The Thyreophora, often known simply as "armored dinosaurs", were a subgroup of the ornithischian dinosaurs. They were armored dinosaurs, living from the early Jurassic until the end of the Cretaceous. Thyreophorans are characterized by the presence of body armor lined up in longitudinal rows along the body. Primitive forms had simple, low, keeled scutes or osteoderms, whereas more derived forms developed more elaborate structures including spikes and plates. Most thyreophorans had relatively small brains for their body size. Thyreophorans include various subgroups, including the suborders Ankylosauria and Stegosauria. In both the suborders, the forelimbs were much shorter than the hindlimbs, particularly in stegosaurs.