reptile

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reptile,

name for the dry-skinned, usually scaly, cold-blooded vertebrates (see ChordataChordata
, phylum of animals having a notochord, or dorsal stiffening rod, as the chief internal skeletal support at some stage of their development. Most chordates are vertebrates (animals with backbones), but the phylum also includes some small marine invertebrate animals.
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) of the order Reptilia. Reptiles are found in a variety of habitats throughout the warm and temperate regions (except on some islands), with the greatest variety in the tropics. Reptiles differ from other terrestrial vertebrates (birds and mammals) in that they are cold-blooded, that is, they lack an effective system for regulating their body temperature, which tends to approach that of the environment. For this reason reptiles are not found in the coldest regions of the world, and they hibernate in cool winter areas.

They range in size from 2-in.-long (5-cm) lizards to 30-ft-long (9-m) snakes. They typically have low-slung bodies with long tails, supported by four short legs that project outward from the sides of the body; however, all snakes are limbless. Although reptiles are fundamentally a terrestrial group, some are adapted to living in water. All breathe air by means of lungs and have thick, waterproof skins designed for retaining body moisture. Unlike amphibiansamphibian,
in zoology, cold-blooded vertebrate animal of the class Amphibia. There are three living orders of amphibians: the frogs and toads (order Anura, or Salientia), the salamanders and newts (order Urodela, or Caudata), and the caecilians, or limbless amphibians (order
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, they do not possess gills or breathe water at any stage of their development, and nearly all lay their eggs or bear their young on land.

The reptilian egg has a porous shell and a system of membranes designed to protect the embryo from desiccation. It also has a large quantity of yolk for nourishment. This type of egg is typical of terrestrial vertebrates, and is very different from the simple, unprotected eggs of fishes and amphibians, which are laid in the water. Fertilization is internal in reptiles, and males have copulatory organs. Females of most species lay eggs, but in some the egg is incubated and hatched internally. In a very few there is true live birth, with the young nourished by a primitive placenta instead of an egg yolk.

Types of Reptiles

Living reptiles are classified in four orders. The turtlesturtle,
a reptile of the order Chelonia, with strong, beaked, toothless jaws and, usually, an armorlike shell. The shell normally consists of bony plates overlaid with horny shields.
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, order Chelonia, have a protective bony shell, usually covered with horny plates. They are mostly aquatic in habits although some (see tortoisetortoise
, common name for a terrestrial turtle, especially one of the family Testudinidae. Tortoises inhabit warm regions of all continents except Australia. They have club-shaped feet with reduced toes adapted for walking on land, and nearly all have high-domed shells.
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) are adapted to land. They are the oldest living reptiles, having existed nearly unchanged since the Triassic period. Members of the order Crocodilia, which includes alligatorsalligator,
large aquatic reptile of the genus Alligator, in the same order as the crocodile. There are two species—a large type found in the S United States and a small type found in E China. Alligators differ from crocodiles in several ways.
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, caimans, crocodilescrocodile,
large, carnivorous reptile of the order Crocodilia, found in tropical and subtropical regions. Crocodiles live in swamps or on river banks and catch their prey in the water. They have flattened bodies and tails, short legs, and powerful jaws.
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, and gavialsgavial
, large reptile of the crocodile order, found in rivers from Pakistan to Myanmar. Also called gharial, the gavial (Gavialis gangeticus) is distinguished from the crocodiles and alligators by its extremely long, slender, parallel-sided snout.
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, are large, carnivorous reptiles of tropical and subtropical swamps and rivers. They constitute the only remaining order of the great reptilian subclass Archosauria, or ruling reptiles, which includes the extinct dinosaursdinosaur
[Gr., = terrible lizard], extinct land reptile of the Mesozoic era. The dinosaurs, which were egg-laying animals, ranged in length from 2 1-2 ft (91 cm) to about 127 ft (39 m).
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. The order Squamata includes the lizardslizard,
a reptile of the order Squamata, which also includes the snake. Lizards form the suborder Sauria, and there are over 3,000 lizard species distributed throughout the world (except for the polar regions), with the greatest number found in warm climates.
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 (suborder Sauria) and snakessnake,
common name for an elongated, limbless reptile of the order Squamata, which also includes the xlizards. Most snakes live on the ground, but some are burrowers, arboreal, or aquatic; one group is exclusively marine. In temperate climates they hibernate.
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 (suborder Serpentes). Nearly all members of this large and successful modern order are terrestrial. The order Rhynchocephalia has a single living member, the tuataratuatara
or tuatera
, lizardlike reptile, Sphenodon punctatus, last survivor of the reptilian order Rhynchocephalia, which flourished in the early Mesozoic era before the rise of the dinosaurs.
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, a lizardlike reptile of New Zealand.

Evolution

Reptiles first evolved from amphibians about 250 million years ago in the Carboniferous period and were dominant in the world's fauna during the Mesozoic era, sometimes called the Age of Reptiles. The dinosaurs, the marine Ichthyosaurus and PlesiosaurusPlesiosaurus
, genus of extinct predatory marine reptiles that arose in the Triassic period of geologic time and continued into the Jurassic and Cretaceous periods. Plesiosaurs became extinct at the close of the Mesozoic era.
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, and the flying pterosaurs reached the peak of their development and distribution in the later part of this era (late Cretaceous period). Mammallike reptiles appeared very early in reptilian history and by the Triassic period had given rise to mammals. Bird ancestors arose from precursors of the dinosaurs; the first known birds lived in the Jurassic. The only reptiles that survived into the Cenozoic era belonged to the presently living orders. The approximately 6,000 living reptile species represent a very small fraction of this once vast class.

Bibliography

See R. Conant, Field Guide to Reptiles and Amphibians (1958); A. Bellairs, The Life of Reptiles (2 vol., 1970); K. P. Schmidt and R. F. Inger, Living Reptiles of the World (1957, repr. 1972); H. M. Smith and E. Brodie, Reptiles of North America (1982); H. M. Smith and H. S. Zim, Reptiles and Amphibians (1987).

What does it mean when you dream about a reptile?

See Dinosaur, Lizard, Serpent, Snake, or Turtle.

reptile

[′rep‚tīl]
(vertebrate zoology)
Any member of the class Reptilia.

reptile

any of the cold-blooded vertebrates constituting the class Reptilia, characterized by lungs, an outer covering of horny scales or plates, and young produced in amniotic eggs. The class today includes the tortoises, turtles, snakes, lizards, and crocodiles; in Mesozoic times it was the dominant group, containing the dinosaurs and related forms