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 neck and pull the head straight back into the shell, instead of folding the neck sideways along the body under the shell's margin.
Systematics and evolution
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 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.[1]
There are two commonly-found circumscriptions of the Cryptodira. 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, which contains the prehistoric relatives of the living cryptodires as well as the latter which are collectively called Polycryptodira.[1]
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.[1]
As per the system used here, the Cryptodira can be classified as follows:[1]
SUBORDER CRYPTODIRA
Footnotes
- ^ a b c d See references in Haaramo (2008)
References
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