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'Pinnipeds' ("fin-feet", lit. "winged feet") are marine mammals belonging to the former biological suborder Pinnipedia (sometimes now a superfamily) of the order Carnivora. The pinnipeds now fall within the suborder Caniformia and comprise the families Odobenidae (walruses), Otariidae (sea lions, eared seals, and fur seals), and Phocidae (true seals). Recent molecular analysis reveals that the closest living relatives of the pinnipeds are the bears, which was already suspected for some time.^[1] An alternative hypothesis held that pinnipeds are polyphyletic, with the true seals derived from otterlike creatures and the walruses and eared seals from bearlike creatures, but the aforementioned molecular study established that the pinnipeds are indeed monophyletic (derived from a common ancestor).
Pinnipeds apparently evolved from a bearlike ancestor about 23 million years ago, at the transition between the warmer Paleogene period and the cooler Neogene period. First true seals and then walruses branched off, forming new families.

Contents

Morphology

Adaptations

Flippers

Oxygen conservation

Warmth

Moulting

Other adaptations

Evolution

Feeding

Reproduction

Taxonomy

In culture

See also

References

Morphology

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 "featherfoot"), 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).
Eared seals also called "walking seals" are made of of sea lions and fur seals and communicate by "barking." They have large foreflippers compared to earless seals and use them as their main source of maneuverablity in the water. They are also more agile on land than earless seals. As their name suggests, eared seals have external ears. As a group, sea lions are larger than fur seals. Fur seals have more underfur. Some researchers contend that dividing fur seals and sea lions the subfamilies ''Arctocephalinae'' and ''Otariinae'' are unjustified, noting that Northern fur seals and Cape fur seals are more related to sea lions than other fur seals.
The Walrus is the sole member of its family. They are easily reconized by their long tusks and large bodies. They are more closely related to eared seals than to earless seals.
Earless seals, also called “true seals,” lack external ears. They have more developed hind limbs and swim by powerful sideways movements of these, yet are more cumbersome on land than the eared seals. Earless seals are better built for diving. They are more streamlined than eared seals, and can therefore swim more effectively over long distances. However, because they cannot turn their hind flippers downward, they are very clumsy on land, having to wriggle with their front flippers and abdominal muscles; this method of locomotion is called galumphing. True seals do not communicate by "barking" like eared seals. They communicate by slapping the water and grunting.

Adaptations

Flippers

Pinnipeds have shorter limbs than most other mammals. As noted above, their limbs have evolved into flippers with true seals having more developed hind flippers and eared seals having more developed fore flippers. The walrus is intermediate between the two. A pinniped’s fingers and toes are bound together by a web of skin . They also have claws are can either be in the on the front flippers (earless seals) or back flippers (eared seals). Pinnipeds can move weightlessly in the water and thus their flippers can be smaller in relation to their size than the wings of a bird or bat.

Oxygen conservation

Pinnipeds can conserve oxygen for long period of time underwater. When the animal starts diving its heart rate slows to about one-tenth of the norm. The arteries squeeze shut and the sense organs and nervous system are the only organs to continue to receive a normal flow of blood. Pinnipeds are able to resist more pain and fatigue caused by lactic acid accumulation than other mammals. However once they return to the water surface, they need time to recover and bring their body chemistry back to normal. ^[2]

Warmth

To keep warm in cold waters, pinnipeds have a layer of blubber under their skin (which also provides buoyancy). The thickness depends on the species. Their blubber can also provide food for the animal. Newborn pinnipeds have no blubber.
Some pinnipeds can also can get warm from their fur. The white coat of the infant harp seal, may trap the energy of sunlight as heat near the skin. As noted above, fur seal have underfur.

Moulting

Like other mammals, pinnipeds have to shed their fur once in a while. Eared seals shed more slowly than earless seals. Most earless seals spend time in the water while moulting.

Other adaptations

A pinniped’s eyes are well adapted for seeing both above and below the water. When diving the animal has a clear membrane that covers and protects its eyes. In addition, its nostrils close automatically. Testicles and mammary glands are located in slits under the skin to keep the pinniped’s streamlined shape. They also have whiskers to help navigate and sensors in their skull to absorb sounds underwater and trasmit them to the cochlea.

Evolution

Pinnipeds appear to have diverged from their bear-like ancestors during the Latest Oligocene. The earliest fossil pinniped that has been found is ''Enaliarctos'', which lived 24–22 million years ago, at the boundary between the Oligocene and Miocene periods. It is believed to have been a good swimmer, but to have been able to move on land as well as in water, more like an otter than like modern pinnipeds. DNA evidence suggests that all modern pinnipeds descend from a common ancestor that lived sometime in the earliest Miocene, possibly an ''Enaliarctos''-like mammal. ^[3]

Feeding

All pinnipeds are carnivorous, eating fish, shellfish, squid, and other marine creatures. Most are generalist feeders, but some are specialists. For example; Ross Seals and Southern elephant seals mainly feed on squid. Crabeater seals eat mostly krill and Ringed seals feed almost exclusively on crustaceans.
Some seals will even eat warm-blooded prey including other seals. The leopard seal, which is probably the most carnivorous and predatory of all the pinnipeds, will eat penguins and well as Crabeater and Ross Seals. The South American sea lion also eats penguin as well as flying seabirds and young South American fur seals. Steller sea lions have been recorded eating Northern fur seal pups and birds.

Reproduction

The pinnipeds come ashore to breed (haul-out), and this often necessitates travelling long distances from their feeding grounds to suitable mating grounds (either on land or ice). with a high level of reproductive synchrony. The most synchronous species are the two (sea lions) defend a territory, whereas phocids defend clusters of females. These strategies reflect the different levels of mobility on land between otarids and phocids. The former have opposable hind flippers that can be placed flat on the ground to aid locomotion. True seals, on the other hand, cannot do this and drag themselves along using only their front flippers.
Females have a postpartum oestrus allowing them to mate soon after giving birth. Subsequent implantation of the embryo is delayed (embryonic diapause) thus removing the need to come ashore (haul-out) twice, once to give birth and again later to mate. After giving birth mothers suckle their young for a variable length of time. Amongst the phocids, lactation varies from 4 to 50 days, whereas the otarids may lactate from 4 to 36 months. This reflects the fact that phocid feeding grounds tend to be a long way off-shore so lactation is associated with maternal fasting. To compensate for the short lactation period, the fat content of phocid milk is higher than in any other species of marine mammal (45–60% fat). After lactation most female phocids make extensive migratory movements to feeding grounds for intensive foraging to recoup depleted energy reserves. On the other hand, otarid feeding grounds are generally closer to shore and females go on foraging trips to maintain lactation. Fat content of otarid milk is lower than that of the phocids owing to the protracted lactatory period (typically 25–50%). Protracted nursing also leads to the formation of social bonds

Taxonomy

★ Family: Odobenidae

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★ Walrus, ''Odobenus rosmarus''

★ 'Family Otariidae'

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★ 'Subfamily Arctocephalinae: fur seals'

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★ Northern Fur Seal, ''Callorhinus ursinus''

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★ Antarctic Fur Seal, ''Arctocephalus gazella''

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★ Guadalupe Fur Seal, ''Arctocephalus townsendi''

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★ Juan Fernandez Fur Seal, ''Arctocephalus philippii''

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★ Galapagos Fur Seal, ''Arctocephalus galapagoensis''

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★ Cape Fur Seal, ''Arctocephalus pusillus''

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★ New Zealand Fur Seal or Southern Fur Seal, ''Arctocephalus forsteri''

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★ Subantarctic Fur Seal, ''Arctocephalus tropicalis''

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★ South American Fur Seal, ''Arctocephalus australis''

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★ 'Subfamily Otariinae: sea lions'

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★ Steller's Sea Lion, ''Eumetopias jubatus''

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★ California Sea Lion, ''Zalophus californianus''

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★ Japanese Sea Lion, ''Zalophus (californianus) japonicus'' - extinct (1950s)

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★ South American Sea Lion, ''Otaria flavescens''

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★ Australian Sea Lion, ''Neophoca cinerea''

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★ New Zealand Sea Lion, ''Phocarctos hookeri''

★ 'Family Phocidae'

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★ 'Subfamily Monachinae'

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★ 'Tribe Monachini'

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★ ''Monachopsis'' (extinct)

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★ ''Pristiphoca'' (extinct)

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★ ''Properiptychus'' (extinct)

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★ ''Messiphoca'' (extinct)

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★ ''Mesotaria'' (extinct)

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★ ''Callophoca'' (extinct)

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★ ''Pliophoca'' (extinct)

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★ ''Pontophoca'' (extinct)

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★ Hawaiian Monk Seal, ''Monachus schauinslandi''

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★ Mediterranean Monk Seal, ''Monachus monachus''

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★ Caribbean Monk Seal, ''Monachus tropicalis'' (probably extinct around 1950)

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★ 'Tribe Miroungini'

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★ Northern Elephant Seal, ''Mirounga angustirostris''

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★ Southern Elephant Seal, ''Mirounga leonina''

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★ 'Tribe Lobodontini'

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★ ''Monotherium wymani'' (extinct)

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★ Ross Seal, ''Ommatophoca rossi''

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★ Crabeater Seal, ''Lobodon carcinophagus''

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★ Leopard Seal, ''Hydrurga leptonyx''

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★ Weddell Seal, ''Leptonychotes weddellii''

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★ Swan-necked Seal, ''Acrophoca longirostris'' (extinct)

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★ ''Piscophoca pacifica'' (extinct)

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★ ''Homiphoca capensis'' (extinct)

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★ 'Subfamily Phocinae'

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★ ''Kawas benegasorum'' (extinct)

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★ ''Leptophoca lenis'' (extinct)

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★ ''Preapusa'' (extinct)

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★ ''Cryptophoca'' (extinct)

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★ Bearded Seal, ''Erignathus barbatus''

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★ Hooded Seal, ''Cystophora cristata''

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★ 'Tribe Phocini'

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★ Common Seal or Harbor Seal, ''Phoca vitulina''

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★ Spotted Seal or Larga Seal, ''Phoca largha''

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★ Ringed Seal, ''Pusa hispida'' (formerly ''Phoca hispida'')

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★ Nerpa or Baikal Seal, ''Pusa sibirica'' (formerly ''Phoca sibirica'')

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★ Caspian Seal, ''Pusa caspica'' (formerly ''Phoca caspica'')

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★ Harp Seal, ''Pagophilus groenlandica'' (formerly ''Phoca groenlandicus'')

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★ Ribbon Seal, ''Histriophoca fasciata'' (formerly ''Phoca fasciata'')

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★ ''Phocanella'' (extinct)

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★ ''Platyphoca'' (extinct)

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★ ''Gryphoca'' (extinct)

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★ Grey Seal, ''Halichoerus grypus''

In culture

:''See also Walruses in the media
Seals and sea lions are popular animals in the media. They are often portrayed balancing beach balls on their noses and clapping with their flippers.
Notable fictional seals include:

★ Lou Seal: mascot for the San Francisco Giants

★ Kotick: the main character in Rudyard Kipling's short story ''The White Seal'', later made into a cartoon by Chuck Jones

★ Salty a seal that appears in the Disney cartoons ''Pluto's Playmate'' and ''Mickey and the Seal'' and later in ''Mickey's Mouseworks'' and ''House of Mouse''.

★ The title character of ''Andre''

★ Slappy the sea lion from ''Slappy and the Stinkers''

★ Whiskers from ''Manta and Moray''

★ Esmeralda the sea lion from the Disney version of 20,000 Leagues Under the Sea

★ The San-X company characters Mamegoma

★ The main characters of

See also

★ Cetaceans

★ Sirenians

★ Seal (disambiguation)

★ Nothosaur
by Martha

References

1. Molecular Phylogeny of the Carnivora, John J. Flynn et al, , , Systematic Biology, 2005
2. Encarta article on Seals
3. Pinnipedimorpha – seals, walrusies, sealions, and other seal-like carnivores Mikko