About Dolphins
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Dolphins
are aquatic mammals which are closely
related to whales
and porpoises. There are almost forty species of dolphin in seventeen
genera. They vary in size from 1.2 metres (4 ft) and 40 kilograms (88
lb) (Maui's Dolphin), up to 9.5 m (30 ft) and ten tonnes (the Orca or
Killer Whale). They are found worldwide, mostly in
the shallower seas of the
continental shelves, and are carnivores, mostly eating fish and squid.
The family Delphinidae is the largest in the Cetacea, and relatively
recent: dolphins evolved about ten million years ago, during the
Miocene. Dolphins
are considered to be amongst the
most intelligent of
animals and their often friendly appearance and seemingly playful
attitude have made them popular in human culture.
Dolphins have a streamlined fusiform body, adapted
for fast
swimming. The basic colouration patterns are shades of grey with a
light underside and a distinct dark cape on the back. It is often
combined with lines and patches of different hue and contrast. The
head contains the melon, a round organ used for
echolocation. In many species, the jaws are elongated, forming a
distinct beak; for some species like the Bottlenose, there is a curved
mouth which looks like a fixed smile. Teeth
can be
very numerous (up to two hundred and fifty) in
several species. The dolphin brain is large and has a highly structured
cortex, which often is referred to in discussions about their advanced
intelligence. Unlike most mammals, dolphins do not
have hair, but
they are
born with a few hairs around the tip of their rostrum which they lose
after some time, in some cases even before they are born. The only
exception to this is the Boto river dolphin, which does have some small
hairs on the rostrum. There are more about dolphins... Dolphins
are often regarded as
one of Earth's most
intelligent
animals, though it is hard to say just how intelligent dolphins are, as
comparisons of species' relative intelligence are complicated by
differences in sensory apparatus, response modes, and nature of
cognition. Furthermore, the difficulty and
expense of doing
experimental work with large aquatics means that some tests which could
meaningfully be done still have not been carried out, or have been
carried out with inadequate sample size and methodology. Dolphin
behaviour has been studied extensively by humans however, both in
captivity and in the wild.
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