Opisthias Explained

Opisthias is a genus of sphenodont reptile. The type species, Opisthias rarus, is known from the Late Jurassic (Kimmeridgian-Tithonian) of western North America.^{[1] [2]}

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), present in stratigraphic zones 2 and 4–6.^[3] Other remains suggested to be closely related to Opisthias are also known from the Late Jurassic Alcobaça Formation of Portugal.^{[4] [5]} A undescribed crushed skull (DINO 16454) from the Morrison Formaiton has been attributed to this genus by some sources, though this has been strongly disputed by others.^[6]

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.^[7] A fragmentary dentary possibly attributable to Opisthias is also known from the Berriasian aged Angeac-Charente bonebed in France.^[8]

Diet

Opisthias has been interpreted as a generalist, with its tooth morphology indicating had an ability to process plant material.^[9]

See also

• Prehistoric reptile
• Paleobiota of the Morrison Formation

Notes and References

1. Book: 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 . 58–59 .
2. 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. 10.4202/app.00929.2021. free.
3. Book: Jurassic West: The Dinosaurs of the Morrison Formation and Their World . Foster J . 2007 . Indiana University Press . 327–329 . Appendix.
4. Web site: Herrera-Flores JA, Stubbs TL . 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 . July 2018 .
5. 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 . 10.5209/rev_JIGE.2010.v36.n2.7 . 1698-6180. free . 2010JIbG...36..193M .
6. 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 . en . 20 . 1 . 2093139 . 10.1080/14772019.2022.2093139 . 1477-2019. free . 2440/136608 . free .
7. Herrera-Flores J . 2020. Randall C . New insights on an enigmatic sphenodontian jaw from Dorset. Proceedings of the Dorset Natural History and Archaeological Society. 141. 41–43.
8. 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
9. Apesteguía S, Gómez RO, Rougier GW . The youngest South American rhynchocephalian, a survivor of the K/Pg extinction . Proceedings. Biological Sciences . 281 . 1792 . 20140811 . October 2014 . 25143041 . 4150314 . 10.1098/rspb.2014.0811 .