Fig. 10 in An exceptionally preserved Sphenodon-like sphenodontian reveals deep time conservation of the tuatara skeleton and ontogeny

Fig. 10 Evolutionary changes on the temporal region of sphenodontians. Many early-evolving lepidosaurs retain a single temporal fenestration as the jugal (cyan) does not contact the quadrate/quadratojugal (green) posteriorly. Afull development of the lower temporal bar and double temporal fenestration evolved independently at least twice in sphenodontians, once among clevosaurids and once in sphenodontines—an adaptation for stabilizing the quadrate and reducing overall stress in the skull during hard biting58. The latter is unique among lepidosaurs by including contributions from both the jugal and quadratojugal—a morphology convergent with many non-lepidosaurian early diapsid reptiles. Red circle, complete lower temporal bar; blue circle: incomplete lower temporal bar; blue-red gradient circle, lower temporal bar incomplete in juveniles but complete in adults. Skull drawings from top to bottom: Gephyrosaurus (drawn by TRS based on ref. 20), Megachirella (re-drawn by TRS from ref. 33), Diphydontosaurus (drawn by TRS based on ref. 20), Clevosaurus (drawn by TRS based on ref. 20), Palaeopleurosaurus (drawn by TRS based on ref. 20), Navajosphenodon (drawn by A. Brum), and Sphenodon (drawn by TRS based on MCZ R4702).