Mesochelydia (from

Greek Greek may refer to: Greece 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 ...

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

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

within

Pantestudines Pantestudines or Pan-Testudines is the group of all 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 extinct relatives (also ...

, more inclusive than

Perichelydia Perichelydia (from Greek ''peri'' "near" and ''chelys'' "turtle") is a clade within Pantestudines (turtles and their extinct relatives) known from the Middle Jurassic to Holocene. Alongside crown group Testudines, it also contains Helochelydrid ...

, 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 it was first coined as the group containing turtles by Jacob The ...

. The clade is known from the Early Jurassic to the Present, and contains all Jurassic representatives of Testudinata aside from ''

Australochelys ''Australochelys'' is an extinct genus of rhaptochelydian turtle. It is known from one species, ''A. africanus'', that came from the Elliot Formation of South Africa. The holotype of ''Australochelys'' consists of only a skull and a fragment of ...

.'' 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 of t ...

, supramarginals absent, reduced posterior entoplastral process, eleven pairs of peripherals, elongate processus interfenestralis, paired basioccipital tubercles, fully formed

cavum tympani The tympanic cavity is a small cavity surrounding the bones of the middle ear. Within it sit the ossicles, three small bones that transmit vibrations used in the detection of sound. Structure On its lateral surface, it abuts the external auditory ...

and antrum postoticum, single

vomer The vomer (; lat, vomer, lit=ploughshare) 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 maxill ...

, confluent external nares,

lacrimals The lacrimal bone is a small and fragile bone of the facial skeleton; it is roughly the size of the little fingernail. It is situated at the front part of the medial wall of the Orbit (anatomy), orbit. It has two surfaces and four borders. Several ...

and

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

s absent.

Taxonomy

* ''

Condorchelys ''Condorchelys'' was a genus of stem turtle from Early Jurassic Cañadon Asfalto Formation of Argentina. Only one species is described, ''Condorchelys antiqua''.Sterli, 2008 References Bibliography

* Prehistoric turtle genera Baj ...

'' Sterli, 2008

Cañadón Asfalto Formation The Cañadón Asfalto Formation is a Lower Jurassic to Late Jurassic geologic formation, from the Jurassic period of the Mesozoic Era. Its age is controversial, uranium-lead dating of the volcanic tuff beds having given various different ages. A ...

Middle Jurassic The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from about 174.1 to 163.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare, but geological formations co ...

, Argentina * ''

Eileanchelys ''Eileanchelys'' is an extinct genus of primitive turtle from the Middle Jurassic (Bathonian) period some 164 million years ago of Britain. Only one species is recorded, ''Eileanchelys waldmani''. It is the best-represented turtle from the Midd ...

'' Anquetin et al. 2009

Kilmaluag Formation The Kilmaluag Formation is a Middle Jurassic geologic formation in Scotland. It was formerly known as the Ostracod Limestone for the abundance of fossil freshwater ostracods within it. The Kilmaluag Formation is very fossiliferous, with ostracods ...

Bathonian In the geologic timescale the Bathonian is an age and stage of the Middle Jurassic. It lasted from approximately 168.3 Ma to around 166.1 Ma (million years ago). The Bathonian Age succeeds the Bajocian Age and precedes the Callovian Age. Strat ...

, Scotland * '' Heckerochelys'' Sukhanov, 2006

Moskvoretskaya Formation The Moskvoretskaya Formation is a Middle Jurassic (Bathonian stage) geologic formation in the European part of Russia. It consists of continental claystones, siltstones and sandstones deposited in karstified segments of underlying Middle Carboni ...

, Bathonian, Russia * '' Indochelys'' Datta et al, 2000

Kota Formation The Kota Formation is a geological formation in India. The precise age of Kota Formation are uncertain, but it dates from the Early to Middle Jurassic, and is split into a Lower Member and Upper Member.Prasad GVR, and Manhas BK. 2007A new docodon ...

Toarcian The Toarcian is, in the ICS' geologic timescale, an age and stage in the Early or Lower Jurassic. It spans the time between 182.7 Ma (million years ago) and 174.1 Ma. It follows the Pliensbachian and is followed by the Aalenian. The Toarcian ...

, India * ''

Kayentachelys ''Kayentachelys'' ("Kayenta turtle") is an extinct genus of turtle known only from the "silty facies" of the Lower Jurassic Kayenta Formation in northeastern Arizona on the lands of the Navajo Nation. History of discovery and significance The e ...

'' 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 province of the United States, including northern Arizona, northwest Colorado, Nevada, and Utah. Traditionally has been suggested ...

Sinemurian In the geologic timescale, the Sinemurian is an age and stage in the Early or Lower Jurassic Epoch or Series. It spans the time between 199.3 ± 2 Ma and 190.8 ± 1.5 Ma (million years ago). The Sinemurian is preceded by the Hettangian and is ...

, United States *

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

Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pro ...

Batylykh Formation The Batylykh Formation is a geological formation in Yakutia, Russia. It is of an uncertain Early Cretaceous age, probably dating between the Berriasian and the Barremian. It is the oldest unit of the thick Sangar Series within the Vilyuy syne ...

in Russia.

References

{{Taxonbar, from=Q68334453 Testudinata