The supraoccipital is a bone in the back of the braincase. The supraoccipital plate of mesosaurs, synapsids, and diadectomorphs is broad and extends farther laterally than the postparietal. Amniote skulls in palatal view. There is no foramen between these bones in diapsids, synapsids, and diadectomorphs. Anterior lateral maxillary foramen distinctly larger than other foramina.
Amniote skulls in lateral view.
The temporal emargination supports a tympanum in turtles, and the presence of a slender stapes in several anapsids suggests that a tympanum appeared fairly early in this group. The ectopterygoid bears a shagreen of small denticles in romeriids, early synapsids, and diadectomorphs. Stapedial dorsal process unossified. The stapes of most early romeriids, mesosaurs, synapsids, and diadectomorphs has an ossified dorsal process. Sacral ribs with narrow distal contact.