Thylacosmilinae Riggs 1933 Thylacosmilidae is an extinct family of metatherian predators, related to the modern marsupials, which lived in South America between the Miocene and Pliocene epochs.

Later, with the discovery of fragmentary specimens of new sparassodonts related to Thylacosmilus from Miocene and Pliocene strata, Thylacosmilidae was promoted back to familial status.

[2][3] Also, additional materials of a small predatory sparassodont of Colombia have been found, which has certain features diagnostic of thylacosmilids, but much less specialized, as well as indeterminate remains in Uruguay and the Argentinean Patagonia, from the early Pliocene, has been tentatively assigned to family.

[1] Forasiepi and Carlini in 2010 unveiled a third genus and species, Patagosmilus goini, from the Collón Cura Formation of Argentina from the mid-Miocene, with characteristics intermediate between Anachlysictis and Thylacosmilus.

[5] Fossils of Thylacosmilus forelimbs, the only reported for this group, indicate that animals were not fast runners, and were in turn adapted to exert force in order to subdue their prey, helping with their semiopposable thumb.