Reptiles are cold-blooded vertebrate animals that lay eggs and have scales or plates on their skin. Though all cellular metabolism produces some heat, modern reptiles do not generate enough to maintain a constant body temperature and are thus referred to as "cold-blooded." They are found on every continent except for Antarctica, although their main distribution comprises the tropics and subtropics. Almost all reptiles are covered by scales and most are egg-laying. Reptiles are tetrapods and amniotes, animals whose embryos are surrounded by an amniotic membrane.
Amphibians are a class of animals that include all tetrapods (four-legged vertebrates) that do not have amniotic eggs. They live both on land and in water but must lay their eggs in water. The name is derived from the Greek word amphibios which means "living a double life," as they spend part of their time on land and part in the water. There are about 5,700 living species of amphibians.
A herpetologist is a zoologist who studies reptiles and amphibians, and he has plenty to study! There are 23 species of crocodiles, caimans and alligators; 2 species of tuataras, 7,600 species of lizards, snakes and the like, and approximately 300 species of turtles.
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