Reptiles (Encyclopedia of Science)
A reptile is an organism in the kingdom Animalia and the class Reptilia. (Kingdoms are the main divisions into which scientists classify all living things on Earth; kingdoms are further subdivided into phylums [or divisions], classes, and orders.) The reptiles include more than 6,000 species grouped into four orders: the turtles (Chelonia), the snakes and lizards (Squamata), the crocodiles and alligators (Crocodilia), and the tuataras (Sphenodonta), large lizardlike animals found only on islands off the coast of New Zealand.
A number of other reptilian orders are now extinct. These include some of the largest animals ever to occupy the planet. Examples include the fishlike ichthyosaurs, the long-necked plesiosaurs, and the huge flying and gliding pterosaurs. The most famous of the extinct reptilian orders were the dinosaurs, that included immense, ferocious predators such as Tyrannosaurus rex and enormously large herbivores (plant-eaters) such as Apatosaurus.
The first reptiles known in the fossil record lived about 340 million years ago. The last representatives of the dinosaurs became extinct about 65 million years ago, after being the dominant large animals of Earth for more than 250 million years.
Reptiles are extremely diverse in their form and function. They characteristically have four legs, although some groups such as the snakes...
(The entire section is 548 words.)
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