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Any of the approximately 8,700 species of the class Reptilia, the group of air-breathing vertebrates that have internal fertilization and a scaly body and are cold-blooded. Most species have short legs (or none) and long tails, and most lay eggs. Living reptiles include the scaly reptiles (snakes and lizards; order Squamata), the crocodiles (Crocodylia), the turtles (Testudines), and the unique tuatara (Sphenodontida). Being cold-blooded, reptiles are not found in very cold regions; in regions with cold winters, they usually hibernate. They range in size from geckos that measure about 1 in. (3 cm) long to the python, which grows to 30 ft (9 m); the largest turtle, the marine leatherback, weighs about 1,500 lb (680 kg). Extinct reptiles include the dinosaurs, the pterosaurs, and the dolphinlike ichthyosaurs.
This entry comes from Encyclopædia Britannica Concise. For the full entry on reptile, visit Britannica.com.