Extended Data Fig. 2: Extra information on the skull of E. sinensis (SMMP 000016).

a, b, X-radiograph and photograph of the skull in ventral view. c, d, Photograph and line drawing of the snout portion of the skull in right-lateral view, showing the ornamentation on the external surface of the edentulous premaxillae, the anterior portions of the right dentary and maxilla; the absence of teeth and the surface ornamentation suggest the presence of a rhamphotheca in E. sinensis in life. e, Close-up photograph of the posterior portion of the left maxilla, showing column-like pleurodont posterior teeth with blunt tips and the teeth deeply inset from the labial margin and ankylosed to the labial base, which differs from the subthecodont implantation in Eunotosaurus africanus and Pappochelys rosinae; the implantation pattern of the teeth is unknown for O. semitestacea, because the lingual side of the dentition is not exposed in the known specimens. New characters: ch. 273 (1), keratinous beak present, as indicated by surface ornamentation; ch. 274 (1), anterior end of the dentary edentulous; ch. 275 (1), dentary tooth number fewer than 30. d, dentary; l, lacrimal; m, maxilla; ob, orbit; pm, premaxilla.