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a suborder of ornithischian dinosaurs that lived in the Jurassic and early Cretaceous. The early stegosaurs —scelidosaurs—apparently walked primarily on their hind legs; later forms returned secondarily to locomotion on four legs. The stegosaurs were massive (reaching 6 m in length) herbivorous animals with a comparatively small head. Powerful bony plates on the back and tail protected them against attack by such large predators as carnosaurs. The plates apparently developed during the transition to quadrupedal locomotion, which decreased the vulnerability of the body surface. The structure of the teeth suggests that stegosaurs were the ancestors of other four-legged ornithischian dinosaurs, beginning with the ankylosaurs. Stegosaurian remains have been found in North America, in Western Europe, and in North and East Africa. Reports of stegosaurian finds in Asia proved to be erroneous.