Graphical live reconstruction of Eothyris

  • Archer County (Texas, USA)
  • Eothyris parkeyi

Eothyris is an extinct genus of synapsids from the family of Eothyrididae. The holotype and the same time the only known copy of the single species Eothyris parkeyi is a skull from the Petrolia Formation ( at the time Belle Plains Formation) of the Permian of North Texas, which was scientifically described by Alfred Romer in 1937. The most closely related genus is Oedaleops.


The skull of Eothyris is about 6 cm long. The body reached a length of less than 1 m. The upper jaw was equipped with two large eckzahnartigen teeth that had no counterpart in the lower jaw. Similar types of teeth were formed significantly smaller in Oedaleops, although this had a comparable size. From the construction of the remaining teeth can conclude that Eothyris was an insectivore.


Eothyris forms with Oedaleops the family of Eothyrididae. This is considered to be the sister taxon Caseidae, a group of herbivorous, medium-sized synapsids with a barrel-shaped body. The Eothyrididae and Caseidae are called Caseasauria, which are considered the basalste Synapsidengruppe as well as the sister taxon of Eupelycosauria. The Eupelycosauria, the more basal groups are referred to together with the Caseasauria as " Pelycosaurier " include, among other things, the famous " back sailing synapsids " as Dimetrodon and Edaphosaurus and mammals. The below cladogram shows the position of Eothyris within the Caseasauria (after Maddin et al, 2008 and Reisz et al, 2009. ).: