Humans Caused Australia's Ice Age Extinctions, Tooth Study Says

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Two new species of tree kangaroos, for example, indicate that 300,000 years ago Nullarbor Plain wasn't as treeless as its name implies.

Researchers also found lizards that favor dry conditions and a high ratio of grazing species.

But the most telling clues, the team says, come from an analysis of tooth enamel from 13 species of ancient kangaroo and a giant wombat.

Isotopes found in tooth enamel can signal the abundance of standing water and certain types of grasses.

Researchers compared their results with a database of similar studies of enamel from modern-day kangaroos and wombats.

The results, reported in tomorrow's issue of the journal Nature, show that Nullarbor was as parched back then as it is now.

Tipping Point

According to John Long, a paleontologist at Museum Victoria and study co-author, the findings "have virtually nailed that climate change wasn't a major factor" in the animals' extinction.

"We were able to establish that this entire assemblage of [Ice Age] megafauna animals was adapted to aridity."

Australia's Ice Age creatures probably employed adaptations like those found in modern kangaroos, the paleontologist said.

Living 'roos can survive on the water from plants alone and time their reproductive cycles to coincide with rainy periods.

Roberts, the Wollongong geologist, said Australia's ancient animals "already were very well adapted to some pretty awful climates, and they didn't get any worse than they did on the Nullarbor Plain."

He notes that a recent study in the journal Geology by many of the same team members suggests that Australia's megafauna were very resilient to climate change.

The scientists therefore believe that hunting pressures and wildfires linked to ancient humans may have finally tipped the balance against Australia's large animals.

As climate shifted, the animals suffered, Roberts said. "But they always bounced back—except about 40,000 to 50,000 years ago, [after which] they never bounced back.

"And the only difference is that people were around on the scene at that stage."

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