Brown Bears Moved South Before Ice Age, Study Says
for National Geographic News
|November 11, 2004|
A fragment of a bear skull housed for several years in a Canadian museum may be rewriting the history of North America's brown bears.
Scientists say the skull, which was retrieved from a gravel pit in central Alberta in 1997, is at least 25,000 years old.
The finding suggests that brown bears, having crossed the Bering Strait from Asia, must have ventured south, deep into North America, far earlier than previously thought.
The discovery also sheds light on the ancestry of modern brown bears. A genetic analysis of the skull fragment indicates its owner was closely related to the brown bears that inhabit southern Canada and the northern United States today.
"It's like finding a missing piece of a puzzle," said Paul Matheus, a paleontologist at the Alaska Quaternary Center at the University of Alaska in Fairbanks. Matheus is the lead author of the report, which is described in this week's issue of the journal Science.
Based on the fossil record, researchers say brown bears migrated from Asia to the edge of North America between 50,000 and 100,000 years ago. However, ice sheets were believed to have prevented the predators from moving beyond Alaska and Yukon, then a part of Beringia. (A land bridge formed during the last ice age, Beringia joined Asia to Alaska and northwestern Canada.)
About 13,000 years ago, an ice-free corridor opened up, allowing brown bears to travel south. Until now, the oldest brown bear fossils in southern Canada and the northern United States were about 13,000 years old, an age paleontologists equated with the bears' arrival.
However, continental glaciers only blocked the route south between roughly 23,000 and 13,000 years ago.
"This has always been a mystery," Matheus said. "If brown bears came over to eastern Beringia at least 50,000 years ago, why didn't they go all the way down if there was no ice blocking their way?"
The new skull discovery suggests that brown bears actually did make that journey before the ice sheets arose.
Matheus found the specimen by chance two years ago while nosing around the Provincial Museum of Alberta in Edmonton. It was one of many fossils collected from gravel pits in the area by Jim Burns, a curator at the museum.
"I looked at a collection of bones older than 23,000 years and found the brown bear fossil," Matheus said. "I wondered, What is that doing in here? It shouldn't be here."
Radiocarbon dating indicated the bear was about 26,000 years old. "We had brown bears much further south much earlier than they should be," the paleontologist said.
One thing Matheus and his colleagues at England's Oxford University were unable to explain very well during an earlier study was the ancestry of modern brown bears in southern Canada and the northern United States. This discovery appears to solve that problem.
Genetic testing by scientists at Oxford and the Max Planck Institute in Germany showed that the Edmonton skull fossil belongs to the same genetic group as modern southern brown bears.
"It's a nice finding, because it filled in a gap in the records that was kind of puzzling," said Blaire Van Valkenburgh, a paleobiologist at the University of California at Los Angeles. "It makes more sense that the brown bears would have been south of the ice [25,000 years ago]."
"The results also indicate that the southern bears are very distinct from Alaskan bears," she added.
The new findings may also raise new questions about whenand howthe first humans migrated into the New World.
For decades many archaeologists have argued that humans migrated south of Beringia via an ice-free corridor about 13,000 years ago, when the ice sheets began to recede.
These scientists used the first appearance of certain animals, such as the brown bears, as a proxy indicator for when this corridor may have been available to humans.
"But our results show that brown bears were down further south much earlier, and that we just hadn't found the oldest fossils yet," Matheus said. "Archaeologists can no longer use brown bears as a test for when the first humans came south."
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