Eosyodon

Eosyodon is a dubious genus of extinct non-mammalian synapsids from the Permian of Texas. Its type and only species is Eosyodon hudsoni. Though it was originally interpreted as an early therapsid, it is probably a member of Sphenacodontidae, the family of synapsids that includes Dimetrodon.

Eosyodon Temporal range:
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Synapsida
Family:	†Sphenacodontidae
Genus:	†Eosyodon Olson, 1962
Species:	†E. hudsoni
Binomial name
†Eosyodon hudsoni Olson, 1962

Eosyodon hudsoni was named by Everett C. Olson in 1962 on the basis of fragmentary material from the San Angelo Formation in Texas.[1] The species name honors J. Hudson, a ranch foreman who aided Olson's work. A femur, currently cataloged as FMNH UR 575, was designated the holotype, and skull fragments, partial ribs, and a few other bones were also assigned to the species. Olson interpreted Eosyodon as a therapsid closely related to Syodon, and assigned both genera to the family Brithopodidae of the infraorder Eotheriodontia. Eotheriodonta was a new taxon defined by Olson in the same paper, to encompass several taxa he regarded as a group of therapsids intermediate between pelycosaurs and later therapsids.[2]

In 1995, C. A. Sidor and J. A. Hopson presented a reevaluation of Olson's eotheriodonts at the annual conference of the Society of Vertebrate Paleontology, and concluded that they were based on caseid and sphenacodontid pelycosaurs.[3] In 2011, Christian Kammerer agreed with their evaluation and concluded that Eosyodon was a sphenacodontid.[4] He regarded Eosyodon as a nomen dubium.

Olson regarded the San Angelo fauna, including Eosyodon, as being from the early Guadalupian, chronologically equivalent to the Kazanian therapsid fauna of Russia.[5] However, the San Angelo Formation is now regarded as belonging to the Kungurian stage of the Permian.[6][7] As such, Eosyodon is somewhat older than the earliest definitive therapsids.