The reptile group includes four orders of animals: the turtles, the crocodilians, the sphenodon and the order of squamates, which includes snakes and lizards. These animals have a body protected by scales or plates in common and lay eggs to give birth. They are also ectotherms, which means that they rely on their environment to maintain their body temperature. There are more than 10,000 species of reptiles in the world, most of which are lizards. It should be noted that scientists no longer consider this class relevant given the advances in cladistics, but it is still used in current language to simplify the classification.