Pinnipeds (from Latin pinna, "feather” or “wing," and pedis, "foot," meaning "winged feet" or "fin-feet") are large aquatic (mostly marine) mammals having both front and hind limbs in the form of flippers and comprising the taxonomic group Pinnipedia. Pinnipedia is usually considered a suborder of the order Carnivora, but is sometimes considered a separate order; more recently, Pinnipedia is regarded as a superfamily of the suborder Caniformia of Carnivora.
There are an estimated 50 million pinnipeds in the world; roughly 90 percent of them are phocid seals (Riedman 1990).
Among the pinnipeds, only phocids (true seals) live in the Antarctic and Arctic, while walruses inhabit the northern circumpolar waters; there are no otariids in the extreme polar regions (Riedman 1990).
Only two species of phocids are found in the tropics and these are small and endangered populations, but a number of fur seals and sea lions live in tropical and subtropical areas, with fur seals ranging widely into colder climates as well (Riedman 1990). All but two species of fur seals are found in the Southern Hemisphere, while sea lions are common to both hemispheres.
No pinnipeds are found in Asia (Riedman 1990).
Although fewer species of pinnipeds inhabit the Antarctic than the Arctic, the Antarctic seal populations are larger (including about 30 million or so crab-eater seals); in addition, the Antarctic seals also generally have larger bodies (Riedman 1990). The larger size may be an adaptation providing more insulation or may be related to more plentiful food supply.
Pinnipeds are typically sleek-bodied and rather large. Their bodies are well adapted to their aquatic habitat, in which they spend most of their lives. In place of hands, their forelimbs are large flippers (hence the name "fin-feet"), and their bodies narrow out into a tail.
The smallest pinniped, the Galapagos fur seal, weighs about 30 kg (66 lb) when full-grown and is 1.2 m (4 ft) long; the largest, the male southern elephant seal, is over 4 m (13 ft) long and weighs up to 2,200 kg (4,850 lb, more than 2 tons).
Pinnipeds are more streamlined, larger, and faster swimming than the sea otters, which have retained the front paws of a terrestrial carnivore, although their hind feet are flippers (Riedman 1990). All pinnipeds are carnivorous, eating fish, shellfish, squid, and other marine creatures. The leopard seal is probably the most carnivorous and predatory of all the pinnipeds, eating a wide variety of prey, from krill to penguins to other seals.