Perichelydia (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 ...

''peri'' "near" 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 ...

(turtles and their extinct relatives) known from the

Middle Jurassic The Middle Jurassic is the second Epoch (geology), epoch of the Jurassic Period (geology), Period. It lasted from about 174.1 to 161.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relativel ...

Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...

. Alongside

crown group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor ...

Testudines Turtles are reptiles of the order (biology), order Testudines, characterized by a special turtle shell, shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Crypt ...

, it also contains

Helochelydridae The Helochelydridae are an extinct family of stem-turtles known from fossils found in North America and Europe spanning the Early to Late Cretaceous. Description The skull, shell and osteoderms of helochelydrids are covered in small, cylindric ...

, which is known from the Cretaceous of Europe and North America,

Sichuanchelyidae Sichuanchelyidae is a family of extinct turtles in the clade Testudinata. It includes all perichelydians that are more closely related to '' Sichuanchelys'' than '' Meiolania'', '' Helochelydra'', or any extant turtles. Systematics The family S ...

from the

Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...

of Asia and Europe, Meiolaniformes, which is known from the Cretaceous to Holocene of South America, Australia and Oceania, and '' Spoochelys'', known from the Mid-Cretaceous Griman Creek Formation of Australia. '' Kallokibotion'' from the Late Cretaceous of Europe is also considered part of this group. Several other groups, including the proposed clade

Angolachelonia Angolachelonia is a clade of extinct turtles from the Late Jurassic to Paleogene of Eurasia. The group is defined as all taxa derived from the ancestor of the type genus ''Angolachelys'' and ''Solnhofia'', a definition that could potentially enco ...

(containing

Thalassochelydia Thalassochelydia is a clade of extinct marine turtles from the Late Jurassic and earliest Cretaceous of Europe and South America. The group is defined as including '' Eurysternum'', ''Plesiochelys'' and '' Thalassemys'' to the exclusion of '' Pel ...

and Sandownidae),

Paracryptodira __NOTOC__ Paracryptodira is an extinct group of reptiles in the clade Testudinata (which contains modern turtles and their extinct relatives), known from the Jurassic to Paleogene of North America and Europe. Initially treated as a suborder siste ...

Macrobaenidae Macrobaenidae is an extinct family of turtles, known from the Early Cretaceous to Paleogene of Laurasia. Their relationships to other turtles and whether they form a monophlyletic group are controversial. They are typically interpreted as stem o ...

, Sinemydidae and

Xinjiangchelyidae Xinjiangchelyidae is an extinct family of turtles known from the Lower Jurassic to the Middle Cretaceous of Asia and western Europe. They have generally been interpreted as either being basal Cryptodira, cryptodires or placed outside of crown Tes ...

, which are sometimes considered members of

Cryptodira The Cryptodira (') are a suborder of Testudines that includes most living tortoises and turtles. Cryptodira is commonly called the "Hidden-Neck Turtles" or the "Inside-Neck Turtles". Cryptodira differ from Pleurodira (side-necked turtles) in ...

, have also been found outside crown Testudines in several analyses. These groups are usually considered to be closer to the crown group than the other members of Perichelydia. The clade Perichelydia was created by W. G. Joyce in 2017. They are distinguished from other

mesochelydia 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 Jurassi ...

ns by two characters: the presence of ''processus trochlearis oticum'', and a closed ''interpterygoid vacuity''. Cladogram after Tong et al. 2022:

References

{{Taxonbar, from=Q64043742 Testudinata