Marine Biology (2+1)

Locomotion

           Marine mammals have a streamlined shape for efficient movement through water. The lack of fur coat on several marine mammals is an important advantage to swimming; smooth skin creates less drag than fur does.

            Pinnipedia is a Latin word meaning "feather-footed" and refers to the flippers, which are shaped like wings or feathers. Although most of their lives are spent in the water, pinnipeds are also dependent on land for resting, giving birth, and breeding. Locomotion is one major difference between sea lions and seals. Sea lions use their forelimbs (hands) for locomotion on land and in the water. In the water, they use their forelimbs in a flapping manner similar to birds in flight. Seals use their hind limbs (feet) for swimming by undulating (moving from side to side) their hindquarters. On land, they move with vertical undulations of the trunk of the body.

            The hind limbs of sea otters are so much larger than the forelimbs that walking on land is clumsy and slow. Sea otters spend most of their time in the water floating on their backs and alternately pumping the hind flippers up and down. When a sea otter wants to swim faster it lies on its belly, undulating its entire body.

            When polar bears are on land, huge paws help distribute their weight while little hair on their footpads increase friction between their feet and the ice. Polar bears can stay in the water for a long time and swim very well with a stroke like a crawl, pulling themselves through the water with their front legs while their hind legs trail behind.