Difference between revisions of "Lizard" - New World Encyclopedia

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'''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 (biology)|order]] range from a few [[centimeter]]s (some [[Caribbean Sea|Caribbean]] [[gecko]]s) to nearly three meters ([[Komodo Dragon]]s).
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'''Lizard''' is any of the numerous [[reptile]]s of the suborder Sauria (or Lacertilia) of the order Squamata. Lizards generally are distinguished from [[snake]]s—which also belong to order Squamata, but are placed in suborder Serpentes—by the presence of legs, although some lizards are legless. Lizards also are differentiated from snakes by having external ear openings and movable eyelids.  
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Some well-known types of lizards are [[iguana]]s, [[skink]]s, [[gecko]]s, [[chameleon]]s, [[gila monster]]s, and [[horned toad]]s.
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Lizards are found in all continents except [[Antarctica]], with one species even found in the Arctic Circle. However, snakes are most abundant in tropical areas.  
  
 
==Description==
 
==Description==
Lizards are reptilian, four-legged, [[cold-blooded]], with an [[integumentary system]] comprised of [[scale]]s, with a skull composed of [[quadrate bone]]s. Lizards also possess external ears and movable eyelids.  Encompassing forty [[Family (biology)|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 [[Sweating|pore]]s to excrete lubricants.
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The order Squamata is composed of lizards (suborder Squamata) and snakes (suborder Serpentes). Members of this reptilian order are distinguished by having a lower jaw that is not joined directly to the skull, scales, and the presence of paired reproductive organs in the male (Towle 1989).
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Lizards have less flexible jaws than snakes, movable eyelids, external ear openings, and most have four-well developed limbs, often with five toes on each foot. Lizards have an [[integumentary system]] comprised of [[scale]]s, with a skull composed of [[quadrate bone]]s. Some lizard species, including the [[glass lizard]] and [[Pygopodidae|legless lizards]], lack functional legs although there are some [[vestigial]] structures. These 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. Lizards typically have a tail longer than the body and, like snakes, a chemosensory organ in the mouth.
  
Most lizards are [[oviparous]], though a few species are [[viviparous]].  Many are also capable of [[regeneration (biology)|regeneration]] of lost limbs or tails.
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Encompassing forty [[Family (biology)|families]] and about 3,000 [[species]], lizards offer a tremendous variety in color, appearance, and sizeDue to their smooth, shiny appearance, lizards can appear slimy or slippery; their skin is actually very dry due to a lack of [[Sweating|pore]]s to excrete lubricants.
  
Some lizard species, including the [[glass lizard]] and [[Pygopodidae|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.
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Most lizards are carnivorous, but preying on insects or small animals, such as [[rodent]]s. However, some eat plants or are omnivorous.
  
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 [[Polychrotidae|anole]], also known as the "house chameleon" or "chamele").
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Most lizards are [[oviparous]] (lay [[egg (biology)|eggs]], most buried in ground but some hatched as laid), though a few species are [[viviparous]] (live birth). Fertilization is internal. Many are also capable of [[regeneration (biology)|regeneration]] of lost limbs or tails.
  
==Diet==
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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 [[Polychrotidae|anole]], also known as the "house chameleon" or "chamele"). ''Anolis carolinensis'', a common lizared of [[North America]], can change color and is often called a chameleon, but true chameleons are limited to [[Africa]] and [[Madagascar]].
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The adult length of species within the order range from a few centimeters (some Caribbean geckos) to nearly three meters ([[komodo dragon]]s). Iguans can reach one meter in length (Towle 1989). The Komodo dragon can reach 140 kilograms. Monitors (such as the Komodo dragon) are similar to snakes in that they have deeply forked tongues that serve as sense organs, and consume large prey whole (Towle 1989).
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==Diet and venom==
 
[[Image:Emperorflatlizard.jpg|thumb|left|150px|An emperor flat lizard]]
 
[[Image:Emperorflatlizard.jpg|thumb|left|150px|An emperor flat lizard]]
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 [[venom (poison)|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 [[iguania]]ns and [[monitor (lizard)]] families have [[Venom (poison)|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.<ref>{{ cite journal | url = http://www.newscientist.com/article.ns?id=dn8331 | last = Young | first = Emma | year = 2005 | journal = New Scientist | accessdate = 2007-06-02 | title = Lizards' poisonous secret is revealed }}</ref>
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As a group, lizards feed on a wide variety of foods, including [[fruit]]s 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 [[venom (poison)|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 [[iguania]]ns and [[monitor (lizard)]] families have [[Venom (poison)|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 [[snake]]s 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 [[bacteria]]l 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 (Young 2005).
  
 
==Relationship to humans==
 
==Relationship to humans==
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== References ==
 
== References ==
{{reflist}}
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<ref>{{ cite journal | url = http://www.newscientist.com/article.ns?id=dn8331 | last = Young | first = Emma | year = 2005 | journal = New Scientist | accessdate = 2007-06-02 | title = Lizards' poisonous secret is revealed }}</ref>
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Towle
  
 
== External links ==
 
== External links ==
{{commonscat|Sauria}}
 
  
 
* [http://news.bbc.co.uk/hi/english/sci/tech/newsid_1689000/1689313.stm Tiny gecko] - the 'world's smallest' lizard
 
* [http://news.bbc.co.uk/hi/english/sci/tech/newsid_1689000/1689313.stm Tiny gecko] - the 'world's smallest' lizard

Revision as of 00:51, 11 August 2007

Lizard
Fossil range: Jurassic - Recent
"Lacertilia", from Ernst Haeckel's Artforms of Nature, 1904
"Lacertilia", from Ernst Haeckel's Artforms of Nature, 1904
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Superclass: Tetrapoda
Class: Sauropsida
Order: Squamata
Suborder: Lacertilia*
Günther, 1867
Families

Many, see text.

Lizard is any of the numerous reptiles of the suborder Sauria (or Lacertilia) of the order Squamata. Lizards generally are distinguished from snakes—which also belong to order Squamata, but are placed in suborder Serpentes—by the presence of legs, although some lizards are legless. Lizards also are differentiated from snakes by having external ear openings and movable eyelids.

Some well-known types of lizards are iguanas, skinks, geckos, chameleons, gila monsters, and horned toads.

Lizards are found in all continents except Antarctica, with one species even found in the Arctic Circle. However, snakes are most abundant in tropical areas.

Description

The order Squamata is composed of lizards (suborder Squamata) and snakes (suborder Serpentes). Members of this reptilian order are distinguished by having a lower jaw that is not joined directly to the skull, scales, and the presence of paired reproductive organs in the male (Towle 1989).

Lizards have less flexible jaws than snakes, movable eyelids, external ear openings, and most have four-well developed limbs, often with five toes on each foot. Lizards have an integumentary system comprised of scales, with a skull composed of quadrate bones. Some lizard species, including the glass lizard and legless lizards, lack functional legs although there are some vestigial structures. These 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. Lizards typically have a tail longer than the body and, like snakes, a chemosensory organ in the mouth.

Encompassing forty families and about 3,000 species, lizards offer a 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 carnivorous, but preying on insects or small animals, such as rodents. However, some eat plants or are omnivorous.

Most lizards are oviparous (lay eggs, most buried in ground but some hatched as laid), though a few species are viviparous (live birth). Fertilization is internal. Many are also capable of regeneration of lost limbs or tails.

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"). Anolis carolinensis, a common lizared of North America, can change color and is often called a chameleon, but true chameleons are limited to Africa and Madagascar.

The adult length of species within the order range from a few centimeters (some Caribbean geckos) to nearly three meters (komodo dragons). Iguans can reach one meter in length (Towle 1989). The Komodo dragon can reach 140 kilograms. Monitors (such as the Komodo dragon) are similar to snakes in that they have deeply forked tongues that serve as sense organs, and consume large prey whole (Towle 1989).

Diet and venom

An emperor flat lizard

As a group, 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 (Young 2005).

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 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).

Bearded Dragon kept as a pet.

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.

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.

Classification

Coachella Valley Fringe-toed Lizard, Uma inornata
Plumed Basilisk, Basiliscus plumifrons
Zebra-tailed Lizard, Callisaurus draconoides
Gila monster, Heloderma s. suspectum
Green tree monitor lizard, Varanus prasinus

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)
    • †Family Mosasauridae (marine lizards)

References
ISBN links support NWE through referral fees

[1]

Towle

External links

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  1. Young, Emma (2005). Lizards' poisonous secret is revealed. New Scientist.