Lizard

Lizards are reptiles of the order Squamata, normally possessing four legs, external ear openings and movable eyelids. The adult length of species within the order range from a few centimeters (some Caribbean geckos) to nearly three meters (Komodo Dragons).

Lizards are reptilian, four-legged, cold-blooded, with an integumentary system comprised of scales, with a skull composed of quadrate bones. Lizards also possess external ears and movable eyelids. Encompassing forty families, there is tremendous variety in color, appearance and size. Due to their smooth, shiny appearance, lizards can appear slimy or slippery; their skin is actually very dry due to a lack of pores to excrete lubricants.

Most lizards are oviparous, though a few species are viviparous. Many are also capable of regeneration of lost limbs or tails.

Some lizard species, including the glass lizard and legless lizards, have some vestigial structures though no functional legs. They are distinguished from true snakes by the presence of eyelids and ears and a tail that can sometimes break off as a physical defence mechanism.

Many lizards can change color in response to their environments or in times of stress. The most familiar example is the chameleon, but more subtle color changes occur in other lizard species as well (most notably the anole, also known as the "house chameleon" or "chamele").

Lizards feed on a wide variety of foods including fruits and vegetation, insects, small tetrapods, carrion and even (in the cases of large predator lizards) large prey such as deer. Until very recently, it was thought that only two lizard species were venomous: the Mexican beaded lizard and the closely-related Gila monster, both of which live in northern Mexico and the southwest United States. However research at the University of Melbourne, Australia and Pennsylvania State University has revealed that in fact many lizards in the iguanians and monitor (lizard) families have venom-producing glands. Typically these pose little danger to humans, as their poison is introduced slowly by chewing, rather than subcutaneous injection as with venomous snakes. Nine toxins previously thought to only occur in snakes have been discovered, as well as a number of previously unseen chemicals. Before this discovery, swelling and bleeding from lizard bites was believed due to bacterial infection but is now known to be due to venom injection. These findings have caused a re-evaluation of the classification system for lizard species to form a venom clade and may result in radical changes to the beliefs regarding the evolution of lizard, snake and venom.

Most lizard species are harmless to humans (most species native to North America, for example, are incapable even of drawing blood with their bites). Only the very largest lizard species pose threat of death; the Komodo dragon, for example, has been known to attack and kill humans and their livestock. The venom of the gila monster and beaded lizard is not deadly but they can inflict extremely painful bites due to powerful jaws. The chief impact of lizards on humans is positive as they are significant predators of pest species; numerous species are prominent in the pet trade; some are eaten as food (for example, iguanas in Central America); and lizard symbology plays important, though rarely predominant roles in some cultures (e.g. Tarrotarro in Australian mythology).

Lizards in the Scincomorpha family, which include skinks (such as the blue-tailed skink), often have shiny, iridescent scales that appear moist. Like all other lizards, they are dry-skinned and generally prefer to avoid water. All lizards are capable of swimming if needed and a few (such as the Nile monitor) are quite comfortable in aquatic environments.

Species of lizards sold as pets include iguanas, bearded dragon, leopard geckos, tegus, and monitor lizards. In general, lizards require more maintenance than other exotic pets. Finding a veterinarian whose practice includes lizards is also important.