The reptiles dominated the earth for a period of more than 150 million years. The modern survivors of the Age of Reptiles include the lizards, snakes, crocodiles, alligators, and turtles. In ancient times, the predominant reptiles were the dinosaurs. Reptiles belong to the class Reptilia.
Reptiles display a number of adaptations that support their life on land. They have a dry, scaly skin that retards water loss. The structural makeup of their limbs provides better support and allows reptiles to move more quickly than any of the amphibians.
Reproduction in reptiles occurs exclusively on land. The male places sperm into the body of the female, and the embryo develops within an egg, which is laid on dry land. Other reptilian characteristics pertain to the respiratory and circulatory systems. The lungs have a greater surface area than that of the amphibians and permit more air to be inhaled. The circulatory system includes a three‐chambered heart that separates oxygen‐rich and oxygen‐poor blood.