Reptiles, a various group of air-breathing vertebrates, are characterized by their scaly skin, amniotic eggs, and ectothermic (chilly-blooded) metabolism. They are customarily categorised into four residing orders: Crocodilia (crocodiles and alligators), Sphenodontia (tuataras), Squamata (lizards and snakes), and Testudines (turtles and tortoises).