A new beaver species that lived 28 million years ago has recently been discovered from fossils in eastern Oregon, and remarkably it may be related to the modern beaver, new research says.
It was one of 20 other rodent species recently described in the May 15 edition of the journal Annals of Carnegie Museum.
The fossilized beaver skull and teeth were unearthed within a mile of the visitor center at the John Day Fossil Beds National Monument, according to the monument's paleontologist, Joshua Samuels. And unlike other species of ancient beavers found at this site, this specimen, named Microtheriomys brevirhinus, appears related to the modern beaver.
Although, it's less than half the size of a modern beaver and related to beavers from Asia that crossed the Bering land bridge to North America about 7 million years ago, The Associated Press (AP) reports.
Using analyses of radioactive isotopes from layers of volcanic ash left behind in the ground, the researchers were able to determine the beaver's approximate age.
"We've got badlands exposures here," paleontologist Samantha Hopkins, from the University of Oregon, told the AP. "As they get wet, whenever it rains or snows and the temperature heats or cools, the claystone these things are in shrinks and swells. The bones are pushed out. The rock breaks apart. The fossils are exposed. This one just came out of the ground it was preserved in."
The beaver apparently roamed what is now the monument during the Oligocene period, about 30 million years after the dinosaurs, along with three-toed horses, a two-horned rhinos, giant pigs, sabertooths, rabbits and several species of dogs.
"While there is relatively little castorid (beaver species) diversity today," Samuels noted, "there are hundreds of species (many of which are really important members of their faunal communities) in the fossil record of the Northern Hemisphere, and a better understanding of their diversity and evolutionary relationships has a lot to tell us about processes driving mammalian evolution over the last 40 million years."
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