Cryptodira

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Cryptodira
Temporal range: Late Jurassic–Present
Aldabra giant tortoise (Aldabrachelys gigantea)
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Testudines
Suborder: Cryptodira
Cope, 1868[1]
Subgroups

See text

Synonyms[1][2]

Cryptoderes Duméril and Bibron, 1834
Cryptodera Lichtenstein, 1856
Cryptodira Cope, 1868
Cryptodiramorpha Lee, 1995
Pancryptodira Joyce, Parham, and Gauthier, 2004

Skull of a cryptodiran turtle from the family Emydidae
Dorsal view of skull and cervical vertebrae of a cryptodiran turtle from the family Emydidae. Not all cervical vertebrae are featured due to the dissection cut.

The Cryptodira (

sea turtles
.

Neck retraction

The Cryptodira are characterized by retraction of the head in the vertical plane, which permits for primarily vertical movements and restricted lateral movements outside of the shell.

ginglymoidy, and ultimately, their “hidden” neck retraction. Ginglymoidy refers to the double articulation where articulation between the sixth and seventh vertebrae and the seventh and eighth vertebrae allows for bending of the neck into an S shape. Formation of this S shape occurs in one plane that enables retraction into the shell.[5]

Cryptodiran neck retraction is also dependent on associated cervical musculature for its characteristic motions. A study that focused solely on the mechanism of neck retraction in

transverse processes (the lateral processes of a vertebra), forcing them to be developed in a more cranial direction. The iliocostalis system, used for lateral flexion and extension of the vertebral column, is commonly absent in all turtles. With the presence of a shell, these muscular movements are no longer possible. Epaxial musculature that functions in alternated forms of stepping and walking is minimized in turtles, due to their restricted stride lengths and heavily weighted shells.[citation needed
]

Systematics and evolution

Cryptodires

evolved from pleurodires during the early Jurassic period, originating from South America and Southeast Asia.[6] By the end of the Jurassic, cryptodires had almost completely replaced pleurodires in the lakes and rivers, while beginning to develop land-based species. Meanwhile, pleurodires became the dominant freshwater testudines in the Cretaceous to Eocene of Europe,[7] and produced a family of marine species, the Bothremydidae
.

The Cryptodira suborder has four living

Trionychoidea (soft-shell turtles and relatives). Chelydridae (snapping turtles) form a sister group to Kinosternoidea. The former three subfamilies (and Chelydridae) are classified in the clade Durocryptodira, while the latter is classified in the clade Trionychia. These two clades likely diverged in the middle of the Jurassic.[6][8]

Two circumscriptions of the Cryptodira are commonly found. One is used here; it includes a number of primitive

basal
groups, and the Centrocryptodira contain the prehistoric relatives of the living cryptodires, as well as the latter, which are collectively called Polycryptodira or Durocryptodira.

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. A recent study placed
Testudines, thus Cryptodira.[9]

As per the system used here, the Cryptodira can be classified as:[8][10]

Manchurochelys liaoxiensis was a member of Sinemydidae
.
Testudinidae
The Indian flapshell turtle (Lissemys punctata) from the Trionychidae is a highly advanced eucryptodire.

Distribution

  • Trionychidae (softshell turtles) are found from North America, Africa, South and East Asia to New Guinea.
  • Kinosternidae (mud and musk turtles) are found from eastern North America to the Amazon drainage of South America.
  • Dermatemydidae (Mesoamerican river turtles) are found in the Caribbean-Gulf drainage of Mesoamerica.
  • Emydidae (cooters, sliders, American box turtles, and Allies) are found from Europe to Ural Mountains and North America southward to Eastern Brazil.

References

  1. ^ a b Rhodin 2011, p. 000.171
  2. ^ Rhodin 2008, p. 000.3
  3. PMID 28206991
    .
  4. ^
    OCLC 144570900.{{cite book}}: CS1 maint: others (link
    )
  5. ^ "ginglymoidy - oi". Archived from the original on 2020-01-31. Retrieved 2018-05-05. {{cite journal}}: Cite journal requires |journal= (help)
  6. ^
    PMID 28501611
    .
  7. S2CID 15652309
    .
  8. ^
    ISSN 1664-2384
    .
  9. S2CID 134736808
    .
  10. S2CID 85295987
    .

Further reading
Wikispecies has information related to Cryptodira.
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