The
Bottlenose Dolphin is grey, varying from
dark grey at the top near the dorsal fin to very light grey and almost
white
or maybe even a pinkish colour at the underside. This makes it harder to see
both from above and below when swimming. The elongated upper and lower jaws
form what is called the rostrum, which gives the animal the name
bottlenose.
The real nose, however, is the blowhole
on top of its head, and the nasal septum is visible when the blowhole is
open. Its face shows a characteristic "smile". The "smile"
does not mean that it is happy; it is unable to move its jaw to any other
position.
Adults range in length from 2 to 4 metres (6 to 13 ft) and in weight from 150 to 650 kilograms
(330 to 1430 lb)<2>;
however, in most parts of the world, the adult''s length is about 2.5 m
(8 ft) and adult weight ranges from 200 to 300 kg (440 to
660 lb), with males being slightly longer and considerably heavier than
females, on average. The size of the dolphin appears to vary considerably with
habitat. Most research in this area has been restricted to the North
Atlantic Ocean, where researchers <3>
have identified two ecotypes. Those dolphins in warmer, shallower waters tend to
have a smaller body than their cousins in cooler pelagic waters. For example, a
survey of animals in the Moray Firth in Scotland,
the world''s northernmost resident population, recorded an average adult length
of just under 4 m (13 ft). This compares with a 2.5 m
(8 ft) average in a population of Florida.
Those in colder waters also have a fattier composition and blood more suited to
deep-diving.
The flukes (lobes of the tail)
and dorsal fin
are formed of dense connective tissue and don''t contain bones or
muscle. The animal propels itself forward by moving the flukes up and down. The
pectoral flippers (at the sides of the body) are for steering; they contain
bones clearly homologous to the forelimbs of land mammals
(from which dolphins and all other cetaceans
evolved some 50 million years ago). In fact, recently, a Bottlenose Dolphin was
discovered in Japan that has two additional pectoral fins, or "hind
legs," at the tail, appearing to be about the size of a human''s pair of
hands. <4>
Scientists believe that a mutation must have caused the ancient trait to
reassert itself.