THECODONT

any member of an order (Thecodontia) of primitive archosaurs (ruling reptiles) that is thought to include the ancestral stock of all other archosaurs, including birds, all dinosaurs, pterosaurs (extinct flying reptiles), and crocodilians (members of the reptilian order that includes crocodiles, alligators, and caimans). The name thecodont means socket-toothed. The order has an extensive fossil record; thecodonts were distributed throughout the world during the Triassic Period (from 245 to 208 million years ago). There is a general trend toward a more upright stance. Some early thecodonts had four feet; others, however, had elongated hind legs, a modified hip structure, and other features that suggest they were becoming adapted to a bipedal mode of life.