|Scientific Name||(Ursus maritimus|
Polar Bears are bears native largely within the Arctic Circle encompassing the Arctic Ocean, its surrounding seas and surrounding land masses. Around the age of four or five the female polar bears can start having babies. They usually only have two cubs and they have these babies in a cave they've dug in a large snow drift. They stay there over winter and come out in spring with the babies.
Male polar bears may grow 10 feet tall and weigh over 1400 pounds. Females reach seven feet and weigh 650 pounds. In the wild polar bears live up to age 25. The babies are much smaller than human babies when they're born. They are the size of a rat and weigh little more than a pound. They can grow to full man size in a year if they have lots of food.
Taxonomy and evolution Edit
The bear family, Ursidae, is believed to have split off from other carnivorans about 38 million years ago. The Ursinae subfamily originated approximately 4.2 million years ago. According to both fossil and DNA evidence, the polar bear diverged from the brown bear, Ursus arctos, roughly 150,000 years ago. The oldest known polar bear fossil is a 130,000 to 110,000-year-old jaw bone, found on Prince Charles Foreland in 2004. Fossils show that between ten to twenty thousand years ago, the polar bear's molar teeth changed significantly from those of the brown bear. Polar bears are thought to have diverged from a population of brown bears that became isolated during a period of glaciation in the Pleistocene.
More recent genetic studies have shown that some clades of brown bear are more closely related to polar bears than to other brown bears, meaning that the polar bear is not a true species according to some species concepts. In addition, polar bears can breed with brown bears to produce fertile grizzly–polar bear hybrids, indicating that they have only recently diverged and are genetically similar. However, because neither species can survive long in the other's ecological niche, and because they have different morphology, metabolism, social and feeding behaviors, and other phenotypic characteristics, the two bears are generally classified as separate species.
When the polar bear was originally documented, two subspecies were identified: Ursus maritimus maritimus by Constantine J. Phipps in 1774, and Ursus maritimus marinus by Peter Simon Pallas in 1776. This distinction has since been invalidated.
One fossil subspecies has been identified. Ursus maritimus tyrannus—descended from Ursus arctos—became extinct during the Pleistocene. U.m. tyrannus was significantly larger than the living subspecies.