Like their larger whale relatives, dolphins were
once land-based mammals. Living in the sea meant changing
over time almost every part of their body. For example,
the nostrils moved to the top of the head and they
develped an organ, the fatty tissue or melon, for
navigation and finding prey underwater by transmitting
sound waves.
One of the most obvious adaptations is the
dolphin's body shape. The animals have a very streamlined
body, similar to that of sharks and other large fish,
which moves quickly and easily through the water. In
fact, dolphins are such efficient swimmers that submarine
designers have modeled new vessels on their
bodies.
The skin of a dolphin is smooth for streamlining
and feels like rubber. Droplets of oil released from
living cells under the skin's suface further help the
animal to glide through the water by reducing friction.
As in the whale's body, there is a layer of fat or
blubber that keeps the animal warm. Blubber also helps
the dolphin stay afloat, as fat is lighter than
water.
Some dolphins have been trained to dive to more
than nine hundred feet, although they don't usually dive
so deeply. To this, the animal's body adjusts to
increasing water pressure by collapsing its lungs through
its specially hinged ribs and decreasing its heart rate so
that blood goes to the brain and heart first, before
organs such as the intestine and liver.
