Mesochelydia Explained

Mesochelydia (from Greek mesos "middle" and chelys "turtle") is a clade within Pantestudines, more inclusive than Perichelydia, but less than Testudinata. The clade is known from the Early Jurassic to the Present, and contains all Jurassic representatives of Testudinata aside from Australochelys.^[1] The ancestral condition for Mesochelydia is thought to be aquatic, as opposed to terrestrial for Testudinata.^[2] They are distinguished from more basal testudinatans by the presence of the following characters: strap like pectoral girdle, supramarginals absent, reduced posterior entoplastral process, eleven pairs of peripherals, elongate processus interfenestralis, paired basioccipital tubercles, fully formed cavum tympani and antrum postoticum, single vomer, confluent external nares, lacrimals and supratemporals absent.

Taxonomy

• Condorchelys Sterli, 2008 Cañadón Asfalto Formation, Toarcian, Argentina
• Eileanchelys Anquetin et al. 2009 Kilmaluag Formation, Bathonian, Scotland
• Heckerochelys Sukhanov, 2006^[3] Moskvoretskaya Formation, Bathonian, Russia
• Indochelys Datta et al., 2000^{[4] [5]} Kota Formation, Toarcian, India
• Kayentachelys Gaffney et al. 1987 Kayenta Formation, Sinemurian, United States
• Perichelydia Joyce, 2017 Middle Jurassic-Present, Worldwide

Additionally, an indeterminate basal non-perichelydian mesochelydian taxon is known from the Early Cretaceous Batylykh Formation in Russia.^[6]

Notes and References

1. Joyce. Walter G.. April 2017. A Review of the Fossil Record of Basal Mesozoic Turtles. Bulletin of the Peabody Museum of Natural History. en. 58. 1. 65–113. 10.3374/014.058.0105. 54982901. 0079-032X.
2. Sterli. Juliana. de la Fuente. Marcelo S.. Rougier. Guillermo W.. 2018-07-04. New remains of Condorchelys antiqua (Testudinata) from the Early-Middle Jurassic of Patagonia: anatomy, phylogeny, and paedomorphosis in the early evolution of turtles. Journal of Vertebrate Paleontology. en. 38. 4. (1)–(17). 10.1080/02724634.2018.1480112. 109556104. 0272-4634. 11336/99525. free.
3. V. B. Sukhanov. 2006. An archaic turtle, Heckerochelys romani gen. et sp. nov. from the Middle Jurassic of Moscow region, Russia. Fossil Turtle Research 1:112-118
4. Datta. P.M.. Manna. P.. Ghosh. S.C.. Das. D. P.. April 2000. The First Jurassic turtle from India. Palaeontology. 43. 1. 99–109. 10.1111/1475-4983.00120. 0031-0239. free.
5. Joyce. Walter G.. Bandyopadhyay. Saswati. 2020-02-11. A reevaluation of the basal turtle Indochelys spatulata from the Early–Middle Jurassic (Toarcian–Aalenian) of India, with descriptions of new material. PeerJ. 8. e8542. 10.7717/peerj.8542. 32095362. 7020818. 2167-8359 . free .
6. Skutschas. Pavel P.. Markova. Valentina D.. Kolchanov. Veniamin V.. Averianov. Alexander O.. Martin. Thomas. Schellhorn. Rico. Kolosov. Petr N.. Grigoriev. Dmitry V.. Vitenko. Dmitry D.. Obraztsova. Ekaterina M.. Danilov. Igor G.. February 2020. Basal turtle material from the Lower Cretaceous of Yakutia (Russia) filling the gap in the Asian record. Cretaceous Research. en. 106. 104186. 10.1016/j.cretres.2019.07.016. 202195840.