Kingdom: Animalia

Phylum: Chordata

Superclass: Tetrapoda

Class: Reptilia

Order: Squamata

Suborder: Lacertilia

Physical Description

Lizard (suborder Sauria), any of more than 5,500 species of reptiles belonging in the order Squamata. Lizards are scaly-skinned reptiles that are usually distinguished from snakes by the possession of legs, movable eyelids, and external ear openings. However, some traditional (that is, non-snake) lizards lack one or more of these features. For example, limb degeneration and loss has occurred in glass lizards (Ophisaurus) and other lizard groups. Movable eyelids have been lost in some geckos, skinks, and night lizards. External ear openings have disappeared in some species in the genera Holbrookiaand Cophosaurus. Most of the living species of lizards inhabit warm regions, but some are found near the Arctic Circle in Eurasia and others range to the southern tip of South America.

Lizards are by far the most diverse group of modern reptiles in body shape and size. They range from 2 cm (0.8 inch) snout to vent in geckos (family Gekkonidae) to 3 metres (10 feet) in total length in monitor lizards (family Varanidae). The weight of adult lizards ranges from less than 0.5 gram (0.02 ounce) to more than 150 kg (330 pounds). The popular conception of a lizard as a scampering reptile about 30 cm (12 inches) in total length with a slender tail may be applied accurately only to a small number of species. Representatives of several families are limbless and resemble snakes, whereas others have long hind legs that permit bipedal locomotion. Male lizards may be outfitted with a wide array of ornamentation—such as extensible throat fans and frills, throat spines, horns or casques on the head, and tail crests.

Lizards occupy diverse habitats that range from underground warrens and burrows to the surface and elevated vegetation. Some move slowly and rely on cryptic coloration for protection, whereas others can run swiftly across desert sands. Lizards of the family Mosasauridae, an extinct group, were strictly marine. Some mosasaurs were giants and grew to lengths of 10 metres (33 feet). One living lizard, the marine iguana (Amblyrhynchus cristatus) of the Galapagos Islands, feeds on algae in the sea. However, it spends much of its time basking on lavarocks on the islands. No other extant lizard species is marine, but several are partially aquatic and feed on freshwater organisms.

Most lizards reproduce by laying eggs. In some small species, the number of eggs is rather uniform for each laying or clutch. For example, all anoles (Anolis) lay but a single egg at a time, many geckos lay one or two eggs (depending upon the species), and some skinks have clutches of two eggs. A more general rule is that clutch size varies with the size, age, and condition of the mother. A clutch of four to eight eggs may be considered typical, but large lizards such as the iguanas may lay 50 or more eggs at one time. Lizard eggs are usually leathery-shelled and porous; they can expand by the absorption of moisture as the embryos grow. An exception occurs in the majority of egg-laying geckos, whose eggs have shells that harden soon after they are deposited and then show no further change in size or shape.