Predatory behaviour of extinct ‘cat-like’ marsupial carnivore

Nimbacinus dicksoni was a cat-sized marsupial carnivore from the family thylacinidae, weighing approximately 5 kg. Fossils of Nimbicinus have been discovered in Tertiary deposits in Riversleigh, north-western Queensland and Bullock Creek, Northern Territory.They belong to the extinct family Thylacinidae, which comprises of 12 species, the oldest of which are Late Oligocene in age.

Its dentition is typical of a carnivore, and shares dental characteristics similar to today’s spotted-tailed quoll. The teeth of Nimbacinus are less specialised than the recently extinct thylacine. Excepting the recently extinct thylacine, most species from Thylacindae are known from only fragmentary craniodental material. However, a particularly well-preserved skull of the fossil species Nimbacinus dicksoni has been recovered from early-late Miocene deposits of Riversleigh in northwestern Queensland.

To find out whether Nimbicinus specialised in small or large sized prey, I have digitally reconstructed its skull and applied three-dimensional computer modelling software to compare mechanical performance between it and other marsupial carnivores. This manuscript is currently under peer review.

History of Thylacinidae

The fossil history of Thylacinidae in Australasia dates back some 23 million years, and has revealed surprising diversity. Twelve fossil species from this family are now known and are separated into nine genera. The smallest known thylacinid, Mutpuracinus archibaldi weighed 1.1 kg and the largest, Thylacinus megiriani weighed over 57 kg . Differences in body size among thylacinids may have facilitated partitioning of prey species in regions where they likely co-existed. All members of Thylacinidae, except the thylacine, became extinct by the Pleistocene. Mummified thylacine remains found in caves of Western Australia reveal the first traces of modern thylacines, dated between four and five million years old. The species was once widely distributed across continental Australia but was wiped out from the mainland around 3000 years ago and possibly earlier in New Guinea. This coincides with the local extinction of Tasmanian devils, which persisted on mainland Australia until around 3000 to 4000 years ago.

Where did they live?

The early to middle Miocene thylacinids of Riversleigh in Queensland inhabited rainforests. Drying of the Australian continent lead to the gradual replacement of forest environments with open shrublands and grasslands. These changes appear to broadly correlate with declining diversity within the family.

Why did these marsupial carnivores go extinct?

Aboriginal hunting, changed land use patterns, climate change and the presence of dingoes have been linked to the extinction of the thylacine on the continent’s mainland. Dingoes were introduced into Australia by Aboriginal people around 5000 years ago. The highly generalised diet of dingoes gave them an edge over mainland thylacines and they likely outcompeted thylacines for shared food resources. Dingoes and male thylacines were similarly sized, while female thylacines were much smaller. Potential killing of female thylacines by dingoes would have reduced the reproductive output of thylacine populations. Expansion of the human population on the mainland about 4000 years ago, together with improved hunting technology, increased hunting pressure on large vertebrates including Tasmanian devils and thylacines. A small population of thylacines persisted on the remote island of Tasmania where there were no dingoes. No more than 3000 thylacines were estimated to be present in Tasmania by the time the British colonised Australia in 1789.