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