Pinniped
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 Common Seal (Phoca vitulina)
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Pinnipeds ("fin-feet", lit. "winged feet") are large 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).
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[edit] Information
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).
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.
[edit] Families
Pinnipedia (pi-ni-peed' e-a) (L. pinna, feather, + ped, foot) currently has three identified families:
- Odobenidae (walruses): contains 1 species in 1 genus
- Otariidae (sea lions, eared seals, and fur seals): contains 12 species in 6 genera
- Phocidae (true-earless-seals): contains 19 species in 13 genera
[edit] 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). Because of these constraints, pinnipeds mate and give birth with a high level of reproductive synchrony. The most synchronous species are the two phocids (seals)—the harp and hooded seals—in which all females are estimated to become sexually receptive during a period of 10–15 days. Males compete for females at rookeries. Females are usually highly clustered here to reduce the level of male harassment, particularly by low-ranking males. Females compete for central positions and call out if attacked by subordinate males that are subsequently chased away by the dominant bull. In general male otarids (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 in the otarids.
[edit] 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.
[edit] See also
[edit] References
- ^ John J. Flynn et al (2005). "Molecular Phylogeny of the Carnivora". Systematic Biology 54: 317–337.
