Eothyris

Eothyris is a genus of extinct synapsid belonging to the order Pelycosauria. It is classified within the suborder Eothyrisoidea, a group of early pelycosaurs that existed during the Early Permian period. The genus is known from a single species, Eothyris profunda. Fossils of Eothyris have been found in the Wichita Group of Oklahoma, United States.

Eothyris was a relatively small pelycosaur, with an estimated skull length of around 10 centimeters. Its most distinctive feature was its unusually large orbits, or eye sockets, which suggest it may have had excellent vision, possibly adapted for low-light conditions. The skull lacked temporal fenestrae, a characteristic of the early pelycosaurs and other basal synapsids. Its teeth were small and pointed, indicating a diet likely consisting of insects or other small invertebrates.

The phylogenetic placement of Eothyris within pelycosauria has been a subject of debate. It is considered a primitive member of the Eothyrisoidea, a clade that may have given rise to more derived pelycosaur groups. The Eothyrisoidea themselves are placed within the larger group Synapsida, which includes all mammals and their extinct relatives. The discovery of Eothyris has contributed to our understanding of the early evolution of synapsids and the diversification of pelycosaurs during the Permian.