what are reptiles

Reptiles are a diverse group of air-breathing vertebrates characterized by their special skin made up of scales, bony plates, or a combination of both. They include crocodiles, snakes, lizards, turtles, and tortoises. Reptiles are ectothermic, meaning they do not maintain a constant internal body temperature like birds and mammals. Instead, they rely on external sources of heat to regulate their body temperature. They breathe using lungs and have dry skin covered with scales or horny plates. Reptiles first appeared in the fossil record 315 million years ago and were the dominant animals during the Mesozoic era, which lasted for 270 million years until the extinction of the dinosaurs. The major groups of living reptiles include turtles, tuatara, lizards, snakes, and crocodiles, accounting for over 8,700 species. Reptiles are tetrapod vertebrates, meaning they either have four limbs or are descended from four-limbed ancestors. Most reptiles are oviparous, meaning they lay eggs, although some species are viviparous.