FEATURE: Giant kangaroo extinction mystery

Researchers in Australia have put forward a theory that a species of giant kangaroo, weighing more than 200 kilograms, was hunted to extinction by humans 45,000 years ago.

But the hunting theory has been challenged by other researchers as a leap of faith based on scant evidence, with many suggesting climate change played a part in wiping out the massive marsupials.

Liam Cochrane

Last Updated: Thu, 25 Jun 2009 12:23:00 +1000

Australian's favourite kangaroo Skippy became an international icon thanks to a 1960s TV show.

But go back a bit - say between 500,000 years ago and 45,000 years ago, Australia was home to Skippy's giant ancestor - the procoptodon goliah.

It stood more than two meters tall, weighed 230 kilograms and had a face more like a koala than today's kangaroos.

It was one of dozens of species of megafauna - including a wombat the size of a hippopotamus, a giant goanna and marsupial lion.

Scientists have long wondered what wiped out these huge animals; with climate change, fires started by humans and hunting the most popular theories.

But a new research paper in the Proceeding of the National Academy of Sciences of the United States has reignited the debate by making the case that hunting was responsible for the extinction of the giant kangaroo.

Gavin Prideaux, a palaeontologist from Flinders University was one of the authors.

"Rather than providing direct evidence of human hunting having caused the extinction, we essentially undermine the validity of the alternatives," he said.

"Because what we established was that climate change, in the form of increased aridity, could not have caused this extinction because these animals evolved in response to increased aridity. They were widely distributed throughout arid Australia, they ate the types of plants that grow in these dry regions, [and] they were very well adapted to arid conditions."

Most likely scenario

Dr Prideaux also says the type of plants eaten by megafauna don't allow fires to spread easily.

"There are two reasons for that: one - salt bush doesn't actually burn very well. If a lightning strike hit the salt bush, it will burn, but then fire doesn't pass from one bush to the next very well, because in the shrub lands out in the dry parts of Australia, the bushes are quite well spread apart, and there's not much to burn in-between," he said. "And that leaves hunting as the most like scenario."

By studying the oxygen isotopes on the fossils Dr Prideaux and his colleagues concluded that the giant kangaroo had to drink more water than other megafauna.

As a result, Dr Prideaux says, these visits to the precious oases of water in the arid landscape would have probably brought them into contact with humans and their desire for a bit of roast kangaroo.

"Certainly, they would have been very slow and cumbersome to begin hopping," he said.

"They probably would have moved along fast in full-flight, but they would have been slow to start and therefore susceptible to hunting."

No evidence

But the hunting theory has been challenged by archaeologist Judith Field from the University of Sydney.

"What they're doing is they're saying 'well, we've shown these animals adapted to aridity - ispo facto they can't have died because of aridity, and therefore humans must have killed them' - on which there is absolutely no evidence to suggest it," she said.

"The absence of evidence of one thing doesn't mean you can evoke an explanation which doesn't have any evidence to support it either."

Dr Field also says the dates may not match up.

"Most megafauna - and there must be nearly 70 species of megafauna now known - 65 per cent of these animals can now not be placed within 100,000 years of human arrival," she said.

"So they disappeared 100,000 years before humans set foot on the continent. Now if you're going to start attributing blame to humans for the megafaunal extinctions, you have to place most, if not all, of those animals around when people arrived, for it to be a human driven event."

Solving the puzzle

Dr Prideaux says there was at least 5,000 years of overlap between humans and giant kangaroos.

And he says, 45,000 years ago humans hunted animals which still exist today - such as eastern gray kangaroos like Skippy - so hunting doesn't necessarily equate to extinction.

But Dr Field remains sceptical.

"I think it's something we're going to puzzle over for many years to come," she said.

And Dr Prideaux believes the diet of the giant kangaroo gives us the key clue to their extinction, but more evidence is needed.

"If we're really going to solve this question, we need good evidence on what ecological role all of the other species that became extinct were playing in the landscape," Dr Prideaux said.

"We need to understand what was it that made those animals that became extinct more susceptible than what those that came through to the present day. That's a big thing to solve."