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Ancient Beavers Take Silver in Log-Chomping Olympics

14 August 2008 (All day)
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Martin Lipman/Canadian Museum of Nature

Chew on this. This fossilized log was found in a peat bog high on Ellesmere Island.

Call it The Great Gnaw-Off. By studying logs chomped nearly 5 million years ago, researchers have discovered that ancient beavers weren't nearly as expert lumberjacks as their modern cousins. Indeed, the evidence suggests that they would have been trounced by today's beavers in a tree-cutting Olympics. Researchers say the finding provides rare insight into how one of the animal kingdom's busiest critters may have shaped ancient landscapes.

"Beavers are really major ecosystem engineers, but we don't really have a good picture of their past roles," says study author Natalia Rybczynski, a paleobiologist at the Canadian Museum of Nature in Ottawa. To fill in that picture, Rybczynski has been studying some beaver fossils and chewed logs, branches, and twigs pulled from a peat bog high in the Canadian Arctic. Originally discovered in the 1960s, the site on Ellesmere Island is known for its rich lode of mammal fossils. And the gnawed wood is believed to be the oldest evidence of beaver activity ever found, dating back 4 million to 5 million years. The trees are "so well preserved you could burn them," she says.

In the current issue of Paleobiology, Rybczynski identifies the extinct beaver that chewed on those trees: a rodent named Dipoides that was about two-thirds the size of its modern relatives. To find out how its logging skills compared with those of today's beavers, Rybczynski did some painstaking--and unusual--research. She went to a zoo to videotape the eating behavior and dental work of a family of five beavers, for instance. And she spent hours carefully measuring and drawing the teeth and bite marks made by both modern and fossil rodents. She even built metal replicas of beaver teeth for a study--still under way--on the physics of gnawing.

The upshot, she says, is that even after adjusting for its smaller size, "Dipoides was pretty laborious, pretty slow, and not very good at cutting stuff up. He just wasn't nearly as efficient as existing beavers."

That suggests Dipoides may have had a hard time building the elaborate dams, huge ponds, and dome-shaped lodges that are the hallmark of today's beavers, Rybczynski says. In fact, there's no obvious evidence of dams or lodges at the Canadian site. That might be because Dipoides used another strategy, such as hibernating in a burrow or nest, to survive harsh winters. In the end, though, the animal's lack of advanced woodworking skills could be one reason it ultimately became extinct.

It's rare to discover such a good example of mammal fossils together with their munchies, says Jin Meng, a paleontologist at the American Museum of Natural History in New York City. "Finding the wooden sticks with the marks right there is remarkable. That association allows you to do much more detailed analyses," he adds--such as exactly how much wood a, ... well, beaver ... could cut.