One of "Westlothiana's" autapomorphies (unique features) of the skull is the fact that the postfrontal bones, which typically occupy the upper rear corner of the orbits, are very elongated. They stretch forward to form almost the entire upper rim of the eye sockets, and possibly contact the prefrontal bones at the front edge of each socket. This level of contact is uncertain, and may be so slight that it can occur on one side of the skull and not the other. Nevertheless, the possession of any amount of contact between the prefrontal and postfrontal is a primitive feature lost by true amniotes.