Lizards typically have four legs with five toes on each foot, although a few, such as the worm lizard and the so-called glass snake, are limbless, retaining only internal vestiges of legs. Lizards are also distinguished from snakes by having ear openings, movable eyelids, and less flexible jaws. As in snakes, there is a chemosensory organ opening in the roof of the mouth. The tongue, which may be short and wide, slender and forked, or highly extendible, conveys particles from the environment to this organ. The skin of the lizard is scaly and in most species is molted in irregular patches. Members of several lizard families, notably the chameleons, undergo color changes under the influence of environmental and emotional stimuli.

Many lizards are arboreal, and many terrestrial species are well adapted for climbing. They are often fast runners, some achieving speeds of over 15 mi (24 km) per hr. Some are adapted for burrowing. Most can swim and a few lead a semiaquatic existence, among them the single marine species, an iguana of the Galapagos Islands. Gliding forms, the flying dragons, are found in the forests of SE Asia. The gila monster and the related beaded lizard of the North American deserts are the only known poisonous lizards; some other lizards, such as the lace monitor of Australia, produce a nonfatal venom. Despite folklore, the bite of the gecko is not poisonous. Members of most species are carnivorous, feeding especially on insects, but some are herbivorous or omnivorous.

Fertilization is internal in lizards; males have paired copulatory organs, characteristic of the order. In most species females lay eggs, which they bury in the ground, but in some the eggs are incubated in the oviducts and hatched as they are laid. In both types the young have a special temporary tooth for rupturing the shell. In a few species there is true viviparity, or live birth, with the young nourished by a simple placenta.

The greatest number of species in the United States is found in the South and West. The majority are members of the iguana family, including the collared lizards, swifts, utas, horned lizards (popularly known as horned toads), and the so-called American chameleon, or anole. These are day-active lizards commonly seen basking on rocks. Most are valuable destroyers of insects.

Lizards are classified in the phylum Chordata, subphylum Vertebrata, class Reptilia, order Squamata, suborder Sauria.

Any of about 4,450 species of reptiles constituting the suborder Sauria. They are most diverse and abundant in the tropics but are found from the Arctic Circle (one species) to southern Africa, South America, and Australia. Like snakes, lizards have scales, paired male copulatory organs, and a flexible skull. Typical lizards have a moderately cylindrical body, four well-developed legs (although some lizards are legless), a tail slightly longer than the head and body combined, and movable lower eyelids. They range in size from 1-in. (3-cm) geckos to the 10-ft (3-m) Komodo dragon, but most are about 12 in. (30 cm) long. Ornamentation includes crests on the head, back, or tail; spines; brightly coloured throat fans; and throat frills. Most species feed on insects and rodents, but some, such as the iguana, eat plants. Seealso Gila monster; horned toad.

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Any of about 14 species of lizards of the genus Phrynosoma, family Iguanidae. They usually have daggerlike head spines (horns) and a flattened oval body with pointed fringe scales along the sides. Species range from about 3 to 5 in. (8 to 13 cm) long. They are found from British Columbia, Can., south to Guatemala and from the U.S. states of Arkansas and Kansas westward, usually in desert or semidesert sandy country. They eat mainly ants. They hide by changing their colour pattern and wriggling sideways into the sand until all but the head is covered. They may defend themselves by inflating the body quickly and (rarely) spurting blood from the eyes.

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