Temporal range: Early Jurassic—Present, 190–0Ma 
|Aldabra giant tortoise (Aldabrachelys gigantea)|
Cryptoderes Duméril and Bibron, 1834
Cryptodira is the taxonomic suborder of Testudines that includes most living tortoises and turtles. Cryptodira differ from Pleurodira (side-neck turtles) in that they lower their necks and pull the heads straight back into the shells; instead of folding their necks sideways along the body under the shells' margins. They include among their species freshwater turtles, snapping turtles, tortoises, soft shell turtles, and sea turtles.
Systematics and evolution
The earliest known cryptodire fossils belong to the species Kayentachelys aprix, from the early Jurassic period of Arizona (around 190 million years ago). Cryptodires evolved primarily through the Jurassic period, and by the end of the Jurassic had almost completely replaced Pleurodires in the lakes and rivers, while beginning to develop land-based species.
Cryptodira has three living superfamilies, the Chelonioidea (sea turtles), Testudinoidea (tortoises and pond turtles) and Trionychoidea (softshell turtles and relatives). The Kinosternoidea are now recognized as a paraphyletic assemblage of mostly primitive Trionychoidea; they do not form a natural group.
Two circumscriptions of the Cryptodira are commonly found. One is used here; it includes a number of primitive extinct lineages known only from fossils, as well as the Eucryptodira. These are, in turn, made up from some very basal groups, and the Centrocryptodira contains the prehistoric relatives of the living cryptodires, as well as the latter, which are collectively called Polycryptodira.
The alternate concept restricts the use of the term "Cryptodira" to the crown clade (i.e. Polycryptodira). The Cryptodira as understood here are called Cryptodiramorpha in this view. Under this approach, the pleurodires and cryptodires are not sister taxa.
As per the system used here, the Cryptodira can be classified as:
- Basal genera
- †Infraorder Paracryptodira
- Infraorder Eucryptodira
- Basal and incertae sedis
- Clade †Centrocryptodira
- Clade Polycryptodira
- Family Chelydridae (snapping turtles)
- Superfamily Chelonioidea (sea turtles)
- Genus †Planetochelys
- Superfamily Kinosternoidea
- Superfamily Testudinoidea
- Superfamily Trionychia
- Baur, George (1890): On the Classification of the Testudinata. Am. Nat. 24(282): 530-536. doi:10.1086/275138 First page image
- Haaramo, Mikko (2008): Mikko's Phylogeny Archive - Cryptodira. Version of 2008-MAR-11. Retrieved 2008-MAY-07.
- Rhodin, Anders G.J.; van Dijk, Peter Paul; Inverson, John B.; Shaffer, H. Bradley; Roger, Bour (2011-12-31). "Turtles of the world, 2011 update: Annotated checklist of taxonomy, synonymy, distribution and conservation status". Chelonian Research Monographs 5. Archived from the original on 2012-01-22.
- Rhodin, Anders G.J.; van Dijk, Peter Paul; Parham, James F. (2008-12-08). "Turtles of the world, 2008 checklist". Chelonian Research Monographs 5. Archived from the original on 2011-09-05.
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