Answer:

Most reptiles are ectotherms (cold-blooded): they maintain their body temperature by absorbing heat from the environment, so their body temperature changes with environmental temperature. In contrast, most mammals and birds are endotherms (warm-blooded): they are able to maintain a constant body temperature despite changes in the environmental temperature. Snakes, lizards, and chelonians have a 3-chambered heart. Crocodilians have a 4-chambered heart. Eggs are fertilized internally (inside the body). Some reptile species lay eggs from which the offspring hatch, and others give birth to live young.