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Pinniped
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Pinnipeds (from Latin pinna, wing or fin, and ped-, foot) 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.
nt 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.
The earliest fossil pinniped that has been found is Enaliarctos, which lived 24 – 22 million years ago.
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Encyclopedia
Pinnipeds (from Latin pinna, wing or fin, and ped-, foot) 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.
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.
Overview
Pinnipeds are typically sleek-bodied, barrel-shaped, and can be rather large. Their bodies are well adapted to the aquatic habitat where they spend most of their lives. Their limbs have evolved into short, wide, flat flippers. The smallest pinniped, the Galápagos Fur Seal, weighs about 30 kg (65 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). In the Phocidae the two back flippers have evolved into a tail-like structure which can no longer be used for walking on land.
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 so 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 omids", 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. These mammals 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 mollusks 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, which have evolved into flippers. 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 flying creatures.
Oxygen conservation
Pinnipeds can conserve oxygen for long periods 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. Pinnipeds can hold their breath for nearly two hours underwater.
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 transmit them to the cochlea.
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. Additionally, the walrus 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 penguins 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 the 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 Brown 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
Image:Pinniped-phylogeny.gif|803px
rect 684 1 800 11 Canidae
rect 684 12 800 22 Ursidae
rect 684 23 800 33 Odobenus rosmarus
rect 684 34 800 44 Callorhinus ursinus
rect 684 45 800 55 Neophoca cinerea
rect 684 56 800 66 Otaria byronia
rect 684 67 800 77 Arctocephalus pusillus
rect 684 78 800 88 Phocarctos hookeri
rect 684 89 800 99 Arctocephalus forsteri
rect 230 191 300 202 Arctocephalus forsteri
rect 684 100 800 110 Arctocephalus australis
rect 230 203 300 213 Arctocephalus australis
rect 684 111 800 121 Arctocephalus galapagoensis
rect 230 214 300 224 Arctocephalus galapagoensis
rect 684 122 800 132 Arctocephalus gazella
rect 230 225 300 235 Arctocephalus gazella
rect 684 133 800 143 Arctocephalus tropicalis
rect 230 236 300 246 Arctocephalus tropicalis
rect 684 144 800 154 Arctocephalus philippii
rect 230 247 300 257 Arctocephalus philippii
rect 684 155 800 165 Arctocephalus townsendi
rect 230 258 300 268 Arctocephalus townsendi
rect 684 166 800 176 Eumetopias jubatus
rect 684 177 800 187 Zalophus californianus
rect 684 188 800 198 Erignathus barbatus
rect 684 199 800 209 Cystophora cristata
rect 684 210 800 220 Pusa hispida
rect 230 285 300 295 Pusa hispida
rect 684 221 800 231 Pusa sibirica
rect 230 296 300 306 Pusa sibirica
rect 684 232 800 242 Halichoerus grypus
rect 230 307 300 317 Halichoerus grypus
rect 684 243 800 253 Pusa caspica
rect 230 218 300 328 Pusa caspica
rect 684 254 800 264 Phoca largha
rect 230 269 300 339 Phoca largha
rect 684 265 800 275 Phoca vitulina
rect 230 280 300 350 Phoca vitulina
rect 684 276 800 286 Histriophoca fasciata
rect 684 287 800 297 Pagophilus groenlandicus
rect 684 298 800 308 Lobodon carcinophagus
rect 684 309 800 319 Ommatophoca rossii
rect 684 320 800 330 Hydrurga leptonyx
rect 684 331 800 341 Leptonychotes weddellii
rect 684 342 800 352 Mirounga angustirostris
rect 684 353 800 363 Mirounga leonina
rect 684 364 800 375 Monachus monachus
rect 684 376 800 387 Monachus schauinslandi
rect 684 388 800 398 Monachus tropicalis
desc none
Above: Phylogeny determined from parsimony analysis of 50 maximum likelihood gene trees
- Family Odobenidae
- Family Otariidae
- Genus Arctocephalus
- Antarctic Fur Seal, A. gazella
- Guadalupe Fur Seal, A. townsendi
- Juan Fernández Fur Seal, A. philippii
- Galápagos 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
- Genus Eumetopias
- Steller Sea Lion, E. jubatus
- Genus Neophoca
- Genus Otaria
- Genus Phocarctos
- Genus Zalophus
- 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
- Tribe Lobodontini
- 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)
- Baikal Seal or Nerpa, 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
See also
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