Reptiles, a diverse group of air-respiration vertebrates, are characterized by their scaly skin, amniotic eggs, and ectothermic (cold-blooded) metabolism. They can be ordinarily classified into four dwelling orders: Crocodilia (crocodiles and alligators), Sphenodontia (tuataras), Squamata (lizards and snakes), and Testudines (turtles and tortoises)