__NOTOC__ Paracryptodira is an extinct group of reptiles in the

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 ...

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 ...

(which contains modern

turtle 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 ...

s and their extinct relatives), known from the

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

Paleogene The Paleogene Period ( ; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the fir ...

of North America and Europe. Initially treated as a suborder

sister A sister is a woman or a girl who shares parents or a parent with another individual; a female sibling. The male counterpart is a brother. Although the term typically refers to a familial relationship, it is sometimes used endearingly to ref ...

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 ...

,Gaffney (1975) they were then thought to be a very primitive lineage inside the Cryptodira according to the most common use of the latter

taxon In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

.Joyce (2007) They are now often regarded as late-diverging

stem Stem or STEM most commonly refers to: * Plant stem, a structural axis of a vascular plant * Stem group * Science, technology, engineering, and mathematics Stem or STEM can also refer to: Language and writing * Word stem, part of a word respon ...

-turtles, lying outside the clade formed by Cryptodira and

Pleurodira The Pleurodira are one of the two living suborders of turtles, the other being the Cryptodira. The division between these two suborders represents a very deep evolutionary divide between two very different types of turtles. The physical differ ...

. Paracryptodires are divided into three main groups,

Compsemydidae Compsemydidae is an extinct family of Testudinata, turtles, likely belonging to the clade Paracryptodira. The earliest undisputed member is ''Tongemys'' from the Berriasian age of the Early Cretaceous; two Late Jurassic genera (''Riodevemys'' and ...

, known from the Late Jurassic to Paleocene of North America and Europe,

Pleurosternidae Pleurosternidae is an extinct family of freshwater turtles belonging to Paracryptodira. They are definitively known from the Late Jurassic to Early Cretaceous (Albian) of Western Europe and North America. Genera Valid taxa *'' Dinochelys'' M ...

, known from the Late Jurassic to Early Cretaceous of North America and Europe, and

Baenidae Baenidae is an extinct family of paracryptodiran turtles known from the Early Cretaceous to Eocene of North America. While during the Early Cretaceous they are found across North America, during the Late Cretaceous they are only found in Laramidi ...

, known from the Early Cretaceous to Eocene of North America. The latter two groups are more closely related to each other than to ''Compsemys'', forming the clade Baenoidea.

Characteristics

Paracryptodires have reduced prefrontal exposure on the dorsal surface of their skulls, reduced fenestrae perilymphaticae, and secondarily reduced supraoccipital crests. In the skull, the posterior

foramen In anatomy and osteology, a foramen (; : foramina, or foramens ; ) is an opening or enclosed gap within the dense connective tissue (bones and deep fasciae) of extant and extinct amniote animals, typically to allow passage of nerves, artery, ...

for the internal

carotid canal The carotid canal is a passage in the petrous part of the temporal bone of the skull through which the internal carotid artery and its internal carotid (nervous) plexus pass from the neck into (the middle cranial fossa of) the cranial cavity. ...

is located midway along the basisphenoid-pterygoid suture.

Subtaxa

Paracryptodira includes these taxa, after Rollot ''et al.'' (2022): *

? *

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 ...

? * '' Dinochelys'' * ''

Dorsetochelys ''Dorsetochelys'' is an extinct genus of turtle from the Early Cretaceous of southern England and northwestern Germany. Taxonomy The type species, ''Dorsetochelys delairi'', was described on the basis of DORCM G.23, a complete skull from the Ear ...

'' * ''

Glyptops ''Glyptops'' is an extinct genus of pleurosternid freshwater turtle known from the Late Jurassic of North America. Taxonomy The type species, ''Glyptops plicatulus'', was first described as ''Compsemys plicatulus'' by Edward Drinker Cope on the ...

'' * ''

Uluops ''Uluops'' is an extinct genus of paracryptodire turtle from the Late Jurassic (Tithonian) of North America. The type and only species is ''Uluops uluops'', which is known from a single skull from the Morrison Formation The Morrison Formation ...

'' * Baenoidea **

Dubious species: * '' Polythorax missuriensis'' * '' Desmemys bertelmanni'' * ''

Glyptops caelatus ''Glyptops'' is an extinct genus of pleurosternid freshwater turtle known from the Late Jurassic of North America. Taxonomy The type species, ''Glyptops plicatulus'', was first described as ''Compsemys plicatulus'' by Edward Drinker Cope on the ...

'' * ''

Glyptops pervicax ''Glyptops'' is an extinct genus of pleurosternid freshwater turtle known from the Late Jurassic of North America. Taxonomy The type species, ''Glyptops plicatulus'', was first described as ''Compsemys plicatulus'' by Edward Drinker Cope on the ...

'' * '' Probaena sculpta'' The oldest possible record of paracryptodires is from the

Forest Marble Formation The Forest Marble is a geological formation in England. Part of the Great Oolite Group, it dates to the late Bathonian stage of the Middle Jurassic.Weishampel, David B; et al. (2004). "Dinosaur distribution (Middle Jurassic, Europe)." In: Weisha ...

of England, dating to the

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 ...

stage of 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 ...

References

Sources

* (1975): A phylogeny and classification of higher categories of turtles. ''Bulletin of the American Museum of Natural History'' 155(5): 387–436
PDF fulltext
* (2007): Phylogenetic relationships of Mesozoic turtles. ''Bulletin of the Peabody Museum of Natural History'' 48(1): 3–102. DOI:10.3374/0079-032X(2007)48 :PROMT.0.CO;2HTML abstract

External links

Testudines
{{Taxonbar, from=Q2633585 Jurassic first appearances Cretaceous turtles Eocene genus extinctions Taxa named by Eugene S. Gaffney