August 10, 2011


Reptiles are animals in the (Linnaean) class Reptilia. They are characterized by breathing air, laying shelled eggs (except for some vipers and constrictor snakes that give live birth), and having skin covered in scales and/or scutes. Reptiles are classically viewed as having a "cold-blooded" metabolism. They are tetrapods (either having four limbs or being descended from four-limbed ancestors). Modern reptiles inhabit every continent with the exception of Antarctica, and four living orders are currently recognized:

* Crocodilia (crocodiles, gavials, caimans, and alligators): 23 species
* Sphenodontia (tuataras from New Zealand): 2 species
* Squamata (lizards, snakes, and worm lizards): approximately 7,900 species
* Testudines (turtles and tortoises): approximately 300 species

Unlike amphibians, reptiles do not have an aquatic larval stage. As a rule, reptiles 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 placenta analogous to those of mammals, with some providing initial care for their hatchlings. Extant reptiles range in size from a tiny gecko, Sphaerodactylus ariasae, which can grow up to 1.7 cm (0.6 in) to the saltwater crocodile, Crocodylus porosus, which may reach 6 m in length and weigh over 1,000 kg.

The reptiles were from the outset of classification grouped with the amphibians. Linnaeus, working from species-poor Sweden, where the common adder and grass snake are often found hunting in water, included all reptiles and amphibians in class "III – Amphibia" in his Systema Naturæ.[1] The terms "reptile" and "amphibian" were largely interchangeable, "reptile" (from Latin repere, "to creep") being preferred by the French.[2] Josephus Nicolaus Laurenti was the first to formally use the term "Reptilia" for an expanded selection of reptiles and amphibians basically similar to that of Linnaeus.[3] Today, it is still common to treat the two groups under the same heading as herptiles.

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