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 cold-blooded, meaning they do not maintain a constant internal body temperature and instead rely on their environment to regulate their body temperature. They are known for their ability to move into the sun or shade as needed to regulate their body temperature. Reproduction in reptiles also depends on temperature, with some species laying eggs and others giving birth to live young.
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. Today, reptiles are classified into four orders: Testudines (turtles), Crocodilia (crocodilians), Squamata (lizards and snakes), and Rhynchocephalia (the tuatara) . There are about 12,000 living species of reptiles listed in the Reptile Database as of May 2023.
Reptiles are most easily recognized by their dry, scaly skin, and they are mostly cold-blooded, with most species laying eggs, although some give birth to live young. The United States is home to a diverse range of reptiles, but many reptile species face threats such as habitat destruction, pollution, and overexploitation. Some reptile species, such as the Kemp’s ridley sea turtle and the Puerto Rican boa, are currently categorized as endangered under the U.S. endangered species list.
