Reptiles are cold-blooded vertebrate animals that are covered in scales or scutes, and typically lay eggs. There are approximately 8,225 species of reptiles including crocodiles, gavials, caimans, alligators, tuatara, lizards, snakes, turtles, tortoises, and terrapins. Reptiles range in size from the smallest tiny gecko to the largest saltwater crocodile. Factors such as habitat loss, infectious diseases, introduced species, and pollution, and climate disruption threaten many reptile species with extinction.