Quirks & Quarks

Ancient beavers as big as bears died out because of their woodless diet

As the landscape dried up 10,000 years ago this dam-less beaver couldn't create it's own home

As the landscape dried this dam-less beaver couldn't create it's own home

Tessa Plint with life size giant beaver statue at Yukon Beringia Interpretive Centre. (Tessa Plint)
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10,000 years ago giant beavers weighing 100kg, and standing two meters tall disappeared into extinction. Now scientists think they know why.

Researcher Tessa Plint studied giant beaver fossils when she was in the Department of Earth Sciences at Western University in London, Ontario. Her work revealed that these less-than industrious giant rodents didn't eat wood or make dams and as a result had nowhere to live when the climate changed at the end of the last ice-age

Giant beaver skeleton. (Canadian Museum of Nature)

A tale of two beavers

Even though the beavers we see today and giant beavers co-existed for tens of thousand of years, the mega version - about the size of a small black bear - was quite different. Their size was one difference. They also lacked the distinctive paddle-shaped tail of today's beaver.

But Plint's work has revealed that the most important factor in their extinction might have been that they lacked a taste for wood. 

Isotope analysis of fossil bones and teeth revealed that they survived on a diet of submerged aquatic plants in their wetland habitat. They did have large incisors, but those teeth did not have the thin, chisel-like edge of beaver teeth today.

Instead they were rounded, similar to bananas in shape and size. This made them better suited to eating softer plants. 

Giant beaver by comparison. (Scott Woods)

Why we don't see the giant beaver today

At the end of the Pleistocene just over 11,000 years ago, nearly all of Canada and the northern United States was covered in ice. As the ice sheets retreated, the climate became warmer and drier. This was not good news for the giant beavers because their wetland habitats began to dry up all across North America.

Unlike their smaller relatives, the giant beavers were not able to build dams and change the landscape to create their own wetlands.

The teeth of the giant beaver were more rounded and not as sharp of those of the modern beaver, and therefore not suited to chewing or eating wood. (Florida Museum of Natural History)

The fossil record suggests an isolated population existed in the lowlands south of the Great Lakes until competition for space and the ongoing change in climate ultimately contributed to their extinction about 10,000 years ago. It was one of the last surviving members of the Pleistocene megafauna community in North America, along with mastodons and wooly mammoths.  

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