Cryptodira

Cryptodira Fossil range: Jurassic - Recent
Aldabra Giant Tortoise (Dipsochelys dussumieri)
Scientific classification
Kingdom: Animalia Phylum: Chordata Subphylum: Vertebrata Superclass: Tetrapoda Class: Sauropsida Subclass: Anapsida Order: Testudines Suborder: Cryptodira
Infraorders
Paracryptodira Eucryptodira and see text
Synonyms
Cryptodiramorpha Lee, 1995

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 it is along the body under the shell's margin. They also include in their species freshwater turtles, snapping turtles, tortoises, soft shell turtles, and sea turtles.

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

• Basal genera
  • Genus Kayentachelys (fossil; sometimes monotypic family Kayentachelyidae)
  • Genus Indochelys (fossil; sometimes monotypic family Indochelyidae)

Manchurochelys liaoxiensis was a paracryptodire.

• Infraorder Paracryptodira (fossil)
  • Basal and incertae sedis
    • Family Kallokibotiidae
    • Family Mongolochelyidae
    • Family Pleurosternidae
    • Family Solemydidae
  • Superfamily Baenoidea
    • Family Baenidae
    • Family Macrobaenidae
    • Family Neurankylidae

Meiolania platyceps was a primitive eucryptodire.

Kinixys belliana from the Testudinidae...

...and the Indian Flap-shelled Turtle (Lissemys punctata) from the Trionychidae are highly advanced eucryptodires.

• Infraorder Eucryptodira
  • Basal and incertae sedis
    • Family Eurysternidae (fossil)
    • Family Plesiochelyidae (fossil)
    • Family Xinjiangchelyidae (fossil)
  • Clade Centrocryptodira
    • "Sinemys" wuerhoensis (fossil)
    • Genus Chubutemys (fossil; Meiolaniidae?)
    • Family Meiolaniidae (horned turtles; fossil)
    • Genus Osteopygis (fossil)
    • Family Macrobaenidae (fossil; paraphyletic? May belong in Paracryptodira)
    • Family Sinemydidae (fossil; paraphyletic?)
    • Genus Judithemys (fossil)
    • Genus Hangaiemys ("Macrobaenidae"?)
    • Clade Polycryptodira
      • Family Chelydridae (snapping turtles)
      • Superfamily Chelonioidea (sea turtles)
        • Family Protostegidae (fossil)
        • Family Thalassemyidae (fossil)
        • Family Toxochelyidae (fossil)
        • Family Cheloniidae (green sea turtles and relatives)
        • Family Dermochelyidae (leatherback turtles)
      • Genus Planetochelys (fossil)
      • Superfamily Testudinoidea
        • Family Haichemydidae (fossil)
        • Family Lindholmemydidae (fossil)
        • Family Sinochelyidae (fossil)
        • Family Platysternidae (big-headed turtle)
        • Family Emydidae (pond, box and water turtles)
        • Family Geoemydidae (Asian river turtles, Asian leaf turtles, Asian box turtles and roofed turtles)
        • Family Testudinidae (tortoises)
      • Superfamily Trionychoidea
        • Family Adocidae (fossil)
        • Family Carettochelyidae (pignose turtles)
        • Family Dermatemydidae (river turtles)
        • Family Kinosternidae (mud turtles)
        • Family Trionychidae (softshell turtles)

Footnotes

References

• 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.

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