Fossil Study Sheds Light on Largest Tree-Dwelling Marsupials

A new study on Nimbadon skeletons has revealed the lifestyle and ecology of the species that lived during the Middle Miocene period, 15 million years ago.

Nimbadons are wombat-like herbivores that belong to the extinct family of marsupials called diprotodontoids. This group also includes the largest mammals in Australia for the last 25 million years up until their extinction around 30,000 years ago.

A team of Australian researchers examined around 30 Nimbadon skulls and abundant skeletons that were recovered from the AL90 fossil cave in Queensland, Australia. These samples represent individuals ranging in age from pouch young to elderly adults.

Based on their observations, the research team has revealed the unexpected features, habitat and lifestyle of the extinct mammals.

The abundance of Nimbadon fossils found together in the cave suggests that these animals roamed in groups. Experts found that the Nimbadons had relatively forward-facing eyes and an unusual short, bulbous snout. This might indicate that the animals had an enhanced olfactory capacity (sense of smell) to detect rainforest fruits.

Experts also noticed similarities between the ancient mammal's skeleton and living koalas. The Nimbadons had strong forelimbs with highly movable shoulder, elbow and wrist joints, but had short hindlimbs.

They also possessed long, flexible fingers and toes, and sharp, re-curved claws. These features suggest that the Nimbadons were tree-dwelling mammals. It shows that they had strong climbing and grasping skills.  Their forelimbs indicate that the animals used a trunk-hugging method of climbing.  

Their flexible arms would have helped them hang from tree branches and reach for food, LiveScience reported. They might have used their sharp claws to deeply penetrate the tree trunk while climbing, said the researchers. Although the diprotodontoids were thought to have lived on the ground, the Nimbadon features show evidence that they lived in trees.

Today, the biggest tree-dwelling mammals in Australia are the koalas and the tree-kangaroos. The largest males of these two species weigh around 30 pounds. But the ancient Nimbadons, which roamed the treetops, weighed around 154 pounds (70 kg). This suggests that the Nimbadons were the biggest tree-dwelling herbivorous mammals to have occupied the ancient forest canopies of Australia.

"The findings presented here indicate that we are only beginning to understand the range of morphological and niche diversity displayed by this ecologically important and widespread group of Australasian marsupials - the diprotodontids," the researchers wrote in the paper.

The findings of the study, "Herds Overhead: Nimbadon lavarackorum (Diprotodontidae), Heavyweight Marsupial Herbivores in the Miocene Forests of Australia", are published in the journal PLOS ONE.