| ornithischian (ôr'nə-thĭs'kē-ən) Any of various dinosaurs belonging to the group Ornithischia, one of the two main divisions of dinosaurs. Ornithischians had a pelvis similar to that of modern birds (although birds are not descended from them), in which part of the pubis pointed backwards and parallel to the ischium. They also had a special bone in front of the lower jaw (called the predentary bone), and frequently had armor plating or bony outgrowths of the skull. Ornithischians comprise all the herbivorous dinosaurs except the sauropods, and include ankylosaurs, hadrosaurs, stegosaurs, and ceratopsians. Compare saurischian. |