Polar bears are the largest land carnivores in the world, rivaled only by the Kodiak brown bears of southwestern Alaska. Polar bears sit at the top of the food chain in the biologically rich Arctic. The most carnivorous of the bear species, polar bears feed primarily on the fat of ice-dependent seals. The remains of these seals provide food for many other Arctic wildlife species, giving polar bears a vital role in their ecosystem.
Polar bears are marine mammals, and spend much of their time on Arctic sea ice. Many adaptations make polar bears uniquely suited to life in icy habitats. Their fur is thicker than any other bears’ and covers even their feet for warmth and traction on ice. A thick layer of blubber beneath their fur provides buoyancy and insulation. The long neck and narrow skull of the polar bear probably aid in streamlining the animal in the water while warming the air that they breathe, and their front feet are large, flat and oar-like, making them excellent swimmers.
http://www.defenders.org/polar-bear/basic-facts
