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Pinnipeds (Pinnipedia) are a group of semi-aquatic marine mammals that include sea lions, fur seals, true seals and the walrus. Members of this group are also known as the fin-footed mammals and are characterized by clumsiness on land but great agility in the water.

Pinnipeds are well suited for life in aquatic habitats. They have a streamlined, barrel-shaped body. They have powerful, broad flippers and can dive to depths of more than 330 feet.

They range in size from the 150-pound, 4-foot long Baikal seal (the smallest pinniped) to the 8,800-pound, 13-foot long southern elephant seal (decidedly the largest pinniped).

Pinnipeds have a number of adaptations for heat regulation. Species that inhabit cold water environments have blubber that insulates their internal organs. In addition to providing insulation, blubber also offers pinnipeds the benefit of buoyancy. Blood flow to the flippers is restricted to minimize heat loss. Additionally many pinnipeds can constrict the blood vessels near the surface of their skin and in doing so also reduce heat loss. When basking in the warm sunlight, they can dilate the blood vessels in the skin to absorb heat.

Pinnipeds that inhabit warmer regions cool by resting on land either in the shade or in tidal pools. They might flip sand over their body, in a similar way elephants dust themselves with dirt.

The eyes of pinnipeds are well-suited for seeing both under water as well as in open air. A clear membrane covers the eye underwater to protect it from sea water and debris.

Pinnipeds can hold their breath for long periods of time underwater. Some species can go for almost two hours without having to resurface for another gulp of air.

When diving, their heart rate slows and their blood flow is restricted to extremities, so that their organs receive the blood they need.

Pinnipeds fall prey to predators such as sharks, orcas and polar bears. Pinnipeds that inhabit the Antarctic face no threat from land predators.

Some pinnipeds form harems or rookeries when breeding. Some species compete for females or defend territories through aggressive battles.

Pinnipeds are carnivores. They feed on fish, and a variety of other marine life including shellfish, squid, penguins and a variety of marine invertebrates.

Pinnipeds have a worldwide distribution. They inhabit temperate and polar seas.


Pinnipeds are classified within the following taxonomic hierarchy:

Animals > Chordates > Vertebrates > Tetrapods > Amniotes > Mammals > Pinnipeds

Pinnipeds are divided into the following taxonomic groups:

  • True seals (Phocidae) - Also known as earless seals, are the most diverse of all pinniped groups. They include monk seals, ross seals, leopard seals, bearded seals, hooded seals, common seals, harp seals, grey seals and numerous other species. True seals are well-adapted for diving and can swim underwater for long periods of time. They are agile swimmers and move efficiently and quickly underwater. They use their front flippers mostly for steering and their back flippers for propulsion forward.
  • Eared seals (Otariidae) include 16 species. This group is also known as the sea lions or fur seals. Eared seals are social mammals and are more agile on land than the true seals. Their rear flippers can be oriented forward enabling them to crawl on all four limbs when on land. Eared seals are well suited for cold waters and climes. They have both blubber and a fur coat. Many species have been hunted to extinction for their coats which are prized for their great capacity for insulation.
  • The walrus (Odobenus rosmarus) is the only living member of its family. Walruses are large pinnipeds that inhabit a circumpolar region the Northern Hemisphere. Their range is discontinuous and includes portions of the Arctic Ocean and sub-Arctic seas. Walruses are easily recognized by their prominent tusks. They have long whiskers and are very large and bulky in build. Despite their impressive size, they are still smaller than two species of elephant seals.