New jaws and teeth referable to the rare thylacoleonid marsupial Wakaleo alcootaensis are figured and described. The species is the geologically youngest known member of the genus and is only known from the late Miocene Alcoota Local Fauna of the Northern Territory, Australia. A revised diagnosis of the species is presented which is found to be morphologically distinct from its congeners. W. alcootaensis can be distinguished from other species of Wakaleo by its greater size, deeply recessed masseteric fossa, more steeply angled I 1 , loss of P 2 , greater P 3 to M 1 ratio and loss of M 3 . Several characters of W. alcootaensis , including the increase in size, steeply angled I 1 , increase of the relative size of P 3 , and reduction of the molar row are present in at least some species of Thylacoleo . Phylogenetic analysis suggests that these character states are convergences and that there was parallel evolution in these two thylacoleonid lineages.