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'''Reptiles''' are [[animals]] in the ([http://en.wikipedia.org/wiki/Linnaean_taxonomy Linnaean]) class Reptilia characterized by [[breathing]] [[air]], a "cold-blooded" (poikilothermic) [[metabolism]], laying tough-shelled [http://en.wikipedia.org/wiki/Amniote amniotic eggs] (or retaining the same membrane system in [[species]] with live [[birth]]), and skin with scales or scutes. They are [http://en.wikipedia.org/wiki/Tetrapod tetrapods] (either having four limbs or being descended from four-limbed [[ancestors]]) and lay [http://en.wikipedia.org/wiki/Amniote amniotic eggs], in which the embryo is surrounded by a membrane called the [http://en.wikipedia.org/wiki/Amnion amnion]. Modern reptiles inhabit every continent  with the exception of Antarctica, and four living [[orders]] are currently [[recognized]]:

'''Reptiles''' are [[animals]] in the ([https://en.wikipedia.org/wiki/Linnaean_taxonomy Linnaean]) class Reptilia characterized by [[breathing]] [[air]], a "cold-blooded" (poikilothermic) [[metabolism]], laying tough-shelled [https://en.wikipedia.org/wiki/Amniote amniotic eggs] (or retaining the same membrane system in [[species]] with live [[birth]]), and skin with scales or scutes. They are [https://en.wikipedia.org/wiki/Tetrapod tetrapods] (either having four limbs or being descended from four-limbed [[ancestors]]) and lay [https://en.wikipedia.org/wiki/Amniote amniotic eggs], in which the embryo is surrounded by a membrane called the [https://en.wikipedia.org/wiki/Amnion amnion]. Modern reptiles inhabit every continent  with the exception of Antarctica, and four living [[orders]] are currently [[recognized]]:

* ''[http://en.wikipedia.org/wiki/Crocodilia Crocodilia]'' (crocodiles, gavials, caimans, and alligators): 23 species

* ''[https://en.wikipedia.org/wiki/Crocodilia Crocodilia]'' (crocodiles, gavials, caimans, and alligators): 23 species

* ''[http://en.wikipedia.org/wiki/Sphenodontia Sphenodontia]'' (tuataras from New Zealand): 2 species

* ''[https://en.wikipedia.org/wiki/Sphenodontia Sphenodontia]'' (tuataras from New Zealand): 2 species

* ''[http://en.wikipedia.org/wiki/Squamata Squamata]'' (lizards, snakes, and worm lizards): approximately 7,900 species

* ''[https://en.wikipedia.org/wiki/Squamata Squamata]'' (lizards, snakes, and worm lizards): approximately 7,900 species

* ''[http://en.wikipedia.org/wiki/Testudines Testudines]'' (turtles and tortoises): approximately 300 species

* ''[https://en.wikipedia.org/wiki/Testudines Testudines]'' (turtles and tortoises): approximately 300 species

The [[majority]] of reptile species are ''oviparous'' (egg-laying), although certain [[species]] of squamates are capable of giving live birth. This is achieved by either ovoviviparity (egg retention) or viviparity ([[birth]] of offspring without the development of calcified eggs). Many of the viviparous species feed their fetuses through various forms of [http://en.wikipedia.org/wiki/Placenta placenta] [[analogous]] to those of [[mammals]], with some providing initial care for their hatchlings. Extant reptiles range in size from a tiny gecko, [http://en.wikipedia.org/wiki/Jaragua_Sphaero Sphaerodactylus ariasae], that [[grows]] to only 1.6 cm (0.6 in) to the [http://en.wikipedia.org/wiki/Saltwater_Crocodile saltwater crocodile], Crocodylus porosus, that may reach 6 m in length and weigh over 1,000 kg. The [[science]] dealing with ''reptiles'' is called [http://en.wikipedia.org/wiki/Herpetology herpetology].[http://en.wikipedia.org/wiki/Reptiles]

The [[majority]] of reptile species are ''oviparous'' (egg-laying), although certain [[species]] of squamates are capable of giving live birth. This is achieved by either ovoviviparity (egg retention) or viviparity ([[birth]] of offspring without the development of calcified eggs). Many of the viviparous species feed their fetuses through various forms of [https://en.wikipedia.org/wiki/Placenta placenta] [[analogous]] to those of [[mammals]], with some providing initial care for their hatchlings. Extant reptiles range in size from a tiny gecko, [https://en.wikipedia.org/wiki/Jaragua_Sphaero Sphaerodactylus ariasae], that [[grows]] to only 1.6 cm (0.6 in) to the [https://en.wikipedia.org/wiki/Saltwater_Crocodile saltwater crocodile], Crocodylus porosus, that may reach 6 m in length and weigh over 1,000 kg. The [[science]] dealing with ''reptiles'' is called [https://en.wikipedia.org/wiki/Herpetology herpetology].[https://en.wikipedia.org/wiki/Reptiles]

==Origin==

==Origin==

The [[origin]] of the reptiles lies about 320–310 million years ago, in the steaming swamps of the late [http://en.wikipedia.org/wiki/Carboniferous Carboniferous  period], when the first reptiles evolved from advanced [http://en.wikipedia.org/wiki/Reptiliomorpha reptiliomorph] labyrinthodonts. The oldest trace of reptiles is a series of footprints from the [[fossil]] strata of Nova Scotia, dated to 315 million years ago. The tracks are attributed to Hylonomus, the oldest known reptile in the [[biological]] sense of the [[word]]. It was a small, lizard-like animal, about 20 to 30 cm (8–12 in) long, with numerous sharp teeth indicating an insectivorous diet. Other examples include Westlothiana  (for the moment considered to be more closely related to [http://en.wikipedia.org/wiki/Amphibians amphibians] than to amniotes) and Paleothyris, both of similar build and presumably similar [[habit]]. One of the best known early reptiles is [http://en.wikipedia.org/wiki/Mesosaurus Mesosaurus], a genus from the early Permian that had returned to water, feeding on fish. The earliest reptiles were largely overshadowed by bigger labyrinthodont amphibians such as Cochleosaurus, and remained a small, inconspicuous part of the fauna until after the small ice age at the end of the Carboniferous.[http://en.wikipedia.org/wiki/Reptiles#Rise_of_the_reptiles]

The [[origin]] of the reptiles lies about 320–310 million years ago, in the steaming swamps of the late [https://en.wikipedia.org/wiki/Carboniferous Carboniferous  period], when the first reptiles evolved from advanced [https://en.wikipedia.org/wiki/Reptiliomorpha reptiliomorph] labyrinthodonts. The oldest trace of reptiles is a series of footprints from the [[fossil]] strata of Nova Scotia, dated to 315 million years ago. The tracks are attributed to Hylonomus, the oldest known reptile in the [[biological]] sense of the [[word]]. It was a small, lizard-like animal, about 20 to 30 cm (8–12 in) long, with numerous sharp teeth indicating an insectivorous diet. Other examples include Westlothiana  (for the moment considered to be more closely related to [https://en.wikipedia.org/wiki/Amphibians amphibians] than to amniotes) and Paleothyris, both of similar build and presumably similar [[habit]]. One of the best known early reptiles is [https://en.wikipedia.org/wiki/Mesosaurus Mesosaurus], a genus from the early Permian that had returned to water, feeding on fish. The earliest reptiles were largely overshadowed by bigger labyrinthodont amphibians such as Cochleosaurus, and remained a small, inconspicuous part of the fauna until after the small ice age at the end of the Carboniferous.[https://en.wikipedia.org/wiki/Reptiles#Rise_of_the_reptiles]

[[Category: Biology]]

[[Category: Biology]]

[[Category: Zoology]]

[[Category: Zoology]]