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.
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"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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