Research Sheds More Light on Enigmatic, Long-Extinct Nimbadon

According to a new research led by Dr Karen Black of the University of New South Wales, Nimbadon lavarackorum – a large bear-like animal that lived in Australia’s lush forests 15 million years ago – was well suited to life in the treetops: it used massive sharp claws to haul its hefty body up trees, hugging the trunk like a bear, and its huge hands and long arms let it hang from branches like an orangutan.

This is an artist’s reconstruction of Nimbadon mother and juvenile (Peter Schouten)

“Because of their large size and abundance in the fossil record, it has generally been accepted that most diprotodontoids (an extinct family of large, actively mobile marsupials) were terrestrial and roamed in herds or mobs like modern-day kangaroos,” Dr Black explained. “Our study has turned many of these long-held preconceptions about the lifestyles of these marsupials literally on their heads.

“We compared some exceptionally well-preserved Nimbadon skeletons from a fossil cave in the Riversleigh World Heritage Area with those of a range of modern and extinct mammals of varying lifestyles. Strikingly, we found Nimbadon‘s skeleton – in particular its limbs, hands and feet – to be most similar to that of the living koala.”

Like the koala, Nimbadon possessed powerful forelimbs with highly mobile shoulder and elbow joints that would have allowed significant extension and rotation of the arms, an essential trait for climbing through a tree canopy and for balancing on tree branches.

Nimbadon‘s hands and feet were extremely large, with long, flexible fingers and toes and semi-opposable first digits. Combined with the deep carpal tunnel of the wrist, it probably possessed an exceptionally powerful grasp.

Nimbadon’s massive, sharp, recurved claws on its hands and feet were identical to those of the koala – but far larger – and could deeply penetrate a tree trunk during climbing.

“Our study showed that claws of this kind are only found in species that live in or regularly climb trees,” Dr Black said. “The numerous similarities between koala and Nimbadon skeletons suggest they functioned in much the same way and that Nimbadon used a trunk-hugging climbing method.”

Nimbadon had the shortest hind-limbs relative to its forelimbs of any known marsupial. Those same limb proportions are found today in animals such as sloths and some apes that regularly hang by their forelimbs from tree branches. It is a behavior no longer regularly used by any marsupial.

Like some tree-climbing bears, it’s possible that Nimbadon may have supplemented its diet with fruit and possibly played a role as a large seed disperser in Australia’s ancient forests. Its climbing ability would have allowed it access to multiple layers of the rainforest canopy, perhaps to reduce competition for resources with terrestrial kangaroos and also for protection from predators. These findings were published online in the journal PLoS-ONE.

“Our study indicates that modern Australian ecosystems have suffered an even greater loss in ecological diversity than previously expected,” Dr Black concluded.

_______

Bibliographic information: Black KH et al. 2012. Herds Overhead: Nimbadon lavarackorum (Diprotodontidae), Heavyweight Marsupial Herbivores in the Miocene Forests of Australia. PLoS ONE 7 (11): e48213; doi: 10.1371/journal.pone.0048213