The formal scientific name for the horned dinosaurs is Ceratopsia (sera-top-see-a) and all lived during the Cretaceous Period. Most members of the group have prominent horns located in the nasal region and often over the eyes as well. Another distinguishing character is a prominent frill that extends from the back of the head and projects over the neck region. Scientists believe that powerful jaw muscles were attached to this frill allowing the jaws to close with considerable force. In advanced members of the group, there were batteries of teeth that slid past each other in a scissor-like fashion, suggesting a diet of very tough, fibrous vegetation.
Horned dinosaurs (ceratopsians) are further distinguished from other dinosaurs by having a peculiar parrot-like beak. The upper part of the beak is formed by a bone that is not found in any other creature. This is the rostral bone (see illustration). The lower part of the beak is formed by the predentary, a bone that is found in all other bird-hipped dinosaurs, but is unique to that group (see picture on page concerning kinds of dinosaur).
Horned dinosaurs generally walked on all fours (they were quadrupeds), but evolved from two-legged (bipedal) ancestors. Psittacosaurus (sit-tack-oh-soar-us) from the Middle Cretaceous of Mongolia is the earliest known ceratopsian and the only one to retain a bipedal posture. It was small in size (5 feet long) and lacked the characteristic frill and horns that so prominently mark the other members of the group. Features on the skull of Psittacosaurus indicate that it was closely related to the odd "bone-headed" dinosaurs known as Pachycephalosaurs (Packy-seff-ah-lo-soars). Psittacosaurus means "parrot lizard," alluding to its distinct parrot-like appearance.
The navigation bar to your left will lead you to pages that discuss individual horned dinosaurs.