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

1989; Oxford University Press; Volume: 96; Issue: 4 Linguagem: Inglês

10.1111/j.1096-3642.1989.tb02521.x

1096-3642

Nicholas C. Fraser, Michael J. Benton,

Ichthyology and Marine Biology

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. Polysphenodon 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. Cladograms showing possible interrelationships within the Sphenodontida are based on twenty-nine character states.