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  • Reptiles, the class Reptilia, are an evolutionary grade of animals, comprising today's turtles, crocodilians, snakes, lizards and tuatara, as well as many extinct groups. A reptile is any amniote that is neither a mammal nor a bird. Unlike mammals, birds, and certain extinct reptiles, living reptiles have scales or scutes and are cold-blooded. Advocates of phylogenetic nomenclature regard the traditional category 'Reptilia' to be invalid, and prefer to use the 'Amniota' or rather 'Sauropsida' category, because not all descendants of a common ancestor are included. However, in practice, these non-cladistic classifications, such as reptile, fish, and amphibian, remain in use by some biologists, especially in popular books written for a general audience. The historically combined study of reptiles and amphibians is called herpetology. The earliest known reptiles originated around 315 million years ago during the Carboniferous period, having evolved from advanced reptile-like amphibians that became increasingly adapted to life on dry land.

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