Mesochelydia (from

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

''mesos'' "middle" and ''chelys'' "turtle") is a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

within

Pantestudines Pantestudines or Pan-Testudines is the proposed group of all Reptile, reptiles more closely related to turtles than to any other living animal. It includes both modern turtles (crown group turtles, also known as Testudines) and all of their extin ...

, more inclusive than Perichelydia, but less than

Testudinata Testudinata is the group of all tetrapods with a true turtle shell. It includes both modern turtles (Testudines) and many of their extinct, shelled relatives (stem-turtles), though excluding ''Odontochelys'' and ''Eorhynchochelys,'' which are pla ...

. The clade is known from the Early Jurassic to the Present, and contains all Jurassic representatives of Testudinata aside from '' Australochelys.'' The ancestral condition for Mesochelydia is thought to be aquatic, as opposed to terrestrial for Testudinata. They are distinguished from more basal testudinatans by the presence of the following characters: strap like

pectoral girdle The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans, it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists o ...

, 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 The vomer (; ) is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxillary bones. The vomer forms ...

, confluent external nares, lacrimals and

supratemporal The supratemporal bone is a paired Skull, cranial bone present in many Tetrapod, tetrapods and Tetrapodomorpha, tetrapodomorph fish. It is part of the temporal region (the portion of the skull roof behind the eyes), usually lying medial (inwards) re ...

s absent.

Taxonomy

* '' Condorchelys'' Sterli, 2008 Cañadón Asfalto Formation,

Toarcian The Toarcian is, in the International Commission on Stratigraphy, ICS' geologic timescale, an age (geology), age and stage (stratigraphy), stage in the Early Jurassic, Early or Lower Jurassic. It spans the time between 184.2 Megaannum, Ma (million ...

, Argentina * '' Eileanchelys'' Anquetin et al. 2009 Kilmaluag Formation,

Bathonian In the geologic timescale the Bathonian is an age (geology), age and stage (stratigraphy), stage of the Middle Jurassic. It lasted from approximately 168.2 ±1.2 annum, Ma to around 165.3 ±1.1 Ma (million years ago). The Bathonian Age succeeds ...

, Scotland * '' Heckerochelys'' Sukhanov, 2006 Moskvoretskaya Formation, Bathonian, Russia * '' Indochelys'' Datta et al., 2000 Kota Formation,

, India * '' Kayentachelys'' Gaffney et al. 1987

Kayenta Formation The Kayenta Formation is a geological formation in the Glen Canyon Group that is spread across the Colorado Plateau area of the United States, including northern Arizona, northwest Colorado, Nevada, and Utah. Originally suggested as being Sinemur ...

Sinemurian In the geologic timescale, the Sinemurian is an age (geology), age and stage (stratigraphy), stage in the Early Jurassic, Early or Lower Jurassic epoch (geology), Epoch or series (stratigraphy), Series. It spans the time between 199.5 ±0.3 annu ...

, United States * Perichelydia Joyce, 2017 Middle Jurassic-Present, Worldwide Additionally, an indeterminate basal non-perichelydian mesochelydian taxon is known from the

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

Batylykh Formation in Russia.

References

{{Taxonbar, from=Q68334453 Testudinata