Pinniped

Taxobox
name = Pinnipeds
fossil_range = Late Oligocene - Recent


image_width = 250px
image_caption = Common Seal ("Phoca vitulina")
regnum = Animalia
phylum = Chordata
subphylum = Vertebrata
classis = Mammalia
ordo = Carnivora
subordo = Caniformia
unranked_familia = Pinnipedia
unranked_familia_authority = Illiger, 1811
subdivision_ranks = Families
subdivision =
Odobenidae (walruses)
Otariidae (fur seals and sea lions)
Phocidae (true seals)

Pinnipeds ("fin-feet", lit. "winged feet") or fin-footed mammals are a widely distributed and diverse group of semi-aquatic marine mammals comprising the families Odobenidae (walruses), Otariidae (eared seals, including sea lions and fur seals), and Phocidae (earless seals). Formerly classified as a separate biological suborder, "Pinnipedia" is now sometimes considered a superfamily within Caniformia, a suborder in the Carnivora order.

Evolution

Recent molecular evidence suggests that pinnipeds evolved from a bearlike ancestor about 23 million years ago during the late Oligocene or early Miocene epochs, a transitional period between the warmer Paleogene and cooler Neogene period. [cite journal
author=John J. Flynn et al
title=Molecular Phylogeny of the Carnivora
journal=Systematic Biology
year=2005
volume=54
pages=317 – 337
url=http://home.uchicago.edu/~johnf/pdf/Flynn_etal_2005.pdf
format=dead link|date=June 2008 – ^{[http://scholar.google.co.uk/scholar?hl=en&lr=&q=intitle%3AMolecular+Phylogeny+of+the+Carnivora&as_publication=Systematic+Biology&as_ylo=2005&as_yhi=2005&btnG=Search Scholar search]} ] The earliest fossil pinniped that has been found is "Enaliarctos", which lived 24 – 22 million years ago. 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. There has been longstanding debate as to whether walruses diverged from a common otariid-phocid ancestor, or whether the phocids diverged before a common otariid-odobenid ancestor. The most recent evidence suggest that the latter hypothesis is more likely. [cite journal
author=Ulfur Arnason , Anette Gullberg, Axel Janke, et al
title=Pinniped phylogeny and a new hypothesis for their origin and dispersal
journal=Molecular Phylogenetics and Evolution
year=2006
volume=41
pages=345–354
doi=10.1016/j.ympev.2006.05.022]

Overview

s).

Otariidae

Eared seals, also called "walking seals" and "otariids", include the animals commonly known as sea lions and fur seals. These are vocal, social animals that are somewhat better adapted to terrestrial habitats with rear flippers that can turn forward such that they can move on all fours on land. Their foreflippers are larger than those of earless seals and are used as a primary source of maneuverability in the water. Eared seals have external ears, as their name suggests, and more dog-like snouts, further distinguishing them from the true seals. While sea lions are generally larger than fur seals and lack the dense underfur of the latter, the long-standing division into subfamilies ("Arctocephalinae" and "Otariinae" for fur seals and sea lions respectively) has been shown to be unjustified in light of recent genetic evidence suggesting that several fur seal species are more closely related to some sea lions than other fur seals. The iconic ball-balancing circus seal is generally some species of sea lion, most commonly a California sea lion.

Phocidae

Earless seals, also called “true seals" or "phocids" are the most diverse and widespread of the pinnipeds. They lack external ears, have more streamlined snouts and are generally more aquatically adapted. They swim with efficient undulating whole body movements using their more developed rear flippers. The efficiency of their swimming and an array of other physiological adaptations make them better built for deep and long diving and long distance migrations. They are, however, very cumbersome on land, moving by wriggling their front flippers and abdominal muscles. True seals generally communicate by slapping the water and grunting, rather than vocalizing.

Odobenidae

The walrus is an exclusively Arctic species - the sole surviving member of the once diverse and widespread "Odobenidae" family. They are easily recognized by their long tusks and great bulk (up to 2000 kg). While they share with otariids the ability to turn their rear flippers forward, their swimming is more reminiscent of that of true seals, relying more on sinuous whole body movements. They also lack external ears. Unlike eared seals and true seals, which feed primarily by hunting fish and squid in the water column, walrus generally prefer benthic invertebrates, in particular clams. It is the development of the unique squirt and suck method of feeding on molluscs that differentiated the original walrus ancestor from the other pinniped lineages. There remains debate as to whether the walrus diverged from the eared seals before or after the true seals.

Adaptations

Flippers

Pinnipeds have proportionally 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 that are found either on the front flippers (earless seals) or back flippers (eared seals). Because water has a much higher density than air, their flippers can be much smaller proportionately in relation to their size than the wings of a bird or bat. Additionally, pinnipeds are essentially weightless in the water, allowing them to come to a standstill, and perform aquabatic feats in water that would be impossible for atmospheric flying creatures.

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 normal rate. 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. [ [http://encarta.msn.com/encyclopedia_761564979/Seal_(mammal).html Encarta article on Seals] ]

Warmth

To keep warm in cold waters, pinnipeds have a layer of blubber under their skin, providing buoyancy, and caloric energy. Newborn pinnipeds have no blubber.

Molting

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 molting.

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.

Feeding

consumes molluscan prey items by sucking the soft parts from the shell.

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 as 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, Common seal pups and birds.

Almost all pinnipeds are potential prey for orcas and larger sharks. Arctic species are an important component of polar bear diet.

Reproduction

Males of many species, (e.g. elephant seals, South American sea lions and Northern fur seals) aggressively defend groups of specific females, referred to as harems. Males of other species (e.g. most sea lions and Cape fur seals) defend territories on reproductive rookeries while females move freely between them. Some form of competition, either for females or territories, some of which can be violent, is an integral part of the male breeding strategy among most pinnipeds. Otariids, which are generally more land-adapted, tend to form major aggregations in the summer months on beaches or rocky outcrops. Consequently, their reproductive behavior is easier to observe and well studied. Walruses and many phocids, on the other hand, tend to form smaller aggregations, often in remote locations or on ice, and copulate in the water. Their reproductive behavior is therefore generally less well known.

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, otariid feeding grounds are generally closer to shore and females go on foraging trips. Fat content of otariid milk is lower than that of the phocids, owing to the protracted lactation period (typically 25–50%). Protracted nursing also leads to the formation of social bonds.

Taxonomy

* Family Odobenidae
** Walrus, "Odobenus rosmarus"
**"Imagotaria downsi" (extinct)
* Family Otariidae
** "Genus Arctocephalus"
*** Antarctic Fur Seal, "A. gazella"
*** Guadalupe Fur Seal, "A. townsendi"
*** Juan Fernandez Fur Seal, "A. philippii"
*** Galapagos Fur Seal, "A. galapagoensis"
*** Brown Fur Seal, "A. pusillus"
****South African Fur Seal, "A. pusillus pusillus"
****Australian Fur Seal, "A. pusillus doriferus"
*** New Zealand Fur Seal, "A. forsteri"
*** Subantarctic Fur Seal, "A. tropicalis"
*** South American Fur Seal, "A. australis"
** "Genus Callorhinus"
*** Northern Fur Seal, "C. ursinus"
** "Genus Eumetopias"
*** Steller Sea Lion, "E. jubatus"
** "Genus Neophoca"
*** Australian Sea Lion, "N. cinerea"
** "Genus Otaria"
*** South American Sea Lion, "O. flavescens"
** "Genus Phocarctos"
*** New Zealand Sea Lion, "P. hookeri"
** "Genus Zalophus"
*** California Sea Lion, "Z. californianus"
*** Japanese Sea Lion, "Z. japonicus" - extinct (1950s)
*** Galapagos Sea Lion, "Z. wollebaeki"
* Family Phocidae
** Subfamily Monachinae
*** Tribe Monachini
**** "Monachopsis" (extinct)
**** "Pristiphoca" (extinct)
**** "Properiptychus" (extinct)
**** "Messiphoca" (extinct)
**** "Mesotaria" (extinct)
**** "Callophoca" (extinct)
**** "Pliophoca" (extinct)
**** "Pontophoca" (extinct)
**** Hawaiian Monk Seal, "Monachus schauinslandi"
**** Mediterranean Monk Seal, "Monachus monachus"
**** Caribbean Monk Seal, "Monachus tropicalis" (probably extinct around 1950)
*** Tribe Miroungini
**** Northern Elephant Seal, "Mirounga angustirostris"
**** Southern Elephant Seal, "Mirounga leonina"
*** Tribe Lobodontini
**** "Monotherium wymani" (extinct)
**** Ross Seal, "Ommatophoca rossi"
**** Crabeater Seal, "Lobodon carcinophagus"
**** Leopard Seal, "Hydrurga leptonyx"
**** Weddell Seal, "Leptonychotes weddellii"
*** Swan-necked Seal, "Acrophoca longirostris" (extinct)
*** "Piscophoca pacifica" (extinct)
*** "Homiphoca capensis" (extinct)
** Subfamily Phocinae
*** "Kawas benegasorum" (extinct)
*** "Leptophoca lenis" (extinct)
*** "Preapusa" (extinct)
*** "Cryptophoca" (extinct)
*** Bearded Seal, "Erignathus barbatus"
*** Hooded Seal, "Cystophora cristata"
*** Tribe Phocini
**** Common Seal or Harbor Seal, "Phoca vitulina"
**** Spotted Seal or Larga Seal, "Phoca largha"
**** Ringed Seal, "Pusa hispida" (formerly "Phoca hispida")
**** Nerpa or Baikal Seal, "Pusa sibirica" (formerly "Phoca sibirica")
**** Caspian Seal, "Pusa caspica" (formerly "Phoca caspica")
**** Harp Seal, "Pagophilus groenlandica" (formerly "Phoca groenlandicus")
**** Ribbon Seal, "Histriophoca fasciata" (formerly "Phoca fasciata")
**** "Phocanella" (extinct)
**** "Platyphoca" (extinct)
**** "Gryphoca" (extinct)
**** Gray Seal, "Halichoerus grypus"

In culture

Seals, sea lions, and walruses 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"
* 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
* Sparky, an escaped seal in the episode "Love and Sandy" from the 1964 television series "Flipper"
* An unnamed robotic seal in Sonic the Hedgehog 2 (8-bit), who serves as the boss of the Aqua Lake Zone.
* A Pokémon creature Seel
* Wolfgang the Seal, former charcter from Sesame Street.

Because of the creature's name being coincidentally spelled the same as the unrelated word "seal" for a stamp, the confusion of one with the other is an occasional comic gag, as in "Christmas seal", or the live seal produced by Harpo Marx in "Horse Feathers" when Groucho Marx tries to find the legal seal for a contract document.

Notable fictional walruses include:
* Chumley, the walrus sidekick to Tennessee Tuxedo (the Penguin) [http://www.toontracker.com/totaltv/tennesse.htm]

At least three professional sports teams in the San Francisco, California, area have been known as the "Seals".

See also

* Cetaceans
* Sirenia
* Seal (disambiguation)
* Nothosaur
* Vocal learning

References