Reptiles, a diverse group of air-respiration vertebrates, are characterized by their scaly skin, amniotic eggs, and ectothermic (chilly-blooded) metabolism. They're usually categorised into four living orders: Crocodilia (crocodiles and alligators), Sphenodontia (tuataras), Squamata (lizards and snakes), and Testudines (turtles and tortoises). big