Rhynchosaurus articeps (Owen 18942) 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, Rhynchosaurus and the rest of the rhynchosaurs became extinct at the end of the Triassic. Hyperodapedon was more derived.
Distinct from Priosphenodon, the skull of Rhynchosaurus 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.