Reptiles include snakes, lizards, crocodilians, and turtles. Reptiles are cold-blooded.
Most reptiles are egg-layers, although some produce live young.
In cold regions, reptiles hibernate. In extremely hot or dry climates, some reptiles will estivate, or go into a torpor. Because they lack intenal heating mechanisms, reptiles depend on external heat sources. Thus, you will often find them lying in the sun on rocks and logs. Most reptiles have a three-chambered heart.