Seal, Pinniped, Paradise Bay, West Antarctica, Antarctica, South Pole

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• published: 11 Jul 2013
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Pinnipeds, also known as fin-footed mammals (from Latin pinna, wing or fin, and ped-, foot), often generalized as seals (although this term excludes the walrus in everyday English), are a widely distributed and diverse group of fin-footed marine mammals which are semiaquatic comprising the families Odobenidae (whose only living member is the walrus), Otariidae (the eared seals; includes sea lions, and fur seals), and Phocidae (the earless seals). The family does not include cetaceans, otters, or sirenians. Pinnipeds belong to the order Carnivora and the suborder Caniformia (known as dog-like carnivorans). There are three extant families of pinnipeds: Otariidae, Odobenidae and Phocidae, the former two are grouped in the superfamily Otarioidea while the latter belongs to the superfamily Phocoidea. Members of Otariidae are known as eared seals due to the presence of external ear flaps or pinna. These animals rely on their well developed fore-flippers to propel themselves though the water. They can also turn their hind-flippers forward and "walk" on land. Eared seals are consist of two types, sea lions and fur seals. Sea lions are distinguished by their rounder snouts and shorter, rougher pelage; while fur seals have more pointed snouts, longer fore-flippers and thicker fur coats with includes an undercoat and guard hairs. The former also tend to be larger than the latter. Five genera and species of sea lion are known to exist while two genera and nine species of fur seal exist. While sea lions and fur seal have historically been considered separate subfamilies (Otariinae and Arctocephalinae respectively), a 2001 genetic study found that the northern fur seal is in fact more closely related to several sea lion species. This is supported by a 2006 molecular study which also found that the Australian and New Zealand sea lion are more closely related to Arctocephalus than to other sea lions. Odobenidae consist of only one living member, the walrus. This animal is easily distinguished from other pinnipeds by its large size, nearly hairless skin and long upper canines, known as tusks. Like eared seals, walruses are capable of turning their hind-flippers forwards and can walk on land. However when moving in water, the walrus relies on its hind-flippers for locomotion while its fore-flippers are used for steering. In addition walrus lack external ear flaps. The family Phocidae consists of the true or "earless" seals. These animals lack external ear flaps and incapable of turning their hind-flippers forward, which makes them more cumbersome on land. In water, true seals swim by moving their hind-flippers and lower body from side to side. A 2006 molecular study supports the division of earless seals into two monophyletic subfamilies: Monachinae which consists of the elephant seals, monk seals and lobodontine seals, and Phocinae which includes Pusa, Phoca, Histriophoca, Pagophilus, Erignathus and Cystophora. Pinniped limbs, or flippers, are proportionally shorter than those of most other mammals. Because the density of water is much higher than that of air, pinniped flippers can also be proportionally much smaller than the wings of birds or bats, relative to total body size. The digits of each limb are bound together by a web of skin (fingers and toes), and have claws on either their front flippers (earless seals), or their back flippers (eared seals). Fur seals have both blubber and a specially adapted fur coat, including outer guard hairs that repel water and a layer of insulating underfur. For this reason they were particularly prized by sealers. Many species were nearly hunted to extinction. For most pinniped species, molting is an annual process of replacing worn fur (and in some cases, skin) that temporarily grounds them. Molting can compromise thermoregulation, so some species, such as elephant seals, fast and remain onshore for a month or more. In many species, pups are born with a natal coat of a different length, texture and/or color than adults. This coat is adapted for the terrestrial, preweaning period, either a thick pelage to keep them warm in arctic environments, or a thin layer of fur to keep them cool on summer sands. During their first molt (about 11 days after birth for harp seals), the pups replace this with an adult coat better suited to life at sea. Until this age, pups risk hypothermia and drowning if they spend too much time in the ocean. Some pinnipeds can hold their breath for nearly two hours underwater by conserving oxygen. During long duration dives, the heart rate can be reduced to about one-tenth of its normal rate. The arteries vasoconstrict and the sense organs and nervous system are the only organs to receive normal blood flow.