An ice age beast evolved to beat the cold

September 1, 2011

Christopher Joyce

An artist's reconstruction of the Tibetan woolly rhino. Woolly rhinos used their flattened horns to sweep snow off of vegetation, a critical adaptation to survive frigid conditions.
Digital composite photo of the skull and lower jaw of the woolly rhino.

The Tibetan Plateau is the world's highest place. It's four times the size of France and home to most of the world's highest mountains.

As you might expect, it's cold there. And it may be that the deep chill of the Tibetan Plateau played a role in the evolution of some of the world's most charismatic animals.

That's the belief of a scientist who discovered the skull of a woolly rhino on the Tibetan Plateau.

The woolly rhino — two tons, two tusks, lots of hair and lots of attitude — was an Ice Age giant. It cavorted with woolly mammoths and giant sloths and other Ice Age behemoths in Europe and Asia, starting about 2.5 million years ago.

But Xiaoming Wang, from the Natural History Museum of Los Angeles County, was shocked when he found a 3.5-million-year-old rhino skull on the Tibetan Plateau. "It caught us by complete surprise that they are actually up in the high plateau well before the Ice Age has started," Wang says.

That's about a million years before the Ice Age started, in fact. Wang thinks his discovery shows that at least some animals were prepared for the Ice Age. "At least in the case of the woolly rhino, it actually adapted itself in the cold environment in the Tibetan Plateau before the Ice Age has even started," Wang says.

The adaptations included hairiness, of course. And a big body, which actually does well in cold weather. As you increase the volume of a body — say, what's inside the skin — the body's surface area doesn't increase as much. Less surface area per volume means you can retain heat better.

And then there's that second, three-foot-long horn on the woolly rhino: It was wide and flat.

"The animal actually used it to sweep snow," Wang explains, "so they can get at the vegetation below the snow cover."

Wang says he has other Tibetan fossils of an ancient blue sheep — technically a goat — that also eventually became a citizen of the Ice Age.

So Wang thinks the Plateau was a sort of evolutionary cradle for cold-weather animals. When the rest of the world eventually iced up, they moved out of Tibet and took over.

Anthony Barnosky, a paleontologist at the University of California, Berkeley, says even now, these isolated "cradles" are important for evolution.

"The interesting thing," Barnosky says, "is on Earth today we have biodiversity isolated in certain spots, and we just never know which of those isolated places will be the cradle of evolution for the next big environmental change coming down the pike."

The only problem is that to be ready, you have to know what the next environment will be like. Or just be very lucky.

The research appears in the journal Science.

Copyright 2011 National Public Radio.