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Crocodilians, turtles, snakes, lizards, amphisbaenians, and tuatara are all members of the Class Reptilia. These diverse groups have in common such traits as phi keratins in the skin and internal fertilization. These groups also have in common a mode of body temperature regulation called ectothermy, in which energy from the external environment, rather than large quantities of internal metabolic heat, are primarily used to elevate body temperature.
Scientific studies with reptiles have led to key contributions across biological disciplines. Developmental biology, genetics, ecology, molecular biology, and medicine have all advanced from the study of reptiles. The great diversity of sex-determining mechanisms (how males and females are made; e.g., gametes or temperature) that reptiles exhibit make them ideal subjects for evolution and ecology studies. For medicine, chemicals extracted from snake venom have been used to treat such ailments as high blood pressure, hemorrhage, and stroke.
Reptiles demonstrate amazing diversity in size, shape, and color. This diversity allows reptiles to occupy ecosystems as widely varying as oceans, deserts, grasslands, ponds, streams, and tropical forests. Learn more below about the groups that make up the world's 8,000+ reptile species.
Taxonomy--the biological field of classifying organisms--typically relies on systematics--the study of the relationships between living things. Visit other NBII Web pages to learn the basics of the organization of diversity and to find resources about taxonomy and systematics covering all forms of life.