Like the spikes and shields of ankylosaurs, the bony plates and spines of stegosaurians evolved from the low-keeled osteoderms characteristic of basal thyreophorans. One such described genus, "Scelidosaurus", is proposed to be morphologically close to the last common ancestor of the clade uniting stegosaurians and ankylosaurians, the Eurypoda. Galton (2019) interpreted plates of an armored dinosaur from the Lower Jurassic (Sinemurian-Pliensbachian) Lower Kota Formation of India as fossils of a member of Ankylosauria; the author argued that this finding indicates a probable early Early Jurassic origin for both Ankylosauria and its sister group Stegosauria. Footprints attributed to the ichnotaxon "Deltapodus brodricki" from the Middle Jurassic (Aalenian) of England represent the oldest probable record of stegosaurians reported so far. Outside that, there are assigned fossils to stegosauria from the Toarcian: the specimen "IVPP V.219", a chimaera with bones of the sauropod "Sanpasaurus" is known from the Maanshan Member of the Ziliujing Formation. The perhaps most basal known stegosaurian, the four-metre-long "Huayangosaurus", is still close to "Scelidosaurus" in build, with a higher and shorter skull, a short neck, a low torso, long slender forelimbs, short hindlimbs, large condyles on the thighbone, a narrow pelvis, long ischial and pubic shafts, and a relatively long tail. Its small tail club might be a eurypodan synapomorphy. "Huayangosaurus" lived during the Bathonian stage of the Middle Jurassic, about 166 million years ago.