Badjcinus turnbulli, gen. et sp. nov., is described from dental and incomplete skull material that includes the only pre-Pliocene dasyuromorphian basicranium described to date. Phylogenetic analysis places B. turnbulli basally within the Thylacinidae, but with autapomorphies. The relationship of B. turnbulli to other thylacines is assessed. The breadth of thylacinid diversity evident during the middle Tertiary argues for an earlier origin for the family than that suggested by molecular-based investigations. An amended diagnosis of the Thylacinidae is presented and thylacinid diversity and ecology is discussed.