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.
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.
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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