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Pinniped
From Wikipedia, the free encyclopedia
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Pinnipeds Fossil range:
Late Oligocene - Recent |
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Common Seal (Phoca
vitulina) |
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Scientific classification |
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Families |
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Odobenidae |
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).
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.
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
Reproduction
[[Media: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
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.
Wikipedia
http://en.wikipedia.org/w/index.php?title=Pinniped&action=history
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