A beaver fossil from 28 million years ago was discovered in eastern Oregon. Researchers believe this ancient species was a forerunner of today's modern beavers.
Microtheriomys brevirhinus is the first ancient beaver found which is believed to be related to the modern-day animals. Researchers theorize the creature also was related to Asian beavers that crossed the Bering Strait, entering North America roughly seven million years before our own time. The extinct species was roughly half the size of its modern-day counterpart, called Castor.
The ancient beaver fossils, a skull and teeth, were found less than a mile away from the visitor center at John Day Fossil Beds National Monument in Kimberly, Ore. The modern version of the animal is seen on the official flag of the Beaver State.
This ancient species lived alongside other creatures, now extinct, such as saber-toothed tigers, three-toed horses, a rhinoceros with a pair of horns, and giant pigs.
"While there is relatively little castorid (beaver species) diversity today, 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," Samantha Hopkins, a paleontologist with the University of Oregon, said.
Fossils of Microtheriomys brevirhinus were found alongside those of 20 other extinct rodents, including a dwarf tree squirrel and pocket mouse. Dating was determined from layers of volcanic ash immediately above and below the geological finds. The age of each of those layers was measured through examination of radioactive isotopes in the material.
This ancient beaver walked the Earth roughly 35 million years ago during the Oligocene period, which began nearly 34 million years ago, and ended 11 million years before our time. It was during this time frame that Antarctica, heading south due to continental drift, first developed an ice cap.
The fossils had been pushed toward the surface by natural processes which are found in the region.
"We've got badlands exposures here. 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," Joshua Samuels, paleontologist for the John Day Fossil Beds National Monument, told the press.
Fossils from more than 100 species of mammal have been found at the monument in Oregon.
Analysis of the ancient beaver fossils and the other finds will be detailed in the quarterly Annals of Carnegie Museum.
Photo: Bill Damon | Flickr
