Why Did These Human-Sized Beavers Go Extinct During the Last Ice Age?

Just over 10,000 years ago, 7-foot-tall beavers weighing upwards of 220 pounds roamed vast stretches of North America, populating wetlands and lakes from Alaska and Canada to Florida. But toward the end of the last ice age, these giant rodents—as well as woolly mammoths and similarly iconic prehistoric megafauna—suddenly vanished, driven to extinction under still-mysterious circumstances.

A new study conducted by a team of Canadian researchers offers a potential explanation for the black bear-sized beavers’ disappearance. As scientists led by paleogeologist Tessa Plint of Ontario’s Western University report in the journal Scientific Reports, isotopic analysis of 50,000- to 10,000-year-old beaver bones recovered from Yukon, Canada, during the 1970s has revealed that the animal survived on a heavily aquatic plant-based diet. When the last ice age drew to a close some 10,000 years ago, North America’s wetlands became increasingly warm and dry, eliminating both the species’ habitat and its main source of sustenance.

“I think anytime anyone sees [a] giant beaver skull, they’re like, ‘Wow, it must have been a sabre-tooth cat and eating people,’” paleontologist and study co-author Grant Zazula tells Yukon News’ Jackie Hong.

The reality of the situation is more anti-climactic. “You have this animal that’s seven feet tall that just eats little pond weeds,” Zazula adds, “and you want it to be more dramatic than that, but it’s not.”

Yukon News' Hong reports that scientists believe the giant beaver migrated from what is now the continental United States to Canada and Alaska around 100,000 years ago. The species thrived in verdant mixed-conifer forests intermingled with plant-filled wetlands for many millennia, but began to suffer the ill effects of Earth’s drier climate beginning 25,000 years ago. At first, local populations vanished mainly from northern territories, but by 10,000 to 11,000 years ago—only one beaver enclave, found in the surrounding Great Lakes region—remained.

Writing for the Conversation, Plint explains that giant beavers—distinguished from their smaller modern counterparts by bulkier curved incisors and an elongated rather than paddle-shaped tail—failed to adapt to the continent’s changing climate largely because of their overdependence on wetland habitats.

Today, modern beavers, which actually co-existed alongside giant ones for tens of thousands of years, were able to use their sharp-edged teeth to cut down and eat trees, build lodges and dams, and essentially shape the landscape to suit their needs. Ancient mega-sized ones, however, found themselves ill-equipped to seek out new habitats and food sources.

“We didn't find any evidence that [giant beavers] were actually cutting down and eating trees,” Plint concludes to CBC News. “They weren't ecosystem engineers the same way that modern beavers are."

Meilan Solly | | READ MORE

Meilan Solly is Smithsonian magazine's senior associate digital editor, history.