of the most unique flesh-eating mammals of all times".