Eothyris parkeyi (Romer 1937) Sakmarian, Early Permian ~290 mya, ~6 cm skull length, was derived from a sister to Milleretta RC70 and was a sister to Oedaleops. Colobomycter was derived from Eothyris. 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.

Distinct from Milleretta, the skull of Eothyris was lower and leaned anteriorly, from the orbit to the quadrate. A lateral temporal was present. The jugal did not descend. The quaratojugal contacted the maxilla. The prefrontal contacts the postfrontal. The postparietals were visible dorsally. The skull roof was slightly concave. There were two sets of caniniform teeth.

Oromycter dolesorum (Reisz 2005, latest Early Permian, Leonardian) is a basal caseid represented by a few skeletal parts, all superbly preserved. It is more primitive than other caseids in that it lacks leafy tooth serrations, has a longer lacrimal (naris-orbit distance) and a larger number of marginal teeth.

Reisz R 2005. Oromycter, a new caseid from the lower Permian of Oklahoma. Journal of Vertebrate Paleontology 25(4):905-910.

Romer AS 1937. New genera and species of pelycosaurian reptiles. Proceedings of the New England Zoological Club 16:89–96.

Robert RR, Godfrey SJ and Scott D 2009. Eothyris and Oedaleops: Do These Early Permian Synapsids from Texas and New Mexico form a Clade?Journal of Vertebrate Paleontology 29(1):39-47. doi: 10.1671/039.029.0112

wiki/Eothyris