Bulletin

Issue: January/February 2008

News

Skippy's ancestor a galloping kangaroo?

Dr Kear at the at Riversleigh dig site.

The recently-unveiled near-complete 25-million-year-old skeleton of one of the earliest known kangaroo predecessors might offer clues to kangaroo survival under the pressure of modern climate change.

Paleontologist Dr Ben Kear — a La Trobe University Research Fellow and Research Associate at the South Australian Museum — is working with Associate Professor Mike Westerman of La Trobe's Genetics Department on a long-term study using the latest DNA technologies to piece together kangaroo evolution and the impact of climate change on kangaroo biodiversity past and present.

Their work, which attracted media attention world-wide, was first published in the November 2007 Journal of Paleontology, where Dr Kear and fellow authors Dr Bernie Cooke (Queensland Museum), Professor Michael Archer (University of NSW) and Professor Tim Flannery (Macquarie University) described the oldest known kangaroo skeleton as 'an important piece in the evolutionary jigsaw'.

'This new species, Nambaroo gillespieae, is not quite a kangaroo,' says Dr Kear. 'It's a representative of the Balbaridae, an extinct group of ancient kangaroos that seem to have been replaced over time by the ancestors of today's lineages.

'We were blessed with a near-complete skeleton from the internationallyrenowned fossil mammal riches of the Riversleigh World Heritage Area in northern Queensland. It's from just after a major blank spot in the Australian mammal fossil record — just like the Dark Ages — where we have no rock deposits with kangaroo fossils.'

The articulated hind feet of the Nambaroo. The bones show that it may have galloped rather than hopped and may even have climbed trees.

The size of a small dog, Nambaroo had canine 'fangs' that it probably used for display — perhaps to scare competitors or attract a mate. Its most intriguing feature, its hindlimb bones, show that it probably did not hop but galloped or bounded on all fours like a brushtail possum.

Its opposable 'big toe' and flexible foot suggest it may have had limited climbing ability, like today's tree kangaroos. These characteristics suggest an evolutionary adaptation to life in tropical forest and scrub, eating leaves, fruit and fungi.

'It would be another ten million years or so before grasses started to spread across the Australian landscape, and with it kangaroos adapted to grazing and evolved to hop on their hind legs,' says Dr Kear.

The skeleton of Nambaroo gillespieae was found in a limestone boulder at the 'Quantum Leap Site' in the Riversleigh World Heritage Area. Its body seems to have been washed together with other animal remains by an ancient river system.

There was no 'Eureka moment' for Dr Kear, unlike the dramatic discovery of magnificent opalised plesiosaurs — now prominently displayed at the SA Museum — part of his other research on Mesozoic marine reptiles. The Nambaroo skeleton had to await his lengthy computing of evolutionary comparisons before its significance was teased out. Nambaroo is part of the Queensland Museum's fossil collection.

'It's a marvellous find — previously we were fortunate to discover so much as a jaw or even single tooth — but that only scratched the surface,' Dr Kear says. 'We are now able to more clearly compare these ancient roos to today's species. There's a world of work ahead but indications are that we can use fossil kangaroos as climate markers by tracing evolutionary relationships against environmental alteration on a continentwide scale.'

The species name 'gillespieae' honours Anna Gillespie, fossil preparator at the University of NSW. You can't excavate Riversleigh fossils with a brush and a dental pick like some TV scientists, says Dr Kear. You must blow the very hard limestone rock apart, very precisely, with detonation cord and then soak the blocks in acid from three to six months to dissolve the rock.