Maximucinus muirheadae, gen. et sp. nov. (Thylacinidae : Marsupialia), from the Miocene of Riversleigh, north-western Queensland, with estimates of body weights for fossil thylacinids

Abstract

An eighth genus and twelfth species of Tertiary thylacinid is described. This new taxon represents the seventh member of the family from the fossiliferous Carl Creek limestones of Riversleigh, north-western Queensland. Although plesiomorphic within Thylacinidae regarding most features and lacking synapomorphies that unambiguously unite it with specialised taxa within the family, it possesses two autapomorphies. With an estimated body weight of around 18 kg it is also larger than any previously known thylacinid predating the late Miocene. Body-weight estimates for remaining fossil Thylacinidae span a wide range from just over 1 kg to almost 60 kg. While the smallest species is comparable to the extant Dasyurus viverrinus in size, most (i.e. 9 of 12 taxa) are at least twice the average size of the living Dasyurus maculatus. These results suggest that trophic diversity among thylacinids is even greater than previously thought and detract from the argument that reptiles have dominated large terrestrial carnivore niches in Australia since at least early Miocene times.