Teyumbaita sulcognathus (formerly Scaphonyx sulcognathus Mantefeltro, Langer and Schultz 2010; Late Triassic, Brazil; UFRGS-PV-0232T) is a rhynchosaur related to Hyperodapedon. Note the deeply sculptured jugals, the dorsal orbits and fused maxilla/palatine creating a groove for the dentary teeth to slide against.

Hyperodapedon fischeri (Huxley 1859) Late Triassic, ~210 mya, ~1.3 m in length was a member of the Rhynchosauria, characterized by their weirdly wide skulls and protruding premaxillae. Romer (1956) considered rhynchosaurs and sphenodontians to be related, but Benton (1985) and Carroll (1988) mistakenly split them apart by placing too much emphasis on the lack of fusion in the teeth and tarsus rather than considering the suite of characters that more parimoniously unites them. Derived from a sister to Mesosuchus and Priosphenodon, Hyperodapedon and the rest of the rhynchosaurs became extinct at the end of the Triassic.

Distinct from Kaikaifilusaurus, the skull of Hyperodapedon was much wider posteriorly. The premaxilla protruded further. The maxilla was much deeper. The lower temporal bar was complete, retaining a lateral temporal fenesta. Several rows of teeth lined the jaws and palate. The mandible was deeper anteriorly.

Distinct from Mesosuchus, the neural spines of the cervicals leaned posteriorly. The dorsal ribs were robust and strongly curved to enclose a large gut.

The scapula and coracoid were not fused. Large claws tipped each finger.

The pelvis was longer. The ilium had an anterior process equal to the posterior one. The feet had tall claws and short, square (in dorsal view) phalanges. Digit V was a vestige.

A selection of rhynchocephalians compared to archosauriformes. Originally rhynchosaurs, like Hyperodapedon, were associated with rhynchocephalians (sphenodontians) like Brachyrhinodon. However the lack of fusion in the ankles of rhynchosaurs caused Cruickshank (1972) and Benton (1983) to consider rhynchosaurs close to archosaurs, like Prolacerta and Proterosuchus. Carroll (1988) considered this valid in his landmark textbook and Dilkes (1998) agreed.

The present tree found more parsimony nesting Hyperodapedon, Mesosuchus and Trilophosaurus with Brachyrhinodon, invalidating the archosaur-sister hypothesis. In the figure above, the overall morphologies of Hyperodapedon, Mesosuchus and Trilophosaurus share more traits with Brachyrhinodon than with Youngina, Prolacerta or Proterosuchus, as also demonstrated by the large reptile tree.

The palates of various rhynchocephalians. Bones colorized. Click to enlarge. In Mesosuchus the palatine is reduced and has lost its teeth. In Hyperodapedon the palatine retains teeth and extends lateral to the choanae to contact the premaxilla. In Howesia the palatine fuses to the maxillary tooth plate. In Trilophosaurus the palatine likewise fuses to the maxillary tooth plate and the palatine teeth fuse to the maxillary teeth, creating laterally elongated teeth with three lateral cusps.

Benton MJ 1983. The Triassic reptile Hyperodapedon from Elgin, functional morphology and relationships. Philosophical Transactions of the Royal Society of London, Series B, 302, 605-717.

Benton MJ 1990. The Species of Rhynchosaurus, A Rhynchosaur (Reptilia, Diapsida) from the Middle Triassic of England. Philosophical transactions of the Royal Society, London B 328:213-306. online paper

Benton MJ 1985. Classification and phylogeny of diapsid reptiles. Zoological Journal of the Linnean Society 84: 97-164.

Carroll RL 1988. Vertebrate Paleontology and Evolution. WH Freeman and Company.

Cruickshank ARI 1972. The proterosuchian thecodonts. In Studies in Vertebrate Evolution (ed. Jenkins KA and Kemp TS) 89-119. Edinburgh: Oliver and Boyd.

Dilkes DW 1995. The rhynchosaur Howesia browni from the Lower Triassic of South Africa. Paleontology 38(3):665-685.

Huxley TH 1859. Postscript to, R. I. Murchinson. On the sandstones of Morayshire (Elgin and c.) containing reptile remains; and their relations to the Old Red Sandstone of that country. Quarterly Journal of the Geological Society, London, 15, 138-152.

Huxley TH 1869. On Hyperodapedon. Quarterly Journal of the Geological Society, London, 25, 138-152.

Huxley TH 1887. Further observations upon Hyperodapedon gordoni. Quarterly Journal of the Geological Society, London, 43, 675-694.

Mantefeltro FC, Langer MC and Schultz CL 2010. Cranial anatomy of a new genus of hyperodapedontine rhynchosaur (Diapsida, Archosauromorpha) from the Upper Triassic of southern Brazil. Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 101: 27–52.

Romer AS 1956. Osteology of the Reptiles. University of Chicago Press, Chicago.

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