THE SPECIES OF RHYNCHOSAURUS, A RHYNCHOSAUR (REPTILIA, DIAPSIDA) FROM THE MIDDLE TRIASSIC OF ENGLAND

The rhynchosaur Rhynchosaurus articeps Owen, 1842, from the Middle Triassic of Grinshill, northern Shropshire, England, was a small reptile, about 0.5 m long. About 17 individual animals are represented by skulls, complete skeletons and partial skeletons, and these have permitted detailed restorations. A further species of Rhynchosaurus from Warwick, named here R. brodiei, is represented by 15 specimens of partial skulls, tooth-bearing elements, and isolated postcranial bones. The third species of Rhynchosaurus from Devon, named here R. spenceri, is now known from numerous specimens of at least 25 individuals, most of which were collected recently. Each species is described. Teeth are not well preserved in R. articeps, but several specimens of R. brodiei and R. spenceri give detailed information. The diet was probably tough vegetation, which was dug up by scratch-digging. Rhynchosaurus is found variously in fluvial-intertidal deposits with evidence of desiccation and fluvial-aeolian deposits laid down in arid conditions with occasional flash floods. The bones have generally been transported. Rhynchosaurs are archosauromorph diapsids, possibly related to the enigmatic Trilophosaurus, and a sister group to Prolacertiformes + Archosauria. A cladistic analysis of Rhynchosauria reveals one major subgroup, the Hyperodapedontinae (Hyperodapedon and Scaphonyx), which is late Triassic in age. The specimens of Rhynchosaurus have been used as biostratigraphic indicators for the English middle Triassic, indicating Anisian to early Ladinian ages. The three species can be arranged in a sequence from "most primitive' to "most advanced', but this cannot be used confidently to give a stratigraphic sequence. -from Author