Size
In general, bottlenose dolphins are 2 to 3.9 m (6.6 to 12.8 ft.). Their average weight is 150 to 200 kg (331.5 to 442 lbs.).
Maximum length and weight reported in the wild was from an individual in the Eastern North Atlantic that measured 4.1 m (13.5 ft.) and 650 kg (1,400 lbs.).
- A wild individual from the Western North Atlantic weighed 284 kg (626 lbs.).
The average adult length of dolphins in Alliance of Marine Mammal Parks and Aquariums facilities is 2.59 m (8.5 ft.). The average adult length in the wild is 2.2 to 2.7 m (7.2 to 8.9 ft.).
Coastal bottlenose dolphins measured off Sarasota, Florida average 2.5 to 2.7 m (8.2 to 8.9 ft.) and weigh between 190 and 260 kg (419 to 573 lbs.).
Large bottlenose dolphins in the Pacific may be 3.7 m (12 ft.) and weigh 454 kg (1,000 lbs.). In the Mediterranean, bottlenose dolphins can grow to 3.7 m (12 ft.) or more.
Body Shape
A bottlenose dolphin has a sleek, streamlined, fusiform body.
Skin
Bottlenose dolphins have a few, sparse hair follicles around the tip of their rostrum, though any individual hairs that are present fall out before or shortly after birth.
Dolphin skin is highly specialized and plays an important role in hydrodynamics. Upon close observation, cutaneous ridges may be seen on the surface of a dolphin’s skin that run circumferentially around the body trunk and vary in direction past the dorsal fin and other isolated areas. Cutaneous ridges may play an important role in sensory function
and in drag reduction as a dolphin swims.
A dolphin’s skin is smooth and feels rubbery. The skin has no hair or sweat glands. The outer skin layer (epidermis) is about 15 to 20 times thicker than the epidermis of humans.
Dolphin skin constantly flakes and peels as new skin cells replace old cells. A bottlenose dolphin's outermost skin layer may be replaced every 2 hours. This sloughing rate is 9 times faster than in humans. This turnover rate ensures a smooth body surface and probably helps increase swimming efficiency by reducing drag (resistance to movement).
A bottlenose dolphin's skin color is gray to dark gray on its back, fading to white on its lower jaw and belly.
- 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 sea surface.
- Some bottlenose dolphins show spots on their bellies or light streaks along their sides. Many populations of Indo-Pacific bottlenose dolphins are ventrally spotted.
The skin layer beneath the epidermis is the dermis. The dermis contains blood vessels, nerves, and connective tissue.
A dolphin's blubber (hypodermis) lies beneath the dermis. Blubber is a layer of fat reinforced by fibrous connective tissue.
- Blubber contributes to a dolphin's streamlined shape, which helps increase swimming efficiency.
- Blubber stores calories, which provide energy when food is in short supply.
- Blubber reduces heat loss, which is important for thermoregulation.
- Blubber providing a measure of protection from predation, as predators must bite through this layer to reach vital organs. Shark bite scars are not uncommon on wild bottlenose dolphins.
- Blubber thickness fluctuates by season as well as with body size and health status.
Pectoral Flippers
A dolphin's forelimbs are pectoral flippers. Pectoral flippers have the major skeletal elements of land mammal forelimbs, but they are foreshortened and modified. The skeletal elements are rigidly supported by connective tissue.
Pectoral flippers are curved back slightly and pointed at the tips.
Pectoral flipper length averages 30 to 50 cm (11.7 to 19.5 in.).
Dolphins use their pectoral flippers mainly to steer and, with the help of the flukes, to stop.
Blood circulation in the flippers adjusts to help maintain body temperature.
- 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.
- To shed excess body heat, circulation increases in veins near the surface of the flippers and decreases in veins returning to the body core.
Flukes
Each lobe of a dolphin's tail is called a fluke. Flukes are flattened pads of tough, dense, fibrous connective tissue, completely without bone, cartilage, or muscle.
From tip to tip, an adult's flukes measure about 60 cm (23.4 in.) across. Fluke spread is about 20% of the total body length.
Longitudinal muscles of the back and peduncle (tail stock) move the flukes up and down to propel a dolphin through water.
Like the arteries of the flippers, the arteries of the flukes are surrounded by veins to help conserve body heat in cold water.
Dorsal Fin
A bottlenose dolphin's dorsal fin is often falcate (curved back), although the shape is quite variable. It is located at the center of the back.
Like the flukes, the dorsal fin is made of dense, fibrous connective tissue, with no bone, cartilage, or muscle.
As in the flukes and the flippers, arteries in the dorsal fin are surrounded by veins to help conserve or dissipate body heat.
The dorsal fin may also help maintain balance as a dolphin swims, but is not necessarily essential. In fact, some whales and porpoises don’t have dorsal fins at all.
The dolphin's dorsal fin contains no bone, cartilage, or muscle. The shape varies among individuals but it is usually falcate.T
Head
The rounded region of a dolphin's forehead is called the melon. The melon contains fat and plays an important role in dolphin echolocation.
A bottlenose dolphin has a well-defined rostrum (snout-like projection) in front of the melon. The rostrum is typically 7 to 8 cm (3 in.) long, marked by a lateral crease.
Teeth are conical and interlocking.
- Teeth are designed for grasping (not chewing) food.
- Bottlenose dolphins have 18 to 26 teeth on each side of the upper and lower jaws, a total of 72 to 104 teeth.
- A tooth's diameter measures about 1 cm (0.4 in.).
- Dolphin teeth are not replaced.
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, jelly-like mucus that lubricates the eyes, washes away debris, and probably helps streamline a dolphin's eye as it swims. This tear-like film may also protect the eyes from ineffective organisms.
- A dolphin's eyes may move independently of each other.
Ears, located just behind the eyes, are small inconspicuous openings, with no external pinnae (flaps).
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.
- The blowhole is relaxed in a closed position. To open the blowhole, the dolphin contracts the muscular flap.
