Ornithischia (extinct order) en

Extinct order of obligate bipedal or quadrupedal, beaked, herbivorous dinosaurs characterized by a pelvic structure like that of birds, a beak-like structure in the front part of the mouth and grinding teeth in the rear, a four-branched pelvis, toes that often have hooflike structures., and often having heavy armor and horns. Dating from the Upper Triassic to Upper Cretaceous, existed in five major groups: ornithopods, pachycephalosaurs, stegosaurs, ankylosaurs, and ceratopsina dinosaurs.