Opisthias

Opisthias Temporal range: Kimmeridgian–Tithonian PreꞒ Ꞓ O S D C P T J K Pg N Possible Berriasian record
Jaw of Opisthias rarus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Rhynchocephalia
Clade:	†Opisthodontia
Genus:	†Opisthias Gilmore 1909
Type species
Opisthias rarus Gilmore, 1905[1]

Opisthias is a genus of sphenodont reptile. The type species, Opisthias rarus, is known from the Late Jurassic (Kimmeridgian-Tithonian) of western North America.^[2][3]

Distribution

Opisthias is primarily known from remains found in the Late Jurassic of the United States, with remains found in the Morrison Formation (Colorado, Utah, and Wyoming),^[2][3][1] present in stratigraphic zones 2 and 4–6.^[4] Other remains suggested to be closely related to Opisthias are also known from the Late Jurassic Alcobaça Formation of Portugal.^[5][6] An undescribed crushed skull (DINO 16454) from the Morrison Formation has been attributed to this genus by some sources, though this has been strongly disputed by others.^[7]

A lower jaw is also known from the Berriasian aged Lulworth Formation of the United Kingdom, which appears to be distinct from the type North American species.^[8] A fragmentary dentary possibly attributable to Opisthias is also known from the Berriasian aged Angeac-Charente bonebed in France.^[9]

Diet

Opisthias has been interpreted as a generalist, with its tooth morphology indicating had an ability to process plant material.^[10]

See also

• Prehistoric reptile
• Paleobiota of the Morrison Formation

References

1. "Opisthias Gilmore 1909 (rhynchocephalian)". Paleobiology Database.
2. Foster J (2007). "Table 2.1: Fossil Vertebrates of the Morrison Formation.". Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press. pp. 58–59.
3. Herrera-Flores, J.A.; Stubbs, T.L.; Sour-Tovar, F. (2022). "Redescription of the type specimens for the Late Jurassic rhynchocephalian Opisthias rarus and a new specimen of Theretairus antiquus from Quarry 9, Morrison Formation, Wyoming, USA". Acta Palaeontologica Polonica. 67 (3): 623–630. doi:10.4202/app.00929.2021.
4. Foster J (2007). "Appendix". Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press. pp. 327–329.
5. Herrera-Flores JA, Stubbs TL (July 2018). "A re-evaluation of the taxonomy and diversity of the Late Jurassic sphenodontian Opisthias rarus Gilmore 1909 (Lepidosauria: Rhynchocephalia)[oral presentation]". 13th Symposium on Mesozoic Terrestrial Ecosystems and Biota.
6. Malafaia, E.; Ortega, F.; Escaso, F.; Dantas, P.; Pimentel, N.; Gasulla, J. M.; Ribeiro, B.; Barriga, F.; Sanz, J. L. (2010). "Vertebrate fauna at the Allosaurus fossil-site of Andrés (Upper Jurassic), Pombal, Portugal". Journal of Iberian Geology. 36 (2): 193–204. Bibcode:2010JIbG...36..193M. doi:10.5209/rev_JIGE.2010.v36.n2.7. ISSN 1698-6180.
7. DeMar, David G.; Jones, Marc E. H.; Carrano, Matthew T. (2022-12-31). "A nearly complete skeleton of a new eusphenodontian from the Upper Jurassic Morrison Formation, Wyoming, USA, provides insight into the evolution and diversity of Rhynchocephalia (Reptilia: Lepidosauria)". Journal of Systematic Palaeontology. 20 (1): 2093139. doi:10.1080/14772019.2022.2093139. hdl:2440/136608. ISSN 1477-2019.
8. Herrera-Flores J (2020). Randall C (ed.). "New insights on an enigmatic sphenodontian jaw from Dorset". Proceedings of the Dorset Natural History and Archaeological Society. 141: 41–43.
9. Ronan Allain, Romain Vullo, Lee Rozada, Jérémy Anquetin, Renaud Bourgeais, et al.. Vertebrate paleobiodiversity of the Early Cretaceous (Berriasian) Angeac-Charente Lagerstätte (southwestern France): implications for continental faunal turnover at the J/K boundary. Geodiversitas, Museum National d’Histoire Naturelle Paris, In press. ffhal-03264773f
10. Apesteguía S, Gómez RO, Rougier GW (October 2014). "The youngest South American rhynchocephalian, a survivor of the K/Pg extinction". Proceedings. Biological Sciences. 281 (1792): 20140811. doi:10.1098/rspb.2014.0811. PMC 4150314. PMID 25143041.