Basic anatomy of Cetaceans- Dolphins
A general description about anatomy of Cetaceans (Whales, Dolphins and Porpoises)
They may be the most beloved creatures in the world, certainly as far as wild
animals are concerned. And they have been for centuries, rhapsodized by the
great Greek philosopher Plutarch as unique animals who sought "friendship
for no advantage." Once seen as saviors of the seas who were said to
rescue drowning sailors, now dolphins are extolled as spiritual healers for
anyone lucky enough to swim and play with them.
Well, here's a nice image of a dolphin. It shows many of the major features that
one might expect to find in a dolphin, all the way from the rostrum to the flukes.
Let's start from the top and work our way down.
The bulbous part of the dolphin at the "forehead" is called the dolphin's melon,
and is used in focusing the dolphin's echolocation clicks.
What is often called the "beak" or "nose" of a dolphin is the dolphin's rostrum.
Of course, you can see the dolphin's eyes. The eyes of a dolphin are oriented almost
exactly opposite of each other, and give the dolphin almost full 360 degree vision and
a narrow lane of stereoscopic vision. The eyes can move independently of each other,
which means a dolphin can literally look at two different things at the same time.
The fin on the back of the dolphin is called the dorsal fin, which helps stabilize
the dolphin in the water. The flippers on both sides near the front, underside of the
dolphin are called the pectoral flippers, which are used in helping the dolphins steer
and stop. The key difference between a fin and a flipper is that a flipper has bones,
a fin doesn't.
And finally, the appendages at the tail of the dolphin are called the dolphin's
flukes. A dolphin's flukes serve many different purposes, the most important of which is
that it helps create hydrodynamic motion, the dolphin uses it to swim.
Dolphins also have a think layer of blubber which acts as insulation so the dolphin
does not lose too much heat. This mechanism for heat conservation is sometimes too effective
however. To prevent the dolphin from over heating, the flukes of the dolphin act as a radiator
by cooling the warm blood that passes through them.
They have excellent hearing, which compensates for a poor (or entirely lacking) sense of
smell, and for the uncertainties of visibility underwater; they have a high tolerance to
carbon dioxide, to help with lengthy dives, and are two or three times more efficient than
land mammals at using the oxygen in inhaled air; their rib cages are collapsible for deep
diving; and they have layers of insulating fat to keep them warm.
Cetaceans have shed most of the external traces of their terrestrial ancestry and are
supremely adapted to underwater life. Their body shape has become streamlined and they have
lost most of their body hair, to improve hydrodynamic efficiency; they have short stiff necks,
which are essential for swimming at high speed; their front limbs have turned into flippers
and their hind limbs have disappeared; they have muscular tails to provide a powerful means
of propulsion; and their nostrils have moved to the top of their head for easy breathing at
the surface.
Skin
The dolphin's smooth skin is constantly being sloughed off and replaced. It is sensitive to
touch and easily scarred. This 'scarring' is a useful aid to researchers in helping them to
identify individual animals.
Melon
This is the fatty, rounded section of a dolphin's forehead, and it's critical
to its extremely sensitive and complex use of echolocation. The melon acts as an
acoustical lens to focus sound waves into a beam that is projected in front of
the animal.
Blowhole
The blowhole serves as a dolphin's nostrils, allowing it to breathe while swimming
at top speed. To breathe while asleep, female dolphins lie on the water's surface
with their blowholes exposed to the air; males sleep just below the surface and rise
to breathe periodically as a reflex action.
Cape
The cape is a darker region on the back of many cetaceans (whales, dolphins and porpoises) around the dorsal fin.
Dorsal fin
A dolphin's dorsal fin is cartilage that can be as distinctive as a human's face
and is used by scientists to identify individuals. Dolphins that have dorsal fins -
not all do - seem to use them for stability. Bottlenose Dolphins have stream-lined
bodies and a rounded head with a distinctive beak. They have a tall, falcate
(sickle-shaped) dorsal fin and broad, slightly pointed flippers.
Dorsal ridge
The dorsal ridge is a raised line or hump on the back of a some whales (instead of a
dorsal fin). Gray whales don't have dorsal fins, but instead have 6 to 12 knuckles or
bumps along the dorsal ridge. The lack of dorsal fins on grays and true Arctic whales,
such as the Beluga and the Bowhead, is possibly an adaptation that enables them to swim
among the flow ice without risking damage. However, the gray whales swim farther north
only as the melting ice permits, waiting until after the ice is gone. Because of this
behavior, people look at changes in the Bering Sea ice maps to help them know when the
gray whales will return. Grays and the whales with dorsal fins usually don't swim as
far as Point Hope, AK until July!
Keel
The dorsal fin may act as a keel. It probably helps stabilize a dolphin as it swims,
but is not necessarily essential to a dolphin's balance. (Some dolphin species lack
dorsal fins.) Dorsal fin - acts as a keel giving some stability as it swims.
Fluke
A Dolphin's tail has 2 lobes called flukes. These flukes are flat, and made up of
fibrous tissue. There is no bone or muscle. The tail fluke is used for swimming by the
back muscles moving the fluke up and down.
Genital slit
The male has two slits at the bottom side of the body: one hiding the penis and
further behind one for the anus. The female has one genital slit, housing the vagina
and the anus. Coitus is preceded by lengthy foreplay; then the two animals arrange
belly to belly, the penis extends out of its slit and is inserted into the vagina.
The act lasts only 10-30 seconds, but is repeated numerous times, with several minutes
break in between. The gestation period is 12 months. The young are born in shallow
water, sometimes assisted by a "midwife" (which may be male). A single calf is born,
about 1 meter (3 feet) long at birth. To speed up the nursing process, the mother
can eject milk from her mammary glands. There are two slits, one on either side of
the genital slit, each housing one nipple. The calf is nursed for 12 to 18 months.
The young life closely with their mother for up to 6 years; the males are not
involved in the raising of their offspring. The females become sexually mature at
age 5-12, the males a bit later, at age 10-12.
Navel
Pectoral fins (Flippers)
The pectoral flippers are the dolphin's forelimbs. They resemble the forearm of
land mammals. The flippers are curved and pointed on the ends and have a primary
function of helping the dolphin to steer.
Eyes
Dolphins come equipped with elastic lenses on their eyes that expand and contract
to let them focus both above and below the water. And they have special glands that
protect their eyes from salt water.
Beak/ Snout/ Rostrum (Teeth)
A dolphin's Beak, snout or rostrum with teeths aren't used for chewing - it swallows
food whole - but they do help it grab prey. Some scientists also think the teeth are
spaced in such a way to help the dolphin analyze sound waves that bounce back to it from
an object.
Skeleton
The basic mammalian skeleton has undergone a number of specialized changes. The
forelimbs have been modified into flippers and the bones of the hind limbs have
disappeared altogether. The pelvic girdle remains as a mere vestige buried in the ventral
musculature. A large number of the dolphin's ribs are 'floating'. i.e. not attached to
the sternum or breastbone. Ribs that are attached are often jointed, enabling the rib cage
to collapse under the pressure of a deep dive, without being damaged. The skull has become
tilted upwards in line with the spinal column and the cervical (or neck) vertebrae have
become fused together in almost all species.
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Actual programs for adopt Dolphin or Whale
Would you like to adopt a whale or dolphin? Following are one or more dolphin and whale
adoption programs. Most provide a certificate, photo, chart, and quarterly newsletter.
Check out the following web sites and contact the organizations if there is one for more
information about the programs.
»The Whale and Dolphin Adoption Project«
»Delivery UK wide; The Adopt a Dolphin pack«
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