Woolly mammoths died out with the invasion of grasslands more than 10,000 years ago according to Eske Willerslev, the head researcher at centre of geogenetics at the University of Copenhagen.

In his article 'Fifty thousand years of Arctic vegetation and megafaunal diet, published in this week's edition of Nature, the Danish researcher claims to have discovered the "smoking gun" behind Ice Age megafauna mass extinction. 

Willerslev and his team of international colleagues studied frozen stomach contents and frozen DNA found in the dirt across the Arctic. Their results suggest that the Ice Age megafauna like mammoths and woolly rhinos primarily ate a richer class of plants called forbs.

But the diversity of forbs diminished with the largest glacial period 15,000-25,000 years ago, when the climate was coldest and driest. As the climate got warmer around 10,000 years ago, grasses replaced the mammoths’ favourite diet, causing almost all large Arctic mammals to starve to death.

"Our study really changes the general concept that before the last warming period you had a massive grass steppe that was fundamental to sustaining a huge diversity of mammals," Willerslev told New Scientist magazine. "In fact it was a diverse steppe of forbs and these were probably crucial."

A smoking gun
Scientists have long argued that climate change was the reason behind the Ice Age megafauna extinction, but until now they have lacked a 'smoking gun'.

"We knew from our previous work that climate was driving fluctuations of the megafauna populations, but not how," Willerslev said. "Now we know that the loss of protein-rich forbs was likely a key player in the loss of the Ice Age megafauna."

Willerslev added that the results may also cast light on current climate change.

"Maybe we get a hold on greenhouse gases in the future," he said. "But don’t expect the good old well-known vegetation to come back when it becomes cooler again after the global warming."