Nimbacinus dicksoni was a cat-sized marsupial carnivore from the Thylacinidae family, weighing around 5 kg. It roamed the Australian landscape during the Miocene, and its fossils have been uncovered in Tertiary deposits at Riversleigh in north-western Queensland and Bullock Creek in the Northern Territory. Nimbacinus belonged to the extinct Thylacinidae family, which includes twelve species, some of which date back as far as the Late Oligocene.
With its sharp teeth and carnivorous dentition, Nimbacinus was a skilled predator, its dental features resembling those of today’s spotted-tailed quoll. However, its teeth were less specialised than those of the thylacine, the most famous member of the family, which only went extinct in modern times. While much of the Thylacinidae family is known only from fragmentary fossils, a particularly well-preserved skull of Nimbacinus dicksoni has been recovered from Riversleigh’s early to late Miocene deposits.
Research project
The study of Nimbacinus dicksoni, a middle Miocene marsupial carnivore, aimed to determine whether it was a specialist in hunting small or large prey. By digitally reconstructing its skull and using three-dimensional Finite Element Analysis (FEA), we compared the skull’s mechanical performance with that of three extant marsupial carnivores and the recently extinct thylacine.
The findings revealed that the stress distributions and magnitudes in the skull of Nimbacinus closely resembled those of the living spotted-tailed quoll, rather than the thylacine. This suggests that Nimbacinus likely shared a similar ecological niche with the quoll, capable of hunting vertebrate prey, potentially even those exceeding its own body mass. These results indicate that Nimbacinus was adapted to hunt relatively large prey, much like the modern spotted-tailed quoll, rather than the smaller prey typically hunted by its extinct relative, the thylacine.
The Fossil History of Thylacinidae
The Thylacinidae family’s fossil history in Australasia spans 23 million years and reveals a surprising diversity of species. In total, twelve fossil species from nine genera have been identified. The smallest known thylacinid, Mutpuracinus archibaldi, weighed just 1.1 kg, while the largest, Thylacinus megiriani, tipped the scales at over 57 kg. The variation in size likely allowed these species to co-exist and specialise in different prey types in their overlapping territories.
While most thylacinids became extinct by the Pleistocene, a small population of thylacines managed to survive on Tasmania until the early 20th century. Mummified remains of thylacines found in caves in Western Australia, dating back 4–5 million years, represent some of the earliest evidence of these creatures. Once widespread across continental Australia, thylacines disappeared from the mainland around 3000 years ago, possibly driven to extinction by the arrival of dingoes, a shift in climate, and human hunting pressures.
Where Did Thylacinids Live?
The early to middle Miocene thylacinids from Riversleigh thrived in rainforests, a lush environment that offered ample prey. However, as Australia’s climate gradually dried, forests gave way to open shrublands and grasslands. This shift in habitat seems to correlate with a decline in the diversity of Thylacinidae species, as these changing landscapes would have affected the availability of suitable prey and altered the predators’ hunting strategies.
Why Did These Marsupial Carnivores Go Extinct?
The extinction of the thylacine on mainland Australia is thought to be a result of multiple factors, including Aboriginal hunting, climate change, habitat loss, and the arrival of dingoes. Dingoes were introduced to Australia around 5000 years ago and quickly established themselves as dominant predators. Their highly adaptable diet likely gave them an edge over thylacines, as they outcompeted the more specialised thylacines for resources. Dingoes and male thylacines were similarly sized, but female thylacines were much smaller, which may have led to their vulnerability. The potential killing of female thylacines by dingoes would have significantly reduced their reproductive output.
The spread of human populations around 4000 years ago, along with advancements in hunting technology, further increased hunting pressures on large vertebrates, including thylacines and Tasmanian devils. By the time British colonisers arrived in 1788, fewer than 3000 thylacines remained in Tasmania, the last refuge of the species. Despite surviving on the island, thylacines were not immune to the pressures of human expansion, and the species was officially declared extinct in 1936.
The story of Nimbacinus and its Thylacinidae relatives offers fascinating insights into the predatory behaviour and ecological niches occupied by these now-extinct marsupial carnivores. Understanding their history and the factors that led to their extinction can help inform conservation efforts for other endangered species today.
Marie Attard 