__NOTOC__ Paracryptodira is an extinct group of reptiles in the

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, ...

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 ...

(which contains modern turtles and their extinct relatives), known from the Jurassic to

Paleogene The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period, geologic period and system that spans 43 million years from the end of the Cretaceous Period million yea ...

of North America and Europe. Initially treated as a suborder sister to Cryptodira,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.Joyce (2007) They are now often regarded as late-diverging

stem Stem or STEM may refer to: Plant structures * Plant stem, a plant's aboveground axis, made of vascular tissue, off which leaves and flowers hang * Stipe (botany), a stalk to support some other structure * Stipe (mycology), the stem of a mushro ...

-turtles, lying outside the clade formed by Cryptodira and Pleurodira. The paracryptodires are said to have phylogenic relationships, noted as primary subclades, within the Baenidae and Pleurosternidae. Within each subclade, lies many biodiverse turtles that are continuously being investigated and added to the fossil record. Paracryptodires are divided into three main groups, Compsemydidae, known from the Late Jurassic to Paleocene of North America and Europe, Pleurosternidae, known from the Late Jurassic to Early Cretaceous of North America and Europe, and Baenidae, 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 for the internal carotid canal is located midway along the basisphenoid-pterygoid suture.

Subtaxa

Paracryptodira includes these taxa, after Joyce and Rollot, 2020. * '' Dinochelys'' * Family: † Compsemydidae ** '' Calissounemys'' Var, France, Late Cretaceous ( Campanian) ** '' Compsemys'' Late Cretaceous-Paleocene North America, Europe ** '' Kallokibotion''? ** '' Peltochelys''

Sainte-Barbe Clays Formation The Sainte-Barbe Clays Formation is a geological formation in Belgium. It is found in localised areas of the northern margin of the Mons Basin, alongside the equivalently aged Hautrage and Baudour Clay Formations. It is Upper Barremian-Lower Aptian ...

, Belgium, Early Cretaceous ( Barremian) ** '' Riodevemys'' Villar del Arzobispo Formation, Spain, Late Jurassic (Tithonian) ** '' Selenemys'' Lourinhã Formation, Portugal, Late Jurassic ( Kimmeridgian) ** ''

Tongemys ''Tongemys'' is an extinct genus of compsemydid turtle that lived in England during the Berriasian In the geological timescale, the Berriasian is an age/stage of the Early/Lower Cretaceous. It is the oldest subdivision in the entire Creta ...

'' Purbeck Group, England, Early Cretaceous ( Berriasian) * †'' Uluops'' * †

Baenoidea __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 si ...

** Family: † Baenidae ** Family: † Pleurosternidae *** Family:

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 ...

? Dubious species: * Species: †'' Polythorax missuriensis'' * Species: † ''Desmemys'' ''bertelmanni'' * Species: †''

Glyptops caelatus ''Glyptops'' (Greek for "grooved face") 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 ...

'' * Species: † ''Glyptops'' ''pervicax'' * Species: †'' Probaena sculpta'' The oldest possible record of paracryptodires is from the Forest Marble Formation of England, dating to the Bathonian stage of the

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 ...

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