New craniodental specimens that are referrable to the thylacinid marsupial, Thylacinus potens, are described from the late Miocene Alcoota Local Fauna of the Northern Territory, Australia. The remains include a largely complete maxilla and dentary, showing for the first time the anterior dentition of the dentary. The new remains indicate that Th. potens was a more variable species than previously recognised. The dentary, in particular, is more gracile, than other specimens referred to this species. A revised apomorphy-based diagnosis of Th. potens that takes this variability into account is presented. A cladistic analysis supports previous analyses that placed Th. potens in a derived position within Thylacinidae, close to the modern Th. cynocephalus. New estimations of body size are made using published regressions of dental measurements of dasyuromorphians as well as by assuming geometric similitude with Th. cynocephalus. All methods produce body mass estimates in excess of 35 kg.