Thylacoleonidae

Extinct family of marsupials
Automatic taxobox
| fossil range =
| image = Thylacoleo skeleton diagram. tiff
| image caption = Thylacoleo
| taxon = Thylacoleonidae
| authority = Gill, 1872 The best known is Thylacoleo carnifex, also called the marsupial lion. The clade ranged from the Late Oligocene to the Late Pleistocene, with some species the size of a possum, while members of Thylacoleo reached sizes comparable to living big cats.

A notable distinctive feature of thylacoleonids is their unusual blade like third premolars, which functioned as the carnassial teeth. Thylacoleonids varied widely in body size. One of the smallest thylacoleonids, the Early Miocene Microleo attenboroughi, is estimated to have had a body mass of , while the last species of the family, the Pleistocene Thylacoleo carnifex is suggested to have had a body mass of around , comparable to a big cat. Later members of the group saw progressive reduction in the number of teeth in the jaws. Earlier species of Thylacoleonidae like Lekaneleo roskellyae are suggested to have been omnivorous, while at least later species of Wakaleo and Thylacoleo are thought to have been hypercarnivores. though other authors have placed them at the base of Diprotodontia, outside of either Vombatiformes, Phalangeriformes or Macropodiformes. Thylacoleonids are thought to have evolved from herbivorous ancestors. The name is derived from the genus named by Richard Owen, Thylacoleo, which he recognised as a potent carnivore and described as marsupial version of the modern lions (Leo). A revision of the family was published in 2017, enabled by the discovery of a skull of an early species, named as Wakaleo schouteni, which allowed closer comparison with previously described species and the more complete fossil record of the lineages. The study by Anna Gillespie, Mike Archer and Suzanne Hand, revised the description of Wakaleo to include a new species and circumscribe taxa previously assigned to Priscileo.