The Triassic reptiles Brachyrhinodon and Polysphenodon and the relationships of the sphenodontids

Abstract

Two Triassic sphenodontid reptiles, Brachyrhinodon taylori and Polysphenodon mulleri, are redescribed. Both genera are blunt-snouted forms but, as a result of distortion in the original fossils, the degree to which the snouts are shortened has previously been over-elaborated. An elongate temporal region and an interorbital width exceeding that of the parietal table are both derived characters in sphenodontids. Po!vsphenodon is plesiomorphic for both conditions, whereas Brachyrhinodon displays the derived states. Therefore, it is assumed that the reduced snout has been independently derived in each genus. The limb elements of Polysphenodon are long relative to the size of the skull and are similar in proportions to some species of Homoeosaurus. This resemblance is considered to be indicative of similar locomotory requirements rather than close evolutionary relationships. Ciadograms showing possible interrelationships within the Sphenodontida are based on twenty-nine character states.

Studies on continental Late Triassic tetrapod biochronology. I. The type locality of Saturnalia tupiniquim and the faunal succession in south Brazil

“…This taxon is mainly known from Jurassic strata (Evans and Kermack, 1994;Wu, 1994;Sues et al, 1994;Sues and Reisz, 1995), but its type species, C. hudsoni, comes from the Cromhall Quarry, a 'Fissure Fill' deposit in west England (Fraser, 1994), which is usually dated as Late Triassic (Walkden and Fraser, 1993;Benton and Spencer, 1995). In addition, according to Wu (1994), the outgroup to Clevosaurus seems to be Brachyrhinodon taylori, which comes from the Lossiemouth Sandstone Formation in Scotland (Benton and Walker, 1985;Fraser and Benton, 1989). This formation is considered coeval to the Hyperodapedon assemblage zone of the Santa Maria Formation (Ochev and Shishkin, 1989;Lucas, 1998) and older than the Triassic 'Fissure Fill' deposits of west England.…”

At the feet of the dinosaurs: the early history and radiation of lizards

“…3). Within Sphenodontia, the pleuroacrodont Upper Triassic Diphydontosaurus (Whiteside, 1986) is basal, with the fully acrodont Planocephalosaurus (Fraser, 1982) lying one node crownward (Fraser & Benton, 1989;Wilkinson & Benton, 1996). All higher taxa show a further reduction in the number of palatine tooth rows, a reduction in the total number of teeth, and evidence of either orthal or propalinal shear (e.g.…”

Studies on continental Late Triassic tetrapod biochronology. II. The Ischigualastian and a Carnian global correlation

“…Dicynodonts, procolophonids, traversodontids, and rhynchosaurs occur throughout the mid-late Triassic, whereas sphenodontians and prosauropods in the fauna suggest a Late Triassic age (Lucas, 1998a). The oldest records of these taxa (Fraser and Benton, 1989;Gauffre, 1993a;cf. Jalil and Knoll, 2002) come from strata that appear coeval with the Ischigualasto Formation.…”