| While many kinds of reptiles once dominated the Earth, only four orders have living representatives. The largest of these groups is the Squamata, which includes lizards and snakes. Turtles and tortoises belong to the order Chelonia, and crocodiles, alligators, caimans, and gavials belong to the order Crocodilia. The tuatara, often called a living fossil, is the only extant member of the order Rhynchocephalia. Prominent among extinct reptiles were the Saurischians (Tyrannosaurus and other “reptile-hipped” bipedal carnivores), which may have been the ancestors of birds, and the Ornithischians (“bird-hipped” herbivores such as Stegosaurus and Hypsilophodon). Mammals arose from the Therapsid line. |
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