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- Polar Bear Evolution

Polar Bear Evolution

Scientists believe that the polar bear is a descendant of the brown bear. It is thought to be the most recent of the eight bear species.

The polar bear probably first appeared during the mid-Pleistocene period, or roughly 100,000 to 250,000 years ago. The polar bears of that time period were much larger than they are today, as were many other species.

Scientists believe that the polar bear evolved from a group of brown bears that became isolated by glaciers in an area near Siberia. The stranded bears underwent a rapid series of evolutionary changes in order to survive on the ice.

Today's polar bear is superbly adapted to life in the Arctic.

Scientist Ian Stirling notes that today's brown bears come in a range of colors from dark to light. Those with light coats no doubt had an advantage in hunting seals, enabling the trait to be passed to future generations.

The polar bear's silhouette is markedly different from that of the brown bear: its body is more elongated and it lacks a shoulder hump. Instead of a dished face, it has a Roman profile.

The polar bear's sense of smell is much keener than that of the brown bear, as is its eyesight. The polar bear's hearing is excellent as well. These heightened senses are necessary for survival in the changing conditions of the Arctic.

The polar bear's teeth also differ from those of the brown bear, which lives on a largely vegetarian diet. The polar bear's cheek teeth are sharper, an adaptation that allows the bears to shear off chunks of meat. In addition, their canine teeth, used for seizing and holding prey, are longer, sharper, and more widely spaced.

Other adaptations include a longer neck, useful in keeping the polar bear's head above water when swimming; warm, thick fur; and huge paws, which help spread the bear's weight on thin ice and are useful in swimming.

While brown bears hibernate in winter, polar bears do not. During an Arctic winter, there is no shortage of food, as seals are still available. Pregnant female polar bears do den, however, as cubs require shelter until they are three or four months old.

Sources: "Habitat Conservation Strategy for Polar Bears in Alaska," U.S. Fish & Wildlife Service, 1995; Polar Bears by Ian Stirling (University of Michigan Press: Ann Arbor, Michigan 1988); Webster World Encyclopedia (Webster Publishing, 1999).

Additional german informations can be found here.

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