Estimating the weight of the Pleistocene marsupial lion, Thylacoleo carnifex (Thylacoleonidae:Marsupialia): implications for the ecomorphology of a marsupial super-predator and hypotheses of impoverishment of Australian marsupial carnivore faunas

Using demonstrated relationships between body mass and humeral and femoral circumferences, we calculate the weight of the only specimen of Thylacoleo carnifex known from a near-complete skeleton. Body weights of 112–143 kg were estimated for this individual, from Moree, north-western New South Wales. Extrapolating on the basis of geometric similtude, we further estimated the weight of the largest T. carnifex for which we had cranial data at 128–164 kg. Moreover, estimates for at least three of the thirteen available specimens exceeded 124–160 kg, suggesting that individuals of this size were common. Our estimates of average weight for the species range from 101 to 130 kg. These results clearly show that Pleistocene Australia had a 'large' cat equivalent and that 'large' terrestrial predator niches were not then occupied exclusively by reptiles.They may also diminish the argument that soil-nutrient deficiency constrained the evolution of large mammalian carnivores on this continent in the Pleistocene. Similarly, we posit that prima facie evidence for reptilian domination of terrestrial carnivore niches during the Miocene is wanting, although it is conceded that far more detailed investigation is required to comprehensively test these hypotheses. Earlier studies have drawn parallels between T. carnifex and sabre-toothed predators, thought to have specialised in hunting particularly large and powerful prey. Taken in the context of upwardly revised weight estimates, we argue that Pleistocene marsupial lions may have dispatched even Diprotodon-sized animals. But again, more comprehensive study, including thorough biomechanical design analysis of the post-cranial skeleton in particular, will be required to thoroughly illuminate the predatory habitus and general ecology of Australia's largest and most specialised marsupial carnivore.