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 Marmoretta, Gephyrosaurus was a sister to the rest of the Rhynchocephalia (see below) beginning with the terrestrial Planocephalosaurus and the aquatic Ankylosphenodon and Palaeopleurosaurus.
Distinct from Marmoretta, the skull of Gephyrosaurus had a taller skull. The lacrimal was fused to the maxilla. The postorbital and squamosal were larger and deeper. The preorbital was larger. The fused parietal was shorter and posteriorly indented. All of the palatal elements had more tiny denticles.
Postcranially comparisons must be made to Palaegama and Saurosternon. The vertebrae were shorter. The pectoral girdle was much smaller and the limbs were smaller and more gracile. The pubis and ischium were separated by a thyroid fenestra. The manus and pes are unknown.
Gephyrosaurus nested at the base of the Rhynchocephalia, a clade with a living representative, Sphenodon the Tuatara. According to the large reptile tree, it also contains Trilophosaurus, Mesosuchus and the rhynchosaur, Hyperodapedon.