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reptileThey 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 amphibians, 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 ReptilesLiving reptiles are classified in four orders. The turtles, order Chelonia, have a protective bony shell, usually covered with horny plates. They are mostly aquatic in habits although some (see tortoise) 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 alligators, caimans, crocodiles, and gavials, 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 dinosaurs. The order Squamata includes the lizards (suborder Sauria) and snakes (suborder Serpentes). Nearly all members of this large and successful modern order are terrestrial. The order Rhynchocephalia has a single living member, the tuatara, a lizardlike reptile of New Zealand.
EvolutionReptiles 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 plesiosaurus, 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.
BibliographySee 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).
The Columbia Encyclopedia. Copyright © 2001-09 Columbia University Press. All rights reserved.
Crocodilia : 23 species
Sphenodontia : 2 species
Squamata : approximately 7,900 species
Testudines : approximately 300 species The majority of reptile species are oviparous, although certain species of squamates are capable...more »
- Plesiosaurus
Plesiosaurus, 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 a...
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Kite, in zoology, common name for a bird of the family Accipitridae, which also includes the hawk. Kites are found near water and marshes in warm parts of the world. They prey chiefly on repti...
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Pentastomida, tongue worms, small phylum of fewer than 100 species of parasites living in the upper respiratory passages of reptiles, and occasionally of birds and mammals. They are closely re...
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Dragon, mythical beast usually represented as a huge, winged, fire-breathing reptile. For centuries the dragon has been prominent in the folklore of many peoples; thus, its physical characteri...
- gavial
Gavial, 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 alligator...
- nest
Nest, structure for the reception and incubation of the eggs of birds, reptiles, insects, and some fish or for the parturition of mammals, and also for the care of the young during their perio...
- tuatara
Tuatara 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. ...
- crocodile
Crocodile, 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 ha...
- salamander
Salamander, an amphibian of the order Urodela, or Caudata. Salamanders have tails and small, weak limbs; superficially they resemble the unrelated lizards (which are reptiles), but they are ea...
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snake, in zoology
Snake, common name for an elongated, limbless reptile of the order Squamata, which also includes the lizards. Most snakes live on the ground, but some are burrowers, arboreal, or aquatic; one ...
