Reptiles, a various group of air-respiration vertebrates, are characterized by their scaly skin, amniotic eggs, and ectothermic (cold-blooded) metabolism. These are traditionally categorised into 4 dwelling orders: Crocodilia (crocodiles and alligators), Sphenodontia (tuataras), Squamata (lizards and snakes), and Testudines (turtles and tortoises).