Beavers: Radical Rodents and Ecosystem Engineers

Beavers: Radical Rodents and Ecosystem Engineers — page 9
BEAVER TALES ANCIENT ANCESTORS Paleontologist Frederick C Kenyon stands beside the fossilized spiral-shaped burrow of an extinct beaver called Paleocastor in 1892 The site of this excavation is now part of Agate Fossil Beds National Monument in Nebraska ERWIN H BARBOUR MUSEUM DIRECTOR PAPERS ARCHIVES SPECIAL COLLECTIONS UNIVERSITY OF NEBRASKA-LINCOLN LIBRARIES THE BEAVER FAMILY got its start in North America about 37 million years ago Although there are only two beaver species alive today dozens of others have come and gone Some of these now-extinct beavers inhabited dry treeless grasslands Others were semi-aquatic like modern beavers Very few of them cut wood with their teeth or built dams Several years ago I visited the Canadian Museum of Nature to learn more about ancient beavers from Natalia Rybczynski She’s a paleobiologist a scientist who studies fossil plants and animals Natalia got her start in paleobiology when she was 16 in this same museum as part of a high school mentorship program One of the beavers Natalia studies is called Dipoides It lived in the Arctic millions of years ago when the climate was warmer and forests grew in the Far North Down in the museum’s storage rooms Natalia opened a cabinet and pulled out a drawer filled with fossilized Dipoides bones and teeth She and other researchers dug them up on Ellesmere Island which is only about 500 miles 804 kilometers from the North Pole They’ve also unearthed lots of sticks with Dipoides tooth marks on them During my visit she showed me some four-million-year-old sticks with gnawed ends the oldest beaver-cut wood ever found The largest beaver that roamed the earth was at least as big as a Saint Bernard dog Its scientific name is Castoroides but most people call it the giant beaver When Natalia handed me one of this beaver’s incisors I was surprised by its size and weight It was nearly 6 inches 15 centimeters long and as heavy as a brick That’s partly because tooth enamel is the hardest material in the body Natalia explained My favorite extinct castorid is Paleocastor These prairie-dog-sized beavers used their teeth and long claws to dig vertical shafts that spiraled 6 to 10 feet 2 to 3 meters down to their underground burrows Some of the diggings eventually filled with sand and solidified into trace fossils It’s hard to believe these rock-hard corkscrews were made by relatives of modern beavers but fossilized Paleocastor bones found inside them confirm their origins 8