Found in all continents but Antarctica, reptiles are a class of vertebrates that include crocodiles, alligators, lizards, snakes, turtles and tortoises. All reptiles are cold-blooded and their skin is covered with scales as opposed to feathers or fur. They range in size from tiny geckos measuring less than 2 cm in length to saltwater crocodiles that can reach 5.5 m in length and weigh more than 1,000 kg. Most reptile species lay eggs (oviparous); the embryo develops inside the egg and outside the mother’s body, without a larval stage. However, a small fraction of reptile species, including boas and most vipers, are ovoviviparous or viviparous and give birth to live young. Asexual reproduction has been identified in a few species of lizards and in one snake.
As ectothermic (cold-blooded) species, reptiles regulate their body temperature by moving into warmer or cooler environments in order to achieve optimal body temperature for different processes such as digestion or development of embryos. This means that reptiles lower dietary requirements and can consequently feed less frequently and to live longer than other endothermic (warm-blooded) animals.
The habitat of reptiles varies greatly and includes the open sea, coral reefs, mangroves, freshwater habitats and many terrestrial habitats from deserts to rainforests. As with amphibians, reptiles are often useful indicators of environmental change as they are very sensitive to ecological changes.