The dolphin's intelligence, playfulness, and friendliness, its built-in smile and merry-looking
eyes
have been a source of
interest and enchantment to human beings from earliest times.
Dolphins are fishlike in form, with streamlined, hairless bodies.
Their
powerful, horizontal flukes, or tail fins, drive them through or out of
the water, while their
refins and dorsal fin are used for
steering. Dolphins breathe air through a single, dorsal blowhole.
The dolphin's intelligence, playfulness, and friendliness, its built-in
smile and merry-looking eyes have
been a source of interest and
enchantment to human beings from earliest times; it is a common figure
in
mythology and literature and has been much depicted in art, especially in
the posture of its graceful,
arched, 30-ft (9-m) leap. Dolphins have long
been famous for riding the bows of ships,
and it is now known that they
also ride the bows of large whales.
Dolphins produce an enormous variety of sounds, up to frequencies ten
times those heard
by human beings. The sounds are apparently produced by a
complex of anatomical structures
including the blowhole with its air sacs
and valves. Each dolphin has a signature whistle with
which it identifies
itself; a calf soon learns to recognize its mother's whistle. Clicking and
rapid
creaking sounds are the basis of the echolocation mechanism (sonar)
with which the dolphin
gathers extremely precise information about the
size, location, and nature of surrounding objects.
Dolphins communicate by
means of a demonstrably descriptive language understood by more
than one
species, using all the sounds in their repertory. They are observed to
converse,
and it has been repeatedly shown that one animal can convey
instructions to another.
Porpoise, common name applied to for six species of aquatic mammals
in the order Cetacea,
which also includes whales and dolphins. Porpoises
are generally smaller than dolphins and
have rounded conical heads that
lack the dolphin's characteristic beak. Porpoises have
triangular rather
than hooked dorsal fins, and instead of vaulting completely out of the
water like dolphins do, they make wheel-like rolls, surfacing about four
times a minute to breathe.
