Dinosaurs belonging to this order were particularly abundant during the
Jurassic and are characterized by hip bones that are similar to those of
modern lizards. These dinosaurs were first discovered in rocks of
Triassic age and did not become extinct until the end of the Cretaceous.
The lizard-hipped reptiles are divided into two rather specialized
groups of dinosaurs: the _theropods_ (carnivorous bipedal dinosaurs that
varied greatly in size) and the _sauropods_ (herbivorous, quadrupedal,
semi-aquatic, usually gigantic dinosaurs).