Mesozoic terrestrial reptiles with upright gait.

Any of the Mesozoic reptiles belonging to the groups designated as ornithischians and saurischians.

The now extinct carnivorous or herbivorous reptiles of the Mesozoic era (208 million to 144 million years ago), sometimes referred to as the Jurassic; dinosaurs survived for more than 180 million years.

n. Phylum Chordata, Class Reptilia The common name given to any of certain extinct archosaur reptiles, often very large, that thrived worldwide for some 150 million years and died out at the end of the Mesozoic Era, about 65 million years ago.