Why Giant Beavers Went Extinct 10,000 Years Ago

Giant beavers (members of the genus Castoroides) inhabited North America throughout the mid- to late Pleistocene. They went extinct along with dozens of other megafaunal species at the end of the last Ice Age, approximately 10,000 years ago. Now a team of researchers in Canada has uncovered a possible reason of their extinction: vanishing food source. More importantly, the scientists have discovered that these enormous rodents did not eat wood — a distinct divergence from their dentally-endowed descendants.

Giant beavers, about as large as a modern-day bear, ate aquatic plants before they went extinct after the last Ice Age. Image credit: Luke Dickey.

Giant beavers, about as large as a modern-day bear, ate aquatic plants before they went extinct after the last Ice Age. Image credit: Luke Dickey.

Tessa Plint of Heriot-Watt University and her colleagues from the University of Western Ontario, Yukon Palaeontology Program and the Canadian Museum of Nature used stable isotopes of fossil bones and teeth to determine the diet of the now-extinct giant beavers.

The researchers found that the beavers ate submerged aquatic plants (macrophytes).

This diet made the rodents, which weighed approximately 100 kg, highly dependent on wetland habitat not only for shelter from predators but also for food.

“We did not find any evidence that the giant beaver cut down trees or ate trees for food,” Plint said.

“Giant beavers were not ‘ecosystem-engineers’ the way that the North American beaver is.”

Beavers (members of the genus Castor) and giant beavers actually co-existed for tens of thousands of years in North America during the Pleistocene epoch before the latter went extinct.

After the last Ice Age, the ice sheets retreated and the climate became much drier. This climate change was bad news for giant beavers.

“The ability to build dams and lodges may have actually given beavers a competitive advantage over giant beavers because it could alter the landscape to create suitable wetland habitat where required. Giant beavers couldn’t do this,” said Professor Fred Longstaffe, from the University of Western Ontario.

“When you look at the fossil record from the last million years, you repeatedly see regional giant beaver populations disappear with the onset of more arid climatic conditions.”

The findings were published in the journal Scientific Reports.

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Tessa Plint et al. 2019. Giant beaver palaeoecology inferred from stable isotopes. Scientific Reports 9, article number: 7179; doi: 10.1038/s41598-019-43710-9

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