Giant beavers as tall as the average adult man once made their homes in wetlands all across North America.
But, toward the end of the last Ice Age, they began to disappear.
Unlike their modern and much smaller descendants, the 220-pound (100 kilograms) beasts did not eat wood, and instead chowed down on aquatic plants.
A new study has found that this restrictive diet may have directly played into their demise; as the Ice Age ended and the glaciers retreated, the wetlands dried up and their source of food dwindled.
By the end, giant beavers that made up the genus Castorides could only be found around the Great Lakes region around 11,000 to 10,000 years ago, according to researchers from Western University.
In their prime, however, the enormous spanned the entire continent. Fossil bones and teeth have been found everywhere from Florida to Alaska and the Yukon Territory.
But, they were nothing like the beavers we know today.
‘We did not find any evidence that the giant beaver cut down trees or ate trees for food,’ said Tessa Plint, who conducted the research while a graduate student at WU.
‘Giant beavers were not “ecosystem-engineers” the way that the North American beaver is.’
These creatures thrived in mixed-conifer forests that hosted wetlands, where they had plenty of access to submerged plants.
Researchers determined their diet by analyzing stable isotopes in their bones and teeth.
‘Basically, the isotopic signature of the food you eat becomes incorporated into your tissues,’ Plint said.
‘Because the isotopic ratios remain stable even after the death of the organism, we can look at the isotopic signature of fossil material and extract information about what that animal was eating, even if that animal lived tens of thousands of years ago.’
Though the wood-carving abilities of their modern descendants may have helped them make it through the changes, these ancient plant-eaters didn’t have the skill.
‘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,’ says Fred Longstaffe, Western’s Canada Research Chair in Stable Isotope Science.
‘Giant beavers couldn’t do this. 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 new findings on their diet help to solve one of many mysteries surrounding the demise of the megafauna after the Ice Age.
But, Plint says, ‘This is just one small piece of the Ice Age extinction puzzle.’