Tiny Beavers, Giant Beavers: One Happy Prehistoric Family

June 17, 2008 -- The world's smallest prehistoric beaver was the size of a tiny mouse but directly related to an 8-foot-long, 480-pound Ice Age giant, suggests a new study of fossils found in the American Midwest.

Much of the beaver family tree's bizarre history played out at the Valentine Formation in northern Nebraska, where paleontologist William Korth has studied the skeletons of big and little beavers that lived as long as 23 million years ago.

"The world's tiniest beaver turns out to have been related to the world's largest," Korth, of the Rochester Institute of Vertebrate Paleontology, told Discovery News.

He came to that conclusion after recently identifying the most primitive member of a beaver subfamily -- technically called a "tribe"-- known as the Nothodipoidini. Members of this now-extinct branch on the beaver family tree tended to be on the small side, but their huge front teeth often dwarfed the rest of the body.

Such was the case for the newly identified beaver Temperocastor valentinensis, which had large, fast-growing incisors that Korth says are "typical of tooth-digging rodents."

The findings are published in the latest issue of the journal Acta Paleontologica Polonica.

Today's beavers "do it all" by digging, swimming, cutting wood with their teeth and building dams. Their ancient relatives, however, seemed to be divided up into those that were digging and burrowing specialists and those that spent more of their time swimming and munching vegetation.