Dolphin Characteristics

Size and Body Shape
The average dolphin measures 8 to 13 feet and weighs between 419 to 573 pounds. 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. A bottle-nose dolphin has a sleek, streamline, fusiform body.

dolphin anatomy

Coloration and Skin
Bottle-nose dolphin's coloration is a non-descript 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. 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 viewed from below, a dolphin's lighter belly blends with the bright surface of the sea. Older animals in some regions sometimes show an inconspicuous spotting along their sides and on their bellies. A bottle-nose dolphin's skin is extremely delicate and easily injured by rough surfaces, making it very similar to human skin. Dolphin sheds its outer layer of skin about every two hours.


Pectoral flippers
A dolphin's forelimbs are pectoral flippers, which have all the skeletal elements of the forelimbs of terrestrial mammals, but they're foreshortened and modified. The skeletal elements are rigidly supported by connective tissue. Thick cartilage pads lie lengthwise between the bones. Pectoral flippers are curved slightly and pointed at the tips. Dolphins use their pectoral flippers mainly to steer and, with the help of the flukes, to stop.


Flukes
Each lobe of the tail is called a fluke. Flukes are flattened pads of tough, dense, fibrous connective tissue, completely without bone or muscle. 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.


Dorsal fin
Like flukes, the dorsal fin is made of dense, fibrous connective tissue, with no bones. 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. There are some dolphin species lack dorsal fins. The dorsal fin is often falcate (curved back), although the shape is quite variable. It is located at the center of the back.


Head of a Dolphin
A bottle-nose dolphin has a well-defined rostrum (snoutlike projection), usually about 3 inches long, marked by a lateral crease. Their teeth are conical and interlocking. They are designed for grasping (not chewing) food. 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. (See: Food.)

Eyes are on the sides of the head, near the corners of the mouth. 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. (See: Eyesight.)

Ears are located just behind the eyes, and are small inconspicuous openings, with no external pinnae (flaps). (See: Hearing.)

A single blowhole, located on the dorsal surface of the head, is covered by a muscular flap. The flap provides a water-tight seal. A bottlenose dolphin breathes through its blowhole. When the dolphin is relaxed the blowhole is in a closed position. To open the blowhole, the dolphin must contract the muscular flap. (See: Respiration.)

Dolphin Senses
    Hearing Dolphins have a well-developed, acute sense of hearing. The hearing range of a bottlenose dolphin respond to tones within the frequency range of 1 to 150 kHz. (The average hearing range for humans is about .02 to 17 kHz.) Unlike humans, a dolphin's inner ear is encased in a separate bone, called auditory bulla (earbone complex), which is connected to the skull with fibrous tissue. Thus, the bulla is essentially isolated from the skull, and sound enters the ear most efficiently through the jaw and middle ear.

    A fat-filled cavity in the lower jawbone appears to conduct sound waves through the jaw to bones in the middle ear. The specialized anatomy of the dolphin's ear probably allows it to localize sounds under water effectively, a task that is difficult for humans. A dolphin's middle ear cavity is filled with a highly vascularized (supplied with blood) tissue. When a dolphin dives, this tissue helps adjust pressure on the middle ear. As stated before a dolphin has small external ear openings, a few inches behind each eye. Each opening leads to a reduced ear canal and an eardrum.
    Eyesight Dolphins have acute vision both in and out of the water. A dolphin's eye is particularly adapted for seeing in water. In air, certain features of the lens and cornea correct for the refraction of light caused by the transition from aquatic to aerial vision. Without this adaptation, a dolphin would be nearsighted in air.

    The retinas of odontocetes have two central areas that receive images (human eyes only have one). Due to this feature of the retina, bottle-nose dolphins have binocular vision in air, and may have both binocular and monocular vision under water. A dolphin's retina contains both rod cells and cone cells, indicating that they may have the ability to see in both dim and bright light. (Rod cells respond to lower light levels than cone cells do.) The presence of cone cells suggests that dolphins may be able to see color, although studies have not actually determined this yet.

    Dolphin's eyes have a well-developed tapetum lacidum, a light-reflecting layer that reflects light through the retina a second time, giving them enhanced vision in dim light.
    Tactile A dolphin's skin appears to be sensitive to a broad range of tactile sensations. Dolphins are quite sensitive to touch, and spend a good deal of time touching and caressing each other. Free nerve endings are densely packed in the skin, especially around the snout, nipple, genital regions, and parts of the pectoral fin. These are all areas of frequent contact among dolphins. There sense of touch may enable dolphins to detect subtle differences in the water pressures surrounding their bodies. This would explain their ability to maneuver among obstacles with such grace and ease.
    Taste Bottle-nose dolphins do have taste buds, although they haven't been extensively studied. They are capable of detecting waterborne chemicals through their sense of taste.

    Researchers suggest that a dolphin might obtain information by tasting the trails of both urine and feces from other dolphins. These may contain sexual pheromones,indicating the sexual state and perhaps the identity of an individual. Tasting the trails may also enable dolphins to track companions over distances.

    Dolphins show strong preferences for certain species of food fishes. However, this may have more to do with the texture of the fish, rather than taste.
    Smell This is the only sense among dolphins that is lacking. Olfactory lobes of the brain and olfactory nerves are absent in all toothed whales, indicating that they have a limited sense of smell.
    (Dolphins--The Oracles of the Sea)

| Home | | Dolphin Evolution | | Bottle-nose Dolphins | | Dolphin Communication | | Aquatic Life |
| Intelligence and Human Interaction | | Dolphin Diet | | Continuing the Species | | Dolphin Behavior |
| Dolphin Longevity | | Dolphin Poem | | Pictures | | Fun Facts | | Endangered Dolphins | | E-mail |