Brown bear solves ice-age puzzle

Fossil fund proves south migration earlier than expected

26, 000-year-old fossil bear bones Paul Matheus
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26, 000-year-old fossil bear bones have helped rewrite the development and migration history of the American brown bear. Although bears migrated over the frozen Bering Strait from Asia to the American continent 50, 000 to 100, 000 years ago, researchers have assumed that glaciers have blocked the southward movement to around 13, 000 years ago. The bear fossil refutes this.

Paul Matheus, paleontologist, discovered the brown bear bones some two years ago in the holdings of the Provincial Museum of Alberta. They had been found in gravel strata near the Canadian city of Edmonton a few years earlier, dating back to before the last glaciation, more than 24, 000 years ago. Using the radiocarbon method, Matheus dated the bones and recorded an age of about 26, 000 years, a time when, according to previous assumptions, no brown bear had ever existed in southern Canada.

Glacier barrier hinders south migration

The ancestors of today's brown bears probably migrated from Asia to Alaska and Yukon, then Beringia, some 50, 000 to 100, 000 years ago. Numerous skeletal finds testify to this. The passage to the south was still free at that time, but was blocked by continental glaciers around 23, 000 years ago. Researchers have previously assumed that the brown bears in southern Canada and the area of ‚Äč‚Äčtoday's USA brown bear fossils appear only about 12, 000 to 13, 000 years ago.

"It has always been a mystery why the brown bears did not move further south if they really arrived in Beringia about 100, 000 years ago, because the way south was blocked only 23, 000 years ago, " explains Matheus. "The discovery of the Edmonton fossil now shows that the brown bears moved south much earlier than previously thought." The new finds and their consequences are described in an article in the journal Science.

Relationship with southern population

However, to prove the importance of the find, Matheus still needed information on the genetic identity of the fossil. Therefore, they took part scientists colleagues of the British Oxford University and the German Max Plack Institute, which sequenced the mitochondrial DNA of the fossil and thus the bears clearly one of the populations of the premature, but also the modern brown bears could assign. display

"So far, scientists have had difficulty explaining the origins of modern brown bears in the southern part of Alberta, British Columbia, Montana and Idaho, " explains Matheus. "These bears belong to a genetic population that has been extinct in North America for more than 35, 000 years." And, adds the researcher, whose genetic type did not exist in Beringia even after the glacier retreat some 13, 000 years ago.

The age and genetic identity of the bear fossil means that the Brown Bears made it far further south than they had previously thought, even before the end of the Ice Age, but also that the bears in the Edmonton region around 26, 000 years ago were very close relatives of today's southern bear population.

"It's like finding a missing piece of the puzzle or the proverbial missing link, " says Matheus. Your ancestors must have been trapped south of the glacier barrier during the last Ice Age, approximately 23, 000 to 13, 000 years ago, because Edmonton was covered in ice at that time. For the history of brown bears in North America, this means a complete shift in previous ideas

(University of Alaska, Fairbanks, 15.11.2004 - NPO)