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.
See W. M. Milstead, ed., Lizard Ecology (1967) H. S. Fitch, Reproductive Cycles of Lizards and Snakes (1970) B. R. Headstrom, Lizards as Pets (1971).
See more Encyclopedia articles on: Vertebrate Zoology
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