Reptiles have been around for 300 million years, and during the age of the dinosaurs, they ruled the Earth. Those days are long gone, and those giants have vanished, but some 6,500 species of reptiles still thrive today. Crocodiles, snakes, lizards, and turtles are all reptiles. Most reptiles live on land, and most lay eggs. They are vertebrates, and, unlike any other animals, are covered in scales. They are cold-blooded, and regulate their body temperature by seeking or avoiding the sun's heat.