Lizard

I

Introduction

Lizard, reptile with four sprawling limbs, a long tail, and dry scaly skin without heavy, bony armor. Lizards are the largest living group of reptiles, with thousands of species that differ in size and shape. Most lizards are small; the largest is the Komodo dragon, which can reach 3 m (10 ft) in length. Lizards are closely related to snakes and a group of animals called amphisbaenians (see Worm Lizard). Most lizards eat insects and other small invertebrates. They are cold-blooded and can survive in dry, hot regions better than most other animals.

II

Physical Characteristics

Lizards typically have a rounded skull, a short neck, a flexible spine, short sprawling legs, and a long tail. This primitive four-legged body plan was common in many extinct groups of amphibians and reptiles, and has also been retained in living salamanders and tuataras, and in somewhat modified form in crocodilians.

Although lizards may resemble salamanders and some other amphibians, they differ in that lizards have dry scaly skin, and most have clawed feet. Unlike tuataras and snakes, most lizards have external ear openings. Lizards also are distinguished from true snakes by their movable eyelids and by differences in the structure of the skull bones, especially those of the lower jaw. The bones of the two halves of a lizard’s lower jaw are firmly united; those of a snake are separable. The teeth of lizards are set along the inside of the jaw, not embedded in deep sockets as in crocodilians. Although some lizards such as horned lizards and thorny devils have sharp, prickly scales, they lack the large bony armor found in the shells of turtles and as scutes along the backs and tails of crocodilians.

A

Legs and Tails

Lizards move in a variety of ways, depending on body structure and habitat. Crawling on four legs is the most common mode. The collared lizard and the basilisk can run quickly on well-developed hind legs. Some lizards are good swimmers, and a number are adapted for climbing trees or rocks. The flying dragon has expanded ribs that allow it to glide through the air from tree to tree. The legs of some lizards are greatly shortened, or vestigial, making animals such as the glass lizard or slowworm snakelike in appearance.

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In many species of lizard, the long tail is fragile and easily broken off. A predator that grabs the lizard by the tail gets a small meal when the tail breaks off, but the lizard itself escapes and is able to regenerate a new tail. Other species have strong tails. The tail of some tree-living species of chameleons is adapted for grasping branches. Monitors and marine iguanas use their muscular tails for swimming.

B

Skin

Lizards shed their skin as they grow, usually in small patches. By contrast, snakes typically shed their outer layer of skin intact. Many lizards have colors or skin patterns that help them blend in with their environments and make them hard to see. The chameleon and the anole can change their skin colors as the external environment changes, providing active camouflage. Chameleons can also change skin color to express threats as well as anger and fear. In some other species of lizard, males have brightly colored areas of skin to attract females and warn rivals from their territories. Some iguanas have a raised crest of skin along their backs for decoration. Marine iguanas on the Galápagos Islands are dark colored to better absorb heat from the Sun after swimming in cold seawater.

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