Thylacoleonidae

Illustration of lower dentition reconstructed by Owen, 1877

A diprotodontian family allied to the Vombatiformes, mammals that radiated and diversified in the Oligocene to Miocene. The thylacoleonid genera exhibit specialised dentition that allowed them to kill prey larger than themselves.

The earliest descriptions of the most recent species recognise the secateur-like blades of the teeth as a powerful mammalian predator, a "marsupial lion," that were noted as missing in the Australian environment. The third premolars exhibit this blade-like development, becoming greatly enlarged in the Pleistocene species Thylacoleo carnifex, prompting the description by Owen as "…one of the fellest and most destructive of predatory beasts."[6] They are seen as presumably occupying a trophic level as peak predators in their local ecologies, some smaller and arboreal climbers while those terrestrial species are sizably comparable to large dog or a big cat.

The genera are associated with the late Oligocene and Miocene epochs. Microleo and Wakaleo have been located at the Lake Pitikanta fossil area in Central Australia and toward the northern coast at Riversleigh, below the gulf of Carpentaria, a rich source of fossil fauna. The most recent species, Thylacoleo carnifex, existed at least until the Pleistocene, the earliest known specimens of the family are dated to around twenty five million years ago.[7]

Thylacoleontidae is considered a member of Diprotodontia, though its precise position within that group is uncertain. They have often been considered a basal group (often the most basal group) within Vombatiformes, making their closest living relatives wombats and koalas,[8] though other authors have placed them at the base of Diprotodontia, outside of either Vombatiformes, Phalangeriformes or Macropodiformes.[9]

The family was described by Theodore Gill in a systematic revision of mammalian taxa published by the Smithsonian Institution in 1872.[1] 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.[6]