from the Late Triassic.
Comments: generally used as the most exclusicve clade for the sphenodontian reptiles, equivalent to Order Sphenodontia MAK120707
Known from the Early Jurassic fissure infills of Wales
Comments: This small animal (25-30 cm long) has numerous primitive characters, and shows a number of lepidosauromorph and many lepidosaur synapomorphies . Variously classified as a basal squamate or near- squamate, or more often as a basal sphenodontian.
Graphic: Benton 1985
Sphenodontia Williston 1925
from the Late Triassic.
Comments: Benton 1985 recommends the name Sphenodontia in preference to Rhynchocephalia because the latter was used to include rhynchosaurs (which are archosauromorphs) and other taxa. With adoption of Gephyrosaurus as sister taxon to the remaining Sphenodontia, Rhynchocephalia was ressurrected for by Gephyrosaurus + Sphenodontia, and presumably also for any species closer to Sphenodon than to Lacertia (to use a stem based definition). Alternative terms such as Sphenodontoidea Nopcsa 1928 and Sphenodontida Estes 1983 have also been proposed, but Williston's name Sphenodontia has priority.
Rhaetian of England
late Triassic of England
several diagnostic sphenodontid characters. but differs from Sphenodon in having teeth on the palate, a broader parietal, an emarginated quadrate, a retroarticular process, an incomplete lower temporal bar (primitive/ancestral feature also in Gephyrosaurus), and precision shear bite Benton 1985 p.148. Planocephalosaurus presents Differs also from the clevosaurs which it otherwise resembles by the lack both the anterior process of the quadratojugal and squamosal-jugal contact Gauthier et al 1988 p.25 (i.e. incomplete lower temporal bar, in contrast to Sphenodon )
Comments: According to Reynoso 2000, Planocephalosaurus + Sphenodontidae share numerous synapomorphies to the exclusion of more basal taxa like Diphydontosaurus and Gephyrosaurus
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