Hypsognathus fenneri (Gilmore 1928, Latest Triassic) skull width up to 12.5 cm is widely and correctly regarded as the most derived procolophonid. Procolophon was more primitive. Pentaedrusaurus was a sister taxon.

Here the dorsally open orbit extends deeply into the parietal, posterior to the pineal opening. Presumeably the eyeball occupied only the anterior half of this opening with jaw muscles filling the rest. The quadratojugal is ornamented with "horns."

Gilmore CW 1928. New Fossil Reptile from the Triassic of New Jersey. Proceedings of the United States National Museum 73(7):1-8

Owen R 1876. Descriptive and Illustrated Catalogue of the Fossil Reptilia of South Africa in the Collection of the British Museum. London, British Museum (Natural History).

Saila LK 2010. Osteology of Leptopleuron lacertinum Owen, a procolophonoid parareptile from the Upper Triassic of Scotland, with remarks on ontogeny, ecology and affinities. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 101, 1–25, 2010

Sues H-D, Olsen PE, Scott DM and Spencer PS 2000. Cranial Osteology of Hypsognathus fenneri, a Latest Triassic Procolophonid Reptile from the Newark Supergroup of Eastern North America. Journal of Vertebrate Paleontology, 20(2):275-284.