Pinnipeds (/ˈpɪnᵻˌpɛdz/), commonly referred to by the umbrella term "seals", are a clade of carnivorous, fin-footed, semiaquatic marine mammals. Although they may all be referred to as seals, only two families are officialy known as seals - the Fur Seals and True Seals while the others are known as Sea Lions and Walruses. Their closest living relatives are the Bears and the mustelids (weasels, raccoons, skunks and the Red Panda), having diverged 50 million years ago.

Several species exhibit sexual dimorphism. They have streamlined bodies and four limbs that are modified into flippers. Though not as fast in the water as dolphins, seals are more flexible and agile. Otariids use their front limbs primarily to propel themselves through the water, while phocids and walruses use their hind limbs. Otariids and walruses have hind limbs that can be pulled under the body and used as legs on land. By comparison, terrestrial locomotion by phocids is more cumbersome. Otariids have visible external ears, while phocids and walruses lack these. Pinnipeds have well-developed senses—their eyesight and hearing are adapted for both air and water, and they have an advanced tactile system in their whiskers or vibrissae. Some species are well adapted for diving to great depths. They have a layer of fat, or blubber, under the skin to keep warm in the cold water, and, other than the walrus, all species are covered in fur.

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