What makes an ornithischian dinosaur? All terrestrial animals and marine animals derived from terrestrial stock have hip girdles, or pelvises, and all hip girdles are composed of three bones: the ilium, ischium, and pubis. All ornithischians are united by a pubis pointing backward, running parallel with the ischium. The name "Ornithischia" means "bird-hipped," and birds also have pelvises in which the pubis points backwards. However, birds are more closely related to the Saurischia, or "lizard-hipped" dinosaurs, than to the ornithischian dinosaurs featured on this page.
The hip girdle of a typical ornithischian dinosaur is enlarged in the diagram at right. In the diagram, the pubis is pale orange, the ilium is red, and the ischium is brown.
There were many kinds of ornithischian dinosaurs, dating back to the early Jurassic. There were the Heterodontosauridae, early ornithischians; the Ornithopoda, which included hypsilophodontids,the hadrosaurs ("duck-billed" dinosaurs) and Iguanodontia; Marginocephalia, containing the Ceratopsia, or horned dinosaurs, and the thick-skulled Pachycephalosauria; and the Thyreophora, the armored dinosaurs.
Explore these UCMP pages on ornithischian dinosaurs:
Original page created by Dave Polly circa 1994, with later modifications by Rob Guralnick and Ben Waggoner; modifications since 2005 by David Smith.