Thyreophora ("shield bearers", often known simply as "armored dinosaurs") is a group of armored ornithischian dinosaurs that lived 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 were herbivorous and had relatively small brains for their body size.
Thyreophora includes various subgroups, including the suborders Ankylosauria and Stegosauria. In both the suborders, the forelimbs were much shorter than the hindlimbs, particularly in stegosaurs. The clade has been defined as the group consisting of all species more closely related to Ankylosaurus than to Triceratops. Thyreophora is the sister group of Cerapoda within Genasauria.
Basal thyreophorans form a grade leading to Ankylosauria and Stegosauria,[1][2] or are instead sister to Ankylosauria with Stegosauria being more basal than either of them.[3]
These were small-to-medium size dinosaurs with small, primitive plates. Some of them are thought to have walked bipedally. The majority of these, such as Scelidosaurus, Scutellosaurus, Emausaurus, and Yuxisaurus are known from the Northern Hemisphere, in North America, Europe and China.
Among the Ankylosauria, the two main groups are the Euankylosauria (containing ankylosaurids and nodosaurids) and the Parankylosauria.[4]