The Order Pinnipedia
  Seals, sea lions and walrus
Pinnipeds are flesh-eating mammals with streamlined, torpedo-shaped bodies, limbs modified into flippers, and webbed feet - adaptations for life in the water. A thick layer of oily fat, or blubber, under the skin insulates them against the cold. They are closely related to the carnivores, from which they probably evolved about 30 million years ago. There are three families.
Family Odobenidae
There is one species: walrus Odobenus rosmarus: found in Arctic waters. Like the eared seals, the walrus can turn its hind flippers forwards to aid movement on land; but unlike them it has no external ears. The upper canines of the adult male grow downwards to form tusks up to 27 in. long.
Family Otariidae
Sea lions or eared seals: 13 species
Unlike the walrus, the eared seals have conspicuous external ears; they can use all four limbs when moving on land. The family is divided into two groups, sea lions and fur seals.

Family Phocidae
Earless or true seals: 18 species
The true seals, which may have evolved from the same stock as did the otter (other pinnipeds may have evolved from a bear-like ancestor), have no obvious external ears, and their hind limbs or flippers cannot be swung forwards for moving on land.

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