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| Evolution |
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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 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, Common seal pups and
birds. |
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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] |
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| Seal Population |
When toxic materials are discharged into the sea, ocean currents can disperse them over huge areas. For example, radioactive chemicals from England have been traced in the seas to the north of Russia. Some of these toxins enter the food chain at the level of plankton, and pass upwards through shellfish, fish, and ultimately seals at the top of the chain. These toxins include lead, mercury, cadmium, strontium, PCBs, and the insecticide DDT, all of which have been found in seals.
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Details |
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