The chameleons

are a family of lizards renowned for several unusual features. The body is high in proportion to the length and is flattened from side to side. The toes of each foot are joined, three on the inside of the front feet and on the outside of the hindfeet, resulting in tong-like feet that allow for a powerful grip on a perch. Most species have a prehensile tail, usually held in a tight coil when not being used to grip a perch.

Above all, however, chameleons are distinguished from other lizards by three specific characteristics: its ability to change color, eyes set in turrets that can move independently of each other, and a highly extensible tongue which can be shot out at speed to a length greater than the chameleon's head and body.

Color-Changing Ability

Although other reptiles, as well as many fish and squid, can change color, the chameleon is recognized as the "quick change artist" of the animal world. A popular story relates how a chameleon changed its color to red when placed on a red cloth and to green when placed on a green cloth, but almost had a stroke when placed on a cloth with a plaid pattern. The truth is not quite so dramatic, however. Most species of chameleon have a basic color and pattern that suits their particular habitat and do not really change color to resemble the background, but rather in response to light intensity, temperature, and/or emotional state. An angry chameleon, for example, goes black with rage.

The Mechanics of Color Change

Specialized color cells lie under the transparent upper layer of skin in four layers. The outermost is made up of xanthophores (yellow-bearers) and erythrophores (red-bearers). Under this layer are two reflecting layers, one reflecting blue light, the other white light. Beneath this is a layer of melanophores. These contain a dark brown pigment called melanin, the same substance that colors human skin brown or black. The main body of each melanophore lies under the reflecting layers but it sends tentacle-like arms up through the other layers.

To alter the skin color, the color cells alter in size, so that by variation of the amounts of yellow, red and dark brown, different colors are produced by mixing. When the blue reflecting layer is under yellow cells, green is produced and where the blue layer is missing, light reflected from the white layers enhances the yellow or red coloration. The melanophores control the shading of the colors. Bright colors result when all the melanin is concentrated in the main bodies of the melanophores. If the melanin spreads along the arms enough to obscure the white layer, greens and reds become darker. If the melanin is dispersed completely, the chameleon becomes dark brown.

"Shooting Tongue"

Although chameleons eat the same kinds of food as other lizards (insects and other small invertebrates), how they catch their prey is unique. Chameleons capture prey by shooting out their long tongue, trapping the victim on the tip and carrying it back to the mouth. The capture happens so fast that only a high-speed camera can capture the movement. In the top photo at left, the chameleon is lining up on its target, a spider in the upper right corner. In the middle photo, the tongue has shot out to its fullest extent. The bottom photo shows the tongue being retracted, minus the spider. The spider had to be extremely quick to escape this chameleon, however, as studies have shown that a 5-1/2 inch tongue can be extended in 1/16 second and retracted in 1/4 second.

The ultra-fast movement of the chameleon's tongue is made possible by some very specialized mechanisms. At the back of the jaw lies a V-shaped bone called the hyoid. Attached to this bone by a flexible joint is the tongue bone, over which the tongue fits. When the chameleon is about to "shoot" the hyoid bone is moved forward slightly to push the tip of the tongue out of the mouth. Then, the circular muscles in the tip of the tongue contract violently so that the tongue is foced out, and simultaneously the hyoid bone is thrust further forward. Longitudinal muscles withdraw the tongue almost as quickly.

Distribution of Chameleons

Most of the 80 some species of chameleons live in Africa south of the Sahara, including the island of Madagascar. One species, the common chameleon, ranges from the Middle East along the coast of North Africa into southern Spain. Two others live in the southern end of the Arabian Peninsula, and a third lives in India and Sri Lanka.

Scientific Classification

phylum Chordata
subphylum Vertebrata
class Reptilia
order Squamata
suborder Iguania
family Chamaeleonidae
genera & species
Chamaeleo chamaeleon common chameleon
C. dilepis flap-necked chameleon
C. jacksonii Jackson's chameleon
C. oweni three-horned chameleon
Brookesia spp. stump-tailed chameleons