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