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Fossil Supports Megafauna Theory

This Diprotodon is expected to have lived after the arrival of humans.

This Diprotodon is expected to have lived after the arrival of humans.

By Stephen Luntz

The discovery of a nearly complete skeleton of the largest marsupial ever to live, Diprotodon optatum, has excited palaeontologists and may throw light on the hotly debated cause of the extinction of Australia’s megafauna.

The discovery was made between Burketown and Normanton on the Leichhardt River. Prof Mike Archer of the University of NSW School of Biological, Earth and Environmental Sciences says that relatively few diprotodons have been found in northern Australia, but he believes this has more to do with the lack of sites that preserved their bones than their rarity in the area.

Preliminary estimates of the fossil’s age suggest that the distant relative of the wombat lived 100,000–200,000 years ago. However, Archer says that a more accurate estimate, to be obtained by optically stimulated luminescence dating, may put it later than the arrival of humans in the area.

Archer is a supporter of the theory that the megafauna were wiped out by climate change rather than hunting. “Every specimen of megafauna from this era that has been found that shows no clear evidence of human involvement in its death adds to the assumption humans had nothing to do with it,” he says.

The cause of death in this case appears to be predation by giant lizards, as broken-off teeth from these extinct predators were found with the bones. Like modern goannas or komodo dragons, the lizards of the era were not able to chew bones. As a result the skeleton was left largely intact, with only a few bones currently missing.

Archer says that the animal in question was quite elderly, would have weighed 3 tonnes and stood 2 metres high at the shoulder.

The discovery was made with the help of local children. “Their father was a fossil enthusiast and these kids are fossil addicts,” Archer says. “They led us down the river to the site.”

The Leichhardt River is a rich source of fossils, although Archer says it has been neglected since the discovery of Riversleigh.

While the find in this case is significant for its near-completeness, Archer says that one made nearby may turn out to be even more interesting. “We found a skull that has teeth like a diprotodont but has a totally different skull, looking more like a primate with big flaring nostrils.”