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- 12 December 2013 1:00 pm , Vol. 342 , #6164
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Giant Camels Roamed Arctic Realms
5 March 2013 12:00 pm
The long-lost cousins of today's camels once roamed the high Arctic, browsing open forests in regions that are near-barren landscapes today. That's the conclusion from an analysis of the fragmentary remains of an ancient leg bone unearthed on Canada's Ellesmere Island, which lies just west of northern Greenland. The find also adds to the tantalizing clues about how these moose-sized, presumably shaggy progenitors fit into the camel family tree—a lineage that today boasts only two species of true camels but includes plenty of South American relatives such as llamas, alpacas, guanacos, and vicuñas.
Today, camels inhabit arid regions stretching from northern Africa to the interior of Asia. But ancestors of the creatures first evolved in North America about 45 million years ago, says Natalia Rybczynski, a paleontologist at the Canadian Museum of Nature in Ottawa. Some of these animals crossed a land bridge from what is today Alaska to eastern Siberia—and that meant they were living, even thriving, at latitudes where few mammals can now subsist.
The fossils, dug up by Rybczynski and her colleagues in recent field seasons, came from a gravel-rich layer of sediments laid down more than 3.4 million years ago. The 30 or so bits of bone, none more than 7 centimeters long, have suffered much since they were entombed: Ice sheets have scoured Ellesmere Island several times in the past few million years, and today's freeze-thaw cycles continue to splinter fossils into ever-smaller fragments, Rybczynski says. The sizes and shapes of the bone bits suggest that they came from a tibia (a lower leg bone), but from those clues alone it's impossible to identify the species or group of mammal the fossils came from. However, some bone features clearly indicate that the creature was an artiodactyl, a broad group that today includes deer, cows, and camels.
Detailed comparisons of the collagen proteins trapped and preserved within the bone fragments to those produced by 37 living mammal species indicate that the ancient creature was most closely related to today's dromedary camel (the species with one hump), the researchers report online today in Nature Communications.
The new findings are "pretty exciting," says Grant Zazula, a paleontologist with the Government of Yukon in Whitehorse, Canada. "It's amazing to be able to get collagen out of fossils that are 3.5 million years old." The remarkable preservation, Rybczynski says, likely stems from a coating of iron minerals that helped seal the bones, as well as the natural cold-storage available in the Arctic.
Considering the proportions of the bone fragments, the camel was a giant, probably about 2.7 meters tall at the shoulder—almost 30% larger than its modern relatives are. The moose-sized mammal likely tipped the scales at 900 kilograms at the end of the summer browsing season but then slimmed down as it drew on fat reserves in its hump to sustain itself through the harsh Arctic winter.
The Ellesmere Island site is about 1200 kilometers farther north than any previous camel find, Rybczynski says. Fossils unearthed at a location about 10 kilometers away from the camel find, and from rocks of approximately the same age, reveal that the landscape hosted an open forest punctuated with peatlands and inhabited by bears, rabbits, beavers, a greyhound-sized deerlet, and a pony-sized, three-toed horse. Annual average temperature in the area was about -1.4°C, barely below freezing but still about 18°C warmer than the modern average.
The new findings indicate that the high Arctic, including Ellesmere Island in northeastern Canada and the land bridge that connected Alaska to northeastern Asia, was no evolutionary backwater. "The Bering land bridge wasn't just a temporary stop on the way to and from Asia," Zazula says. "It was a center of evolution."
Most of the protocamels that lived at lower latitudes in North America had teeth with high crowns suitable for grazing, says Mary Dawson, a paleontologist at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, who was not involved with the work. But giant camels that roamed the Yukon about 3.5 million years ago—and presumably their slightly larger relatives living on Ellesmere Island at the same time—had low-crowned teeth best suited for grinding foliage, as today's camels do. "These new findings tell us a lot," she notes. "They open up the Arctic as a place of origin for the camels of today."