An extinct order of herbivorous dinosaurs, including the genera Stegosaurus, Omosaurus, and their allies.

Clade of ornithischian dinosaurs, placed with the clade Thyreophora, characterized by osteoderms evident as spikes on the shoulder regions (parascapular spines) and dermal armor restricted to two rows of vertically oriented plates, parallel to but also lateral to the axial skeleton (parasagittal plates) or spikes.

Known colloquially as stegosaurs, the Stegosauria are a group of herbivorous dinosaurs of the Jurassic and Early Cretaceous Periods, being found mostly in the Northern Hemisphere, predominantly in what is now North America and China. Their geographical origins are unclear; the earliest stegosaurs have been found in China, although fragmentary material hails from southern England.