Sisteronia

Sisteronia seeleyi, basicranium. A, B: basisphenoid (RGHP SI 2) in dorsal (A) and ventral (B) views. C: basioccipital (CAMSM B57943) in posterior view. D: holotype basioccipital (CAMSM B58257_67) in dorsal view. E–G: supraoccipital (RGHP SI 2) in posterior (E) and anterolateral (otic) (F, G) views. H–J: left opisthotic (CAMSM B58257_67) in posterior (H) and anterior (otic) (I, J) views. K: left stapes (RGHP SI 2) in posterior view. Note the extremely reduced (nearly absent) extracondylar area of the basioccipital, a platypterygiine synapomorphy, and the dorsal process posterior to a triangular depression (delineated by the thick dotted line) on the basioccipital, an autapomorphy of Sisteronia seeleyi. Abbreviations: AVSC: impression of the anterior vertical semicircular canal of the otic labyrinth; HSC: impression of the horizontal semicircular canal of the otic labyrinth; PVSC: impression of the posterior vertical semicircular canal of the otic labyrinth; UPL: impression of the utricular portion of the otic labyrinth; Vag: vagus foramen.