Mar. 28, 2002 The evolution of brown bears may be better understood with help from the radiocarbon dating of bone specimens found in nearly pristine condition preserved in Alaska’s permafrost.
Ancient DNA studies conducted on these specimens are the subject of an article in the March 21 issue of the journal, "Science" titled, "Dynamics of Pleistocene Population Extinctions in Beringian Brown Bears." The co-author Paul Matheus, is a researcher with the University of Alaska Fairbanks in the Alaska Quaternary Center and the Institute of Arctic Biology. University of Oxford researchers worked with Matheus to conduct a multi-disciplinary study of brown bear evolution in Alaska and the Yukon Territory. They used DNA studies and knowledge of the ecology in the region to explore what happened to the brown bear over the past 50,000 years, which is the limit of radiocarbon dating. The dates show that brown bear lived in Alaska and the Yukon up to 35,000 years ago, but then went extinct and show up again at 21,000 years. However, the data indicates that bears prior to 35,000 years ago were of a different genetic stock than those that re-emigrated 21,000 years ago. The authors concluded that the second group did not evolve from the first group. Instead the younger group derived from a separate population of brown bear in Eurasia, indicating a new migration of bears. The same thing happened again sometime after 10,000 years ago, because the brown bear in this area are not the same genetically as the ones that lived here between 21,000-10,000 years ago.
"This is all kind of new and strange in terms of concepts of how ice age mammals moved and evolved and responded to climatic and environmental changes," said Matheus.
Researchers used stable isotope data to determine aspects of ancient brown bear diets and compared them to those of the extinct short-faced bear, which peak between 35-21,000 years ago. They also examined whether competition between the two would help explain the 14,000 year absence of the brown bear and the extinction of the short-faced bear around 21,000 years ago.
"We concluded that other factors probably were responsible, because the two bears were quite different ecologically," Matheus said.
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