Timothy McDonald reported this story on Friday, January 22, 2010 08:13:00

ELEANOR HALL: A menagerie of curious species, ranging from a Rhinoceros-sized wombat to a sheep-sized echidna, once roamed the Australian continent.



Most died out long before European settlement.



But two researchers, who've just published a paper in the journal, Science, say there's now compelling evidence that humans are responsible for the demise of the super-sized animals.



This theory, though, is contested by an archaeologist who's been conducting research at one of Australia's most significant archaeological sites.



As Timothy McDonald reports.



TIMOTHY MCDONALD: When English naturalists were first presented with the preserved specimen of a Platypus, they thought it was so bizarre it must have been a hoax.



Imagine then what they might have thought had they been faced with a wombat the size of a small car, or one of the many other fanciful creatures that died out long before Europeans ever arrived in Australia.



BARRY BROOK: There was an ancient possum which was a carnivore about the size of a lion; and there was a huge lizard, like a goanna, but about six-metres long; and there was a bird, bit like an emu, but about twice as heavy and half as tall again.



TIMOTHY MCDONALD: Barry Brook is a Professor of Climate Change at the University of Adelaide's Environment Institute.



He says a debate has raged for some time over why these creatures vanished. Some have argued that climate change killed them off.



But Professor Brook says the evidence is now extremely strong that humans were the cause.



BARRY BROOK: Everywhere we look in Australia, it seems that there was a very short overlap between people and megafauna.



TIMOTHY MCDONALD: At the centre of a the debate is site in western New South Wales, called Cuddy Station, where archaeologists have found the remains of megafauna as well as stone tools, leading some to believe that there was a lengthy overlap between humans and Australia's largest animals.



Barry Brook says new dating methods indicate that many of the bones are much older than the tools, suggesting that if humans and megafauna did co-exist, they didn't do it for very long.



He says the tools and the bones may have been washed there in a flood, which explains why they were found in the same layer of sediment.



BARRY BROOK: It's quite clear in fact that a lot of these are old bones that have been eroded out of a river bank or some other deposit and washed down there and then redeposited and in the stone tools have been mixed in with it.



TIMOTHY MCDONALD: But the theory is disputed by Judith Field, who's an honorary research fellow in archaeology at the University of Sydney. She's studied Cuddie Station for more than a decade and says there's no evidence that a flood pushed all the detritus into one big pile.



JUDITH FIELD: What we have here are bones lying in a deposit in an anatomical order in some case. So it's quite clear that the animal died where it dropped and it's been enclosed by very, very fine grain clothes and silk.



Not only that but the stone tools around them are very sharp, have been used, and are very clearly not been washed in from anywhere.



TIMOTHY MCDONALD: Dr Field says it's more likely that the extinctions didn't occur as one mass event, and instead occurred slowly over tens of thousands of years.



She says it's clear that many species died out well before humans arrived, but there's scant evidence to say definitively how Australia's megafauna died out.



ELEANOR HALL: Timothy McDonald reporting.