Scientists have uncovered a fossilized jawbone from the sediments of an island in the Svalbard archipelago, a set of islands in the Arctic Ocean that lie approximately half-way between Norway and the North Pole. The jawbone shares a convincing resemblance to that of a polar bear. If it is indeed the remains of a polar bear, it represents the oldest known fossil record of the species.
The research team, lead by Professor Olafur Ingolfsson from the University of Iceland, estimates the age of the fossil is at least 100,000 years old. This means the polar bear, thought to be a recently evolved species, has a longer evolutionary past than previously suggested.
Polar bears share a recent common ancestor with brown bears, their closest relative. The two species are believed to have diverged during the Upper Pleistocene (126,000–10,000 years before present). During that period, a population of brown bears in the far north of their range is thought to have been isolated by glaciers. The population changed over time and individuals better adapted to the harsh polar environment survived and reproduced. Over many generations, the isolated brown bears had evolved into polar bears.
This narrative suggests how the changes progressed, but the details of polar bear evolution remain obscure because the fossil record is sparse when it comes to the polar bears of the past. This is in no small part due to their habitat. The remains of polar bears would likely be scavenged or sink to the bottom of the Arctic Ocean before they had a chance to become preserved in the ice. Despite the lack of fossil evidence showing the progression of brown bear to polar bear, genetic analysis of the two present day species has yielded solid evidence that they are closely related.
A study published in the Proceedings of the National Academy of Sciences details the research that led to this conclusion. Scientists from Penn State University, the University at Buffalo, the University of Oslo collaborated to analyze a rare pair of fossil—a jawbone and tooth from an ancient polar bear.
The fossils—the tooth and jawbone—were discovered in 2004 by an Icelandic geologist working in Norway's Svalbard archipelago. The find was unique—few polar bear fossils have been discovered and are believed to be rare.
"Because polar bears live on the ice, their dead remains fall to the bottom of the ocean or get scavenged. They don't get deposited in the sediments like other mammals," said Oystein Wiig, a co-author of the study from the University of Oslo's Natural History Museum.
Photo (top) © Dagsjo / iStockphoto. Photo (bottom) © Ólafur Ingólfsson / University of Iceland.
References
Lindqvist, C., Schuster, S., Sun, Y., Talbot, S., Qi, J., Ratan, A., Tomsho, L., Kasson, L., Zeyl, E., Aars, J., Miller, W., Ingolfsson, O., Bachmann, L., & Wiig, O. (2010). Complete mitochondrial genome of a Pleistocene jawbone unveils the origin of polar bear Proceedings of the National Academy of Sciences, 107 (11), 5053-5057 DOI: 10.1073/pnas.0914266107
Ingolfsson, Ó., and Wiig, Ø. (2009). Late Pleistocene fossil find in Svalbard: the oldest remains of a polar bear ( Phipps, 1744) ever discovered Polar Research, 28 (3), 455-462 DOI: 10.1111/j.1751-8369.2008.00087.x
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