Emerald Robinson: Hi, I'm Emerald Robinson, and in this What is video, we'll discuss the characteristics of reptiles. Reptiles are the group of cold-blooded, egg-laying animals that have scales or bony plates called scutes, for body covering.
All of the approximately 9700 reptiles known to science are classified in the Eukarya domain, since their cells have nuclei. They are in the class Reptilia in the animal kingdom, and are vertebrates, meaning that they have a backbone. Reptiles were the first terrestrial vertebrates, animals that were able to live entirely on land.
Reptiles lay eggs that do not require water, and instead have specialized membranes that serve to support, nourish, and protect their growing young. These so-called amniotic eggs are also produced by birds and mammals.
All reptiles have dry skin that is covered with either scales or scutes. These structures, made largely of a watertight protein called keratin, help prevent water loss. Reptiles also experience pulmonary breathing, meaning they, like birds and mammals, have lungs housed in a rib cage that enable them to get oxygen from the air.
Reptiles are cold-blooded, or ectothermic, since they rely on an outside source of heat to regulate their body temperature. They are also poikilothermic, as their body temperature goes up and down based on the temperature of their environment.
There are four groups of modern reptiles: turtles and tortoises, all of which have a body covered with a shell; lizards and snakes, which have a lower jaw not directly connected to their skull; alligators and crocodiles, the largest living reptiles, and tuataras, large lizardlike animals native only to areas around New Zealand.
The largest reptile that ever lived was possibly a mega-dinosaur called Amphicoelias, which measured about 200 feet in length and weighed about 270,000 pounds. This giant and other prehistoric reptiles went extinct about 65 million years ago.