Ursus maritimus, the polar bear, is a specialized predator that (ignoring those that forage for garbage in towns and villages along the Arctic coast) hunts solely on sea ice. Several studies have concurred that polar bears are closely related to brown bears. However, there is substantial disagreement about when polar bears first evolved. Estimates range from 70,000 to 1 million years ago. A recent genetic analysis of material from a fossil first described two years ago narrows the range.
The new study suggests that polar bears evolved about 150,000 years ago. The fossil used for the assessment is a jawbone found in Norway's Svalbard archipelago. It was unearthed from rocks that are between 110 and 130 thousand years old, and is the oldest polar bear fossil found to date. Using material from a tooth, researchers reconstructed the bear's mitochondrial genome, and compared it with the mitochondrial genome of six other specimens, including modern polar and brown bears from Alaska.
The researchers note that the findings suggest that polar bears may have survived previous warm periods by retreating to higher latitudes, and may be able to do so again. Obviously, this means that the appropriate habitat must be preserved and made available to them.
The study can be found at http://www.pnas.org/content/107/11/5053.