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Reptiles are wonderfully diverse in size, shape, color, and lifestyle. Reptiles have a long history; they have lived on Earth for over 300 million years. Reptiles are mysterious and often misunderstood; they are feared and revered.
The reptiles, or Class Reptilia, include turtles, crocodilians, tuataras, lizards and snakes. Birds, dinosaurs, and numerous extinct groups may also be classified as reptiles.
Reptiles are vertebrates -- they have an internal skeleton with a backbone.
Reptiles are tetrapods -- they have four legs or their ancestors had four legs. (Even snakes, whose legs have been lost, are tetrapods.)
Reptiles are amniotes -- they have eggs with a waterproof shell that contains amniotic fluid.
Reptiles evolved as land-dwelling creatures -- they have skin that protects them from drying out, and toes with claws. Some reptiles later adapted to life in the water; others took to the air.
Most reptiles are ectotherms or cold-blooded -- they use their environment to warm and cool their bodies.
Amphibians have four legs, and often look like reptiles. But amphibians, such as salamanders and frogs, have moist skin that does not protect them from drying out, and toes without claws. The eggs of amphibians are gelatinous and have no shell. Amphibians usually go to water or very moist places to breed and lay their eggs