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, often four-legged, cold-blooded, with an integumentary system comprising 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 water and oils.
Lizards have scales on their skin which may be tubercular or have ossified encrustations called osteoderms.
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 defense mechanism. Many lizards are good climbers or fast sprinters. Some can run bipedally, such as the collared lizard and the world's fastest lizard, the spiny-tailed iguana in the genus Ctenosaura.
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 "American chameleon," "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.
Only two lizard species have proven to be venomous: the Mexican beaded lizard and the closely-related Gila monster, both of which live in northern Mexico and the southwest United States. Even though there are myths and legends abound about these creatures, and their bite can cause serious injury, no human fatalities have ever been recorded.
Research at the University of Melbourne, Australia proposes that some lizards in the iguanas and monitor (lizard) families may have venom-producing glands. If proven to be true, however, these would pose little or no danger to humans, as the poison is introduced slowly by chewing, rather than subcutaneous injection as with venomous snakes. According to this study, nine toxins previously thought to only occur in snakes have been discovered out of several thousand. Prior to this theory, swelling and irritation from lizard bites was believed due to bacterial infection and in most cases this is likely, but the study suggests it may be due to partial envenomation. The scientists behind these findings are calling for a re-evaluation of the classification system for lizard species to form a venom clade and if successful may result in changes to the beliefs regarding the evolution of lizards, snakes, and venom.
Relationship to humans
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 stalk, 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). The Moche people of ancient Peru worshipped animals and often depicted lizards in their art.
Lizards in the Scincomorpha family, which include skinks (such as the blue-tailed skink), often have shiny, iridescent scales that appear moist. 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.
Lizards as pets
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.
- Scientific classification
- Kingdom: Animalia
- Phylum: Chordata
- Superclass: Tetrapoda
- Class: Sauropsida
- Order: Squamata
- Suborder: Lacertilia*: GŁnther, 1867
Suborder Lacertilia (Sauria) - (Lizards)
- Family Bavarisauridae
- Family Eichstaettisauridae
- Infraorder Iguania
- Family Arretosauridae
- Family Euposauridae
- Family Corytophanidae (casquehead lizards)
- Family Iguanidae (iguanas and spinytail iguanas)
- Family Phrynosomatidae (earless, spiny, tree, side-blotched and horned lizards)
- Family Polychrotidae (anoles)
- Family Leiosauridae (see Polychrotinae)
- Family Tropiduridae (neotropical ground lizards)
- Family Liolaemidae (see Tropidurinae)
- Family Leiocephalidae (see Tropidurinae)
- Family Crotaphytidae (collared and leopard lizards)
- Family Opluridae (Madagascar iguanids)
- Family Hoplocercidae (wood lizards, clubtails)
- Family Priscagamidae
- Family Isodontosauridae
- Family Agamidae (agamas)
- Family Chamaeleonidae (chameleons)
- Infraorder Gekkota
- Family Gekkonidae (geckos)
- Family Pygopodidae (legless lizards)
- Family Dibamidae (blind lizards)
- Infraorder Scincomorpha
- Family Paramacellodidae
- Family Slavoiidae
- Family Scincidae (skinks)
- Family Cordylidae (spinytail lizards)
- Family Gerrhosauridae (plated lizards)
- Family Xantusiidae (night lizards)
- Family Lacertidae (wall lizards or true lizards)
- Family Mongolochamopidae
- Family Adamisauridae
- Family Teiidae (tegus and whiptails)
- Family Gymnophthalmidae (spectacled lizards)
- Infraorder Diploglossa
- Family Anguidae (glass lizards)
- Family Anniellidae (American legless lizards)
- Family Xenosauridae (knob-scaled lizards)
- Infraorder Platynota (Varanoidea)
- Family Varanidae (monitor lizards)
- Family Lanthanotidae (earless monitor lizards)
- Family Helodermatidae (gila monsters Chinese water dragon & beaded lizards)
- Family Mosasauridae (marine lizards)