Lizard
2008/9 Schools Wikipedia Selection. Related subjects: Insects, Reptiles and Fish
| Lizard Fossil range: Jurassic - Recent |
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 "Lacertilia", from Ernst Haeckel's Artforms of Nature, 1904
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Lizards are reptiles of the order Squamata, normally possessing four legs and external ear openings. The adult length of species within the order range from a few centimetres (some Caribbean geckos) to nearly three metres ( Komodo Dragons).
Description
Lizards are reptiles, often four-legged, with an integumentary system comprising scales, with a skull composed of quadrate bones. Lizards possess external ears and most have movable eyelids. Encompassing forty families, there is tremendous variety in colour, appearance and size. Due to their smooth, shiny appearance, some lizards can appear slimy or slippery although 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 defence 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 of the genus Ctenosaura.
Many lizards can change colour in response to their environments or in times of stress. The most familiar example is the chameleon, but more subtle colour changes occur in other lizard species as well such as the anole, also known as the "American chameleon," "house chameleon" or "chamele".
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.
Diet
Lizards feed on a wide variety of foods including fruits and vegetation, insects, small tetra pods, carrion and even (in the cases of large predator lizards) large prey such as deer and other big animals as well.
Venomous Lizards
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 myths and legends abound about these creatures, and their bite can cause serious injury, no human fatalities have ever been recorded.
Researchers at the University of Melbourne, Australia propose that some lizards in the agamid and monitor families may have venom-producing glands. According to this study, nine toxins out of several thousand previously thought to only occur in snakes have been discovered between several monitor species and a bearded dragon. Prior to this theory, swelling and irritation from lizard bites was believed due to bacterial infection, but this hypothesis suggests that 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. Only the very largest lizard species pose threat of death; the Komodo dragon, for example, has been known to stalk, attack, and kill humans. The venom of the Gila monster and beaded lizard is not usually 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, Green 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.
Classification
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Image:Lizards at Iguazu.jpg
Two Tegus, Tupinambis merianae
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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)