Size
Throughout their distribution, Commerson's dolphins average 120 to 170 cm (3.9-5.6 ft.) and weigh up to 86 kg (190 lbs.).
- In South American waters, the maximum length of males is about 144 cm (4.7 ft.) while females are 147 cm (4.8 ft.).
- The larger Kerguelen dolphin males may measure as much as 167 cm (5.5 ft.) long and females as much as 174 cm (5.7 ft.).
Mature females tend to grow slightly larger than males.
Body Shape
The general body shape of a Commerson's dolphin is roughly cylindrical but tapering at both ends. This characteristic fusiform shape is energy efficient for swimming. Compared to other body shapes, this body shape creates less drag (the opposing force an object generates as it travels through water). Their fusiform body shape and reduced limb size decrease the amount of surface area exposed to the external environment. This helps dolphins conserve body heat.
Coloration
The Commerson's black and white color pattern is a type of camouflage called disruptive coloration.
- Disruptive coloration is a pattern that obscures the outline of an animal by contradicting the animal's body shape.
- This color pattern may help conceal the small dolphin from prey or predators.
The Commerson's dolphin's color pattern also gives us a way to distinguish males and females. The male dolphin has an oval patch on its underside, while the female's patch is less regular and, in some cases, more V-shaped.
Kerguelen dolphins are black, white, and gray.
Pectoral Flippers
A Commerson's dolphin's forelimbs are adapted for swimming.
- As it swims, a dolphin uses its pectoral flippers to steer and, with the help of the flukes, to stop.
Pectoral flippers have the major skeletal elements of the forelimbs of land mammals, but they are shortened, modified, and rigidly supported by connective tissue.
The Commerson's dolphin's flippers have rounded tips.
Blood circulation in the pectoral flippers adjusts to help maintain body temperature. See Thermoregulation.
Flukes
Each lobe of the two-lobed tail is called a fluke. Flukes are flat pads of tough, dense, fibrous connective tissue, completely without bone or cartilage.
Longitudinal muscles of the back (both above and below the spine) and caudal peduncle (tail stock) move the flukes up and down. This motion moves the dolphin forward through water.
Like the arteries of the flippers, the arteries of the flukes are surrounded by veins to help maintain body temperature. See Thermoregulation.
Dorsal Fin
Like the flukes, the dorsal fin is made of dense, fibrous connective tissue, without bones or cartilage.
A Commerson's dolphin's dorsal fin is rounded.
As in the flukes and the flippers, arteries in the dorsal fin are surrounded by veins to help maintain body temperature. See Thermoregulation.
Like the keel of a boat, the dorsal fin may help stabilize a Commerson's dolphin as it swims at high speeds, but a fin is not essential to its balance.
Head
The Commerson's dolphin's rostrum resembles those of porpoises - short and blunt rather than long and beaklike like most dolphins.
A dolphin's 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 the eyes as a Commerson's dolphin swims. This tear like film may also protect the eyes from infective organisms.
Ears are small inconspicuous openings just behind each eye, with no external flaps or pinnae.
A single blowhole on top of the head is covered by a muscular flap.
- A Commerson's dolphin breaths through its blowhole.
- The blowhole is relaxed in a closed position, and the flap provides a water-tight seal. To open its blowhole, a Commerson's dolphin contracts the muscular flap.
Inside, the dolphin's mouth, small pointed teeth are adapted for grasping and tearing, not chewing, food.
- Most individuals have 29 to 30 teeth on each side of both jaws, a total of 116 to 120 teeth.
Skin
A Commerson's dolphin's black and white skin is smooth. The outer layer continually and rapidly renews itself, and the old skin sloughs off.
