A Hop Skip and a Jump into a Time Capsule

Researchers in Australia are hopping with excitement having uncovered some of the most pristine fossils ever found in Australia, including 8 new species of kangaroo. The finds also tell a very different story of Australia in the past. Writing in this week's Nature, researcher Gavin Prideaux and his colleagues describe how they found a limestone cave in south-central Australia's treeless Nullarbor Plain. The entrance to the cave has periodically been opened and closed by natural events, and these have helped to keep the contents, which Prideaux describes as "the rosetta stone for scientists trying to understand past Australian climate", in excellent condition. "What must have happened is that animals fell into the cave, but they didn't die immediately. Instead they wandered away a short distance and so their remains are undisturbed." So far the team have dug through sediments at least three-quarters of a million years old and turned up the remains of birds, reptiles and 23 kangaroo species including 8 which have never been described before. But what is really exciting the team now are the clues that these remains provide to how Australia's climate must have changed in the last million years or so. The animals they've found are large herbivores; some of them would have weighed several hundred kilograms. But the Nullarbor plain is almost devoid of greenery and certainly couldn't have sustained such big plant-eaters, so the area must have been much richer in vegetation in the past. So did the climate change and turn a lush pasture into a treeless desert? No, says Prideaux, because stable oxygen and carbon isotopes in tooth enamel from the site can be used to calculate a record of past climate. These results show that the climate in this part of Australia, when these animals roamed, was almost identical to how it is today. So what's caused this transformation? "Wild fires," says Prideaux. And where did they come from. One word. Humans. "Most of these species were extinct by or soon after 40,000 years ago, at around the time when humans reached the south central coast."