Gephyrosaurus bridensis (Evans 1980, 1981) Early Jurassic, 10 cm snout-to-vent length was a basal rhynchocephalian (= sphenodontid) that probably originated in the Permian. Derived from a sister to Paliguana and Saurosternon, Gephyrosaurus was a sister to the rest of the Rhynchocephalia (see below). Lacertulus , Homoeosaurus and Iguana were sister taxa at the base of the Squamata.
Distinct from Paliguana, the skull of Gephyrosaurus had a taller and narrower skull. The lacrimal was fused to the maxilla. The postorbital and squamosal were larger and deeper. The preorbital was smaller. The jawline was straight. The parietals were narrower. Teeth continued to the posterior orbit.
Distinct from Owenetta, in palatal view, the palatine was slightly smaller creating a larger suborbital fenestra and the pterygoids were more gracile creating a larger interpterygoid opening. The ectopterygoid was distinct from the palatine, separated by a suborbital fenestra. All of the palatal elements had more tiny denticles. The cervicals were longer and more robust.
Distinct from Saurosternon the girdles and limbs were smaller. The pubis and ischium were separated by a thyroid fenestra. The manus and pes are unknown.