Dolphins Physical Characteristics

A. Size.

1. Bottlenose dolphins measured off Sarasota, Florida averaged 2.5 to 2.7 m (8.2-8.9 ft.) and weighed between 190 and 260 kg (419-573 lb.) (Read, et al., 1993).
   
2. Differences in body size and skull dimensions may be related to habitat differences. The two northwestern Atlantic ecotypes exhibit a pronounced size variance (Herse and Duffield, 1990).
   
   a) In the northwestern Atlantic, small body size is characteristic of the coastal ecotype.
   
   b) Large body size is characteristic of the offshore ecotype.
   
3. Large bottlenose dolphins in the Pacific may be 3.7 m (12 ft.) and weigh 454 kg (1,000 lb.). In the Mediterranean, bottlenose grow to 3.7 m (12 ft.) or more.
   
4. On average, full-grown males are slightly longer than females, and considerably heavier. As juveniles, however, females grow at a faster rate until about 10 years of age (Read, et al., 1993).
   
   

B. Body shape.

A bottlenose dolphin has a sleek, streamlined, fusiform body.

C. Coloration.

1. Coloration is a nondescript gray to gray-green or gray-brown on the back, fading to white on the belly, lower jaw, and anal regions. The belly may be pinkish.
   
2. This coloration, a type of camouflage known as countershading, may help conceal a dolphin from predators and prey. When viewed from above, a dolphin's dark back surface blends with the dark depths. When seen from below, a dolphin's lighter belly blends with the bright surface of the sea.
   
3. Older animals in some regions sometimes show an inconspicuous spotting along their sides and on their bellies.

D. Pectoral flippers.

1. A dolphin's forelimbs are pectoral flippers. Pectoral flippers have all the skeletal elements of the forelimbs of terrestrial mammals, but they're foreshortened and modified.
   
2. The skeletal elements are rigidly supported by connective tissue. Thick cartilage pads lie lengthwise between the bones.
   
3. Pectoral flippers are curved slightly and pointed at the tips.
   
4. Dolphins use their pectoral flippers mainly to steer and, with the help of the flukes, to stop.
   
5. Blood circulation in the flippers adjusts to help maintain body temperature.
   
   a) Arteries in the flippers are surrounded by veins. Thus, some heat from the blood traveling through the arteries is transferred to the venous blood rather than the environment. This countercurrent heat exchange aids dolphins in conserving body heat.
   
   b) To shed excess body heat, circulation increases in veins near the surface of the flippers and decreases in veins returning to the body core (Ridgway, 1972).

E. Flukes.

1. Each lobe of the tail is called a fluke.
   
2. Flukes are flattened pads of tough, dense, fibrous connective tissue, completely without bone or muscle.
   
3. Longitudinal muscles of the back and caudal peduncle (tail stalk) move flukes up and down to propel a dolphin through water.Dolphins propel themselves forward by moving their flukes up and down.
   
4. The total spread of the flukes is about 20% of the total body length.
   
5. Like the arteries of the flippers, the arteries of the flukes are surrounded by veins to help conserve body heat in cold water.

F. Dorsal fin.

1. Like the flukes, the dorsal fin is made of dense, fibrous connective tissue, with no bones.
   
2. 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.)
   
3. As in the flukes and the flippers, arteries in the dorsal fin are surrounded by veins to help conserve body heat in cold water.
   
4. The dorsal fin is often falcate (curved back), although the shape is quite variable. It is located at the center of the back.

H Head.

1. A bottlenose dolphin has a well-defined rostrum (snoutlike projection), usually about 7-8 cm (3 in.) long, marked by a lateral crease.
   
2. Teeth are conical and interlocking.
   
   a) They are designed for grasping (not chewing) food.
   
   b) The number of teeth varies considerably among individuals. Most individuals have 20 to 25 teeth on each side of the upper jaw and 18 to 24 teeth on each side of the lower jaw, a total of 76 to 98 teeth (Rommel, 1990). A bottlenose dolphin may have as many as 98 conical teeth.
   
3. Eyes are on the sides of the head, near the corners of the mouth. See also eyesight.
   
   Glands at the inner corners of the eye sockets secrete an oily, jellylike mucus that lubricates the eyes, washes away debris, and probably helps streamline a dolphin's eye as it swims. This tearlike film may also protect the eyes from infective organisms (Young and Dawson, 1992).
   
4. Ears, located just behind the eyes, are small inconspicuous openings, with no external pinnae (flaps).
   
5. A single blowhole, located on the dorsal surface of the head, is covered by a muscular flap. The flap provides a water-tight seal (Ridgway, 1972).
   
   a) A bottlenose dolphin breathes through its blowhole.
   
   b) The bottlenose is relaxed in a closed position. To open the blowhole, a bottlenose dolphin contracts the muscular flap.

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