| |
| Morphology |
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 "featherfoot"),
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).
Eared seals also
called "walking seals" are
made of sea lions and fur seals and
communicate by "barking."
They have large foreflippers compared
to earless seals and use them as their
main source of maneuverablity in the
water. They are also more agile on
land than earless seals. As their
name suggests, eared seals have external
ears. As a group, sea lions are larger
than fur seals. Fur seals have more
underfur. Some researchers contend
that dividing fur seals and sea lions
into the subfamilies Arctocephalinae
and Otariinae is unjustified, noting
that Northern fur seals and Cape fur
seals are more related to sea lions
than other fur seals.
The Walrus is the
sole member of its family. They are
easily recognized by their long tusks
and large bodies. They are more closely
related to eared seals than to earless
seals.
Earless seals, also
called “true seals,” lack
external ears. They have more developed
hind limbs and swim by powerful sideways
movements of these, yet are more cumbersome
on land than the eared seals. Earless
seals are better built for diving.
They are more streamlined than eared
seals, and can therefore swim more
effectively over long distances. However,
because they cannot turn their hind
flippers downward, they are very clumsy
on land, having to wriggle with their
front flippers and abdominal muscles;
this method of locomotion is called
galumphing. True seals do not communicate
by "barking" like eared
seals. They communicate by slapping
the water and grunting.
|
|
|
 |
| |
| Origin |
Seals evolved
from bearlike carnivores about 25 to 30 million
years ago. Early seal fossils are found in Europe’s
North Atlantic and Mediterranean regions. By 8
to 10 million years ago seals were well established
in the northern hemisphere—numerous seal
fossils have been discovered in the Chesapeake
Bay region of the United States dating from this
time period. Found with these fossils are giant
teeth resembling those of the great white shark,
perhaps then, as now, an important seal predator.
Scientists debate whether all
seals evolved from a single land ancestor, or
whether true seals developed independently of
the eared seals and the walrus. Recent molecular
evidence from deoxyribonucleic acid (DNA), the
genetic material found in all living organisms,
suggests that true seals, eared seals, and the
walrus are all more closely related to each other
than to any other mammal. This indicates they
all had the same land ancestor.
Seals moved into the southern
hemisphere only in the last few million years—long
after they had become common and diverse in the
north. In Antarctic waters, they evolved into
unique species such as the Weddell, crabeater,
and leopard seals.
The monk seals remained in the
tropics, perhaps lagging behind as their relatives
crossed the equator into southern latitudes. Scientists
consider the Hawaiian monk seal to be a living
fossil. While modern seals have fused tibia and
fibula bones in their flippers, the Hawaiian monk
seal still has separate tibia and fibula bones
in its hind flippers—a condition seen in
the earliest fossil seals. Even the structure
of the large vena cava blood vessel in the Hawaiian
monk seal resembles that of bears and dogs more
than that of other seals. |
|
|
| |
| Seals and the law |
Grey seals were protected as early as 1914 when the Grey Seals Protection Act made it unlawful to kill seals between 1 October and 15 December each year, and never at Haskeir in the Hebrides. The Act was originally intended to protect seals for five years until the population had begun to increase, but it was then extended. Common seals were not protected, and in the 1960s, between 1,000 and 1,200 were killed each year in Scotland. |
| |
|
|
 |
Details |
|
| |
|
