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Why did giant beavers go extinct? It was their diet, researchers say

New research suggests that unlike their smaller modern cousins, giant beavers didn't eat wood — and that may be why they didn't survive beyond the last ice age.

The massive rodents didn't survive beyond the last ice age, 10,000 years ago

Researcher Tessa Plint with a life-sized statue of a giant beaver, at the Beringia Interpretive Centre in Whitehorse. (Western University)

If a modern beaver can fell big trees, dam rivers and essentially create its own habitat — imagine what a two-metre-tall giant beaver with 15-centimetre incisors could have done?

Yukon paleontologist Grant Zazula suggests the difference might be like comparing "a chainsaw and an industrial logging operation."

But new research suggests the giant beaver didn't actually do much logging — and that may be why it didn't survive beyond the last ice age.

"We actually found out that the giant beavers were eating a diet of aquatic plants. So we didn't find any evidence that they were actually cutting down and eating trees," said Tessa Plint, co-author of the new study from Western University, published in the journal Scientific Reports. 

The researchers say giant beavers thrived in wetlands where they mostly ate aquatic plants. (Western University)

"They weren't ecosystem engineers the same way that modern beavers are."

The researchers studied giant beaver bones and teeth found near Old Crow, Yukon, in the 1970s. Analysing the isotopic signatures of the fossils helped them determine what the animals ate.

It turns out that the massive rodent, which could weigh more than 100 kilograms, mostly ate aquatic plants — and so was dependant on wetland habitat.

"And that made them very, very susceptible to climate change, especially as the climate got warmer and drier towards the end of the last ice age," Plint said.

Beavers versus Bieber. Giant beavers could be up to 6 feet tall, and weigh more than 100 kilograms. (Western University)

In other words, as wetlands dried up, giant beavers ran out of food. They once ranged over much of North America but were extinct by about 10,000 years ago.     

"They disappeared because there was no more pond weeds for them to eat," said Zazula.

Zazula says the new research helps add detail to what happened in Yukon during the last ice age, when there were periods of climate cooling and warming, and giant beavers, giant sloths and mastodons were eventually replaced by wooly mammoths, horses and bison.

Plint agrees, calling her research "another piece of the puzzle" in making sense of the ice age megafauna extinction.

A giant beaver skeleton at the Canadian Museum of Nature. (Canadian Museum of Nature)

She also suggests that modern beavers may have survived and thrived because they were better able to adapt compared to their larger cousins.

"We all know the modern beaver can dam up the river to build its own nice little pond to live in. And that's pretty handy when wetlands are starting to dry up and they're in short supply. So I think it probably did give it a bit of an advantage," Plint said.

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