__NOTOC__ Paracryptodira is an extinct group of reptiles in the clade

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 T ...

(which contains modern

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

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 Mya. The J ...

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

of North America and Europe. Initially treated as a suborder

sister A sister is a woman or a girl who shares one or more parents 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 refer to ...

Cryptodira The Cryptodira ('' el, hidden neck'') are a suborder of Testudines that includes most living tortoises and turtles. Cryptodira differ from Pleurodira (side-necked turtles) in that they lower their necks and pull the heads straight back into t ...

,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''; plural 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 n ...

.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 mushr ...

-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 differe ...

. 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 __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 ...

, 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 In anatomy and osteology, a foramen (;Entry "foramen"
in

for the internal

carotid canal The carotid canal is a passageway in the temporal bone of the skull through which the internal carotid artery enters the middle cranial fossa from the neck. Structure The carotid canal is located within the middle cranial fossa, at the petrou ...

is located midway along the basisphenoid-pterygoid suture.

Subtaxa

Paracryptodira includes these taxa, after Joyce and Rollot, 2020. * ''

Dinochelys ''Dinochelys'' (from Greek ''deinos'' -terrible- and ''chelys'' -turtle) is an extinct genus of paracryptodiran turtle from the Late Jurassic Morrison Formation The Morrison Formation is a distinctive sequence of Late Jurassic, Upper Jura ...

'' * Family: †

** '' Calissounemys'' Var, France, Late Cretaceous (

Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campani ...

) ** ''

Compsemys ''Compsemys '' is an extinct genus of prehistoric turtles from the Late Cretaceous and Paleocene of North America and possibly Europe. The type species ''C. victa'', first described by Joseph Leidy from the Hell Creek Formation in Montana i ...

'' Late Cretaceous-Paleocene North America, Europe ** ''

Kallokibotion ''Kallokibotion'' is an extinct genus of stem-turtle from the Upper Cretaceous ( Maastrichtian, 86–66 million years ago), known from fossils found in Romania. One species is known, ''Kallokibotion bajazidi'', which was named by Franz Nopcsa ...

''? ** '' Peltochelys'' Sainte-Barbe Clays Formation, Belgium, Early Cretaceous (

Barremian The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 129.4 ± 1.5 Ma ( million years ago) and 121.4 ± 1.0 Ma). It is a subdivision of the Early Cretaceous Epoch (or Lower Cretaceous Series). It is pre ...

) ** '' Riodevemys'' Villar del Arzobispo Formation, Spain, Late Jurassic (Tithonian) ** ''

Selenemys ''Selenemys'' is an extinct genus of pleurosternid turtle from the Late Jurassic of Central West of Portugal. It is known from several specimens recovered from the Lusitanian Basin, dating to the upper Kimmeridgian age. It was one of the ea ...

'' Lourinhã Formation, Portugal, Late Jurassic (

Kimmeridgian In the geologic timescale, the Kimmeridgian is an age in the Late Jurassic Epoch and a stage in the Upper Jurassic Series. It spans the time between 157.3 ± 1.0 Ma and 152.1 ± 0.9 Ma (million years ago). The Kimmeridgian follows the Oxford ...

) ** ''

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 In the geological timescale, the Berriasian is an age/ stage of the Early/Lower Cretaceous. It is the oldest subdivision in the entire Cretaceous. It has been taken to span the time between 145.0 ± 4.0 Ma and 139.8 ± 3.0 Ma (million years a ...

) * †'' 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 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. St ...

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 ...

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