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:
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|---|---|
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Synapsida |
| Family: | †Sphenacodontidae |
| Genus: | †Eosyodon Olson, 1962 |
| Species: | †E. hudsoni
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| Binomial name | |
| †Eosyodon hudsoni Olson, 1962
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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.
See also edit
References edit
- ^ Olson 1962, pp. 59–60.
- ^ Olson 1962, p. 48.
- ^ Sidor & Hopson 1995.
- ^ Kammerer 2011, p. 291.
- ^ Olson 1962, p. 9.
- ^ DiMichele et al. 2001.
- ^ Lucas & Golubev 2019.
Bibliography edit
- DiMichele, William A.; Mamay, Sergius H.; Chaney, Dan S.; Hook, Robert W.; Nelson, W. John (2001). "An Early Permian flora with Late Permian and Mesozoic affinities from North-Central Texas". Journal of Paleontology. 75 (2): 12.
- Kammerer, Christian F. (2011). "Systematics of the Anteosauria (Therapsida: Dinocephalia)". Journal of Systematic Palaeontology. 9 (2): 261–304. doi:10.1080/14772019.2010.492645. ISSN 1477-2019.
- Lucas, Spencer G; Golubev, Valeriy K (2019). "Age and duration of Olson's Gap, a global hiatus in the Permian tetrapod fossil record". Permophiles. 67: 20–23. ISSN 1684-5927.
- Olson, Everett C. (1962). "Late Permian Terrestrial Vertebrates, U. S. A. and U. S. S. R." Transactions of the American Philosophical Society. 52 (2): 1–224. doi:10.2307/1005904. ISSN 0065-9746. JSTOR 1005904.
- Sidor, C. A.; Hopson, J. A. (1995). "The taxonomic status of the Upper Permian eotheriodont therapsids of the San Angelo Formation (Guadalupian), Texas". Journal of Vertebrate Paleontology. 15 (3A): 53A.