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| A comparison of anklebones from the giant beaver and the newly identified species, Microtheriomys articulaquaticus, at the same scale. Credit: Jonathan Calede / Ohio State University |
A new analysis of a beaver anklebone fossil found in Montana suggests the evolution of semi-aquatic beavers may have occurred at least 7 million years earlier than previously thought, and happened in North America rather than Eurasia.
In the study, Ohio State University evolutionary biologist Jonathan Calede describes the find as the oldest known amphibious beaver in the world and the oldest amphibious rodent in North America. He named the newly discovered species Microtheriomys articulaquaticus.
Calede’s findings resulted from comparing measurements of the new species’ anklebone to about 340 other rodent specimens to categorize how it moved around in its environment – which indicated this animal was a swimmer. The Montana-based bone was determined to be 30 million years old – the oldest previously identified semi-aquatic beaver lived in France 23 million years ago.
"Beavers and other rodents can tell us a lot about mammalian evolution," said Calede, an assistant professor of evolution, ecology and organismal biology at Ohio State’s Marion campus.














