It is generally accepted that climate change led to the extinction of the mammoth and other large mammals following the last Ice Age, but an international team of researchers behind a new report in the journal Nature claims to have found the smoking gun that pinpoints which of climate change's myriad effects led to the mass extinction of large mammals.

By analyzing sediment samples from more than 10,000 years ago and the gut contents of permafrozen woolly rhinos, mammoths and other extinct Ice Age mammals, the researchers contend that vegetation changes triggered by climate change following the last Ice Age is what caused the mass extinction event.

Even though the climate warmed after the last Ice Age, the landscape was forever altered. A major loss of plant diversity, particular in protein-rich forbs (herbaceous flowering plants), likely proved fatal for species like the woolly rhino, mammoth and horses in Asia and North America, the researchers said.

"We knew from our previous work that climate was driving fluctuations of the megafauna populations, but not how," said Eske Willerslev, an ancient DNA researcher and director of the Centre for GeoGenetics at the Natural History Museum of Denmark. "Now we know that the loss of protein-rich forbs was likely a key player in the loss of the Ice Age megafauna."

Willerslev said the conclusion also offers perspective on the current climate situation.

"Maybe we get a hold on the greenhouse gases in the future. But don't expect the good old well-known vegetation to come back when it becomes cooler again after the global warming," he said. "It is not given that the 'old' ecosystems will re-establish themselves to the same extent as before the warming. It's not only climate that drives vegetation changes, but also the history of the vegetation itself and the mammals consuming it."

Willerslev and his colleagues report that the classic image of the Northern Hemisphere during the last Ice Age - one dominated by a grass steppe - is not as accurate as previously believed. The landscape was more dominated by protein-rich forbs, and after the Ice Age the forbs became rarer, leading to some large, forb-eating mammals to go extinct.

The landscape additionally changed by the growth of new kinds of vegetation and a smaller base of large herbivores, the researchers said.

"For the first time, ecologists have been able to piece together the characteristics of more complete plant communities occurring in the Arctic during the last 50,000 years," Mari Moora and Martin Zobel, vegetation ecologists from the University of Tartu, Estonia, said in a joint statement. "The new information shows clearly that the vegetation of the Late Pleistocene was rich in forbs but lost considerable diversity at the peak of the Ice Age."