Eothyris parkeyi (Romer 1937) Sakmarian, Early Permian ~290 mya, ~6 cm skull length, was derived from a sister to Oedaleops and was a sister to Casea. Earlier workers placed Eothyris at the base of the Synapsida along with the caseids. Here, Eothryis, Oedaleops and Casea are not related to synapsids. Instead they nest closer to Milleretta and Concordia and Romeria primus.
Distinct from Oedaleops, the skull of Eothyris had only two caniniform teeth and these were thicker at their bases. The jugal did not descend. The lateral temporal fenestra was smaller chiefly due to a deeper jugal. The skull roof was slightly concave. The quadrate leaned anteriorly.