Extinct wombat climbed trees like a koala

By Natalie Muller 22 November 2012
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Fossils have shed light on a wombat-like creature that once lived in Australia’s rainforest canopies.

FOSSILISED REMAINS OF AN early relative of the wombat suggest that the marsupial lived in treetops around 15 million years ago.

The ancient bones, uncovered in an outback Queensland cave in the 1990s, could be the remains of the largest known tree-climbing marsupial, according to new research.

Scientists from the University of New South Wales and the University of Adelaide examined the skeleton of the species, known as Nimbadon lavarackorum, which was discovered at the Riversleigh World Heritage fossil field. The research revealed that the 70kg marsupial was equipped with powerful limbs to scale tree trunks.

Dr Karen Black, a palaeontologist from UNSW’s School of Biological, Earth and Environmental Sciences, says it was a surprise discovery given the animal’s hefty size and close ties to the wombat.

“To have a wombat-like animal up a tree was pretty amazing,” Karen says. The largest tree-climbing marsupial alive in Australia today is the Bennett’s tree kangaroo, which can weigh up to 14kg.

Extinct marsupial climbed trees like a koala

The scientists compared the Nimbadon skeleton with bones from living animals such as the koala, brushtail possum and Malayan sun bear. Honing in on the limbs, hands and feet, the study found the Nimbadon had the most in common with the koala.

“It had highly-mobile shoulder, elbow and wrist joints, so it was flexible for grabbing branches and climbing,” says Karen. “It also had very large hands and feet with opposable thumbs, and massive claws almost identical to a koala’s.”

Karen says these traits suggest that Nimbadon behaved similarly to the modern-day koala, using the same trunk-hugging method to climb trees.

Skeleton of extinct wombat-like tree dweller known as <EM><noscript><img decoding=Nimbadon lavarackorum“>
Skeleton of extinct wombat-like tree dweller known as Nimbadon lavarackorum.

But Karen says the team also found some highly unusual characteristics. The Nimbadon had relatively short hind limbs, suggesting it may have hung from branches like a sloth or orangutan.

The marsupial also sported a unique bulbous snout. “Maybe it was detecting rainforest fruits with its big nose, so it possibly could have played a role as a large seed disperser in Australia’s rainforest, which no living marsupial in Australia does,” Karen says.

Fossils reveal Australian fauna evolution

It is believed the Nimbadon died out about 15 million years ago. It was around this time that Australia’s rainforests began to recede, gradually being replaced with drier landscape.

Associate professor Rod Wells, a palaeontologist at Flinders University in Adelaide, says piecing together Australia’s early fossil record, dating back to eras such as the Miocene period, is no easy task.

“This paper represents a step beyond phylogeny [the family tree of a species],” Rod says. “It is important in that it gives us an all too rare insight into the biomechanics and behaviour of a middle Miocene marsupial, arguably Australia’s largest arboreal herbivore.”

Rod hopes further research will lead to greater insights into the evolution of Australian mammal and marsupial fauna.

The findings were originally published in scientific journal PLOS ONE.