Horned, ornithischian (bird-hipped) dinosaurs, which had beak-like jaws, from the Upper Cretaceous. The head accounted for about one-third of the total length of the body because of the development of a large, bony frill which protected the neck and shoulders. Triceratops is perhaps the best-known member of the group. It was 5–6 m long and had three forward-projecting horns, one over each eye and the third over the nose.