Tseajaia campi (Vaughn 1964) Early Permian 90 cm in length was considered a pre-amniote by previous workers, but here Tseajaia and the other diadectomorphs nest deep within the Lepidosauromorpha. Derived from a sister to Limonoscelis and Oedaleops, Tseajaia was a sister to Tetraceratops.
Distinct from Limnoscelis, the skull of Tseajaia had laterally expanded "horns' on the quadtratojugal and reduced the lateral expansion of the prefrontals. Similar to Oedaleops, the premaxilla was not deep. The supratemporal did not contact the postorbital, which was greatly reduced. The pineal opening was enlarged, as in Oedaleops. All but one maxillary tooth were reduced. As in Oedaleops, the supratemporal extended beyond the squamosal. The mandible was convex.
The cervicals were slightly elongated. The pelvis was relatively shallower.