Two new marsupial lion taxa (Marsupialia, Thylacoleonidae) from the early and Middle Miocene of Australia

Five species of marsupial lions (Thylacoleonidae) have been documented from the Oligo-Miocene freshwater limestone deposits of the Riversleigh World Heritage Area in northwestern Queensland, significantly altering understanding of the evolution of this extinct family. This paper presents a further two new thylacoleonid taxa from this fossil-rich region: Lekaneleo myersi sp. nov., from middle Miocene deposits, and Enigmaleo archeri gen. et sp. nov., from early Miocene deposits. Lekaneleo myersi is described from a dentary, partial maxilla and isolated teeth. It is approximately 10% larger in most linear dental dimensions than its sister taxon L. roskellyae. In this feature, it echoes the morphological cline shown by members of the Wakaleo lineage of marsupial lions, which increase their size through the Miocene. Although the first upper molar of L. myersi exhibits a tall metacone, a feature normally characteristic of species of Wakaleo, other features of its upper and lower molars support its attribution to Lekaneleo. Enigmaleo archeri gen. et sp. nov. is described from an isolated upper third premolar. This species is smaller than those of Lekaneleo, but larger than Microleo attenboroughi, the smallest known thylacoleonid. This premolar exhibits an intriguing combination of features, some of which are seen in Microleo and others in Lekaneleo, and on this basis is attributed to a new genus. It is the fourth thylacoleonid taxon from early Miocene deposits, making this time the most diverse period in thylacoleonid evolution. Phylogenetic analysis of 53 dental and 16 cranial characters recovers Enigmaleo as the sister taxon to Microleo, with this clade forming the sister group to the rest of the thylacoleonid family; however, the relationships among species of Lekaneleo was not resolved in this analysis. Comparisons of the morphology of the upper third premolars of all thylacoleonid taxa indicate that the evolution of the Thylacoleo form is more likely to have been derived from a Microleo or Enigmaleo form, and on this basis it is postulated that one of these groups may have provided the ancestor of the Thylacoleo lineage.Anna Gillespie [], Earth and Sustainability Science Research Centre, School of Biological Earth and Environmental Science. University of New South Wales 2052, Sydney, Australia.