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Any of various usually cold-blooded egg-laying vertebrates often grouped in the class Reptilia, having dry skin covered with scales or horny plates and breathing by means of lungs, and including the snakes, lizards, crocodilians, and turtles. In some classification systems, birds are considered to be reptiles because they are descended from reptilian dinosaurs.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.
reptileany member of the vertebrate class Reptilia, including turtles and tortoises (Chelonia), lizards and snakes (Squamata), crocodiles (Crocodilia), the extinct dinosaurs (Ornithischia, Saurischia), pterodactyls (Pterosauria), plesiosaurs (Plesiosauria), and the ancestors of mammals, the Therapsida. All reptiles are egg-laying and present-day forms are POIKILOTHERMS, though some dinosaurs may have been HOMOIOTHERMS.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005