Editing Turtle (section)

=== Differences between the two suborders ===

{{Multiple image
|header = Neck retraction
|total_width = 410
|perrow = 2
|image1 = T.h. hermanni con speroni 5.JPG
|caption1 = [[Cryptodira]] retract their necks backward.
|alt1 = Photograph of a cryptodiran with its head pulled back straight into its shell
|image2 = Pelomedusa subrufa (cropped).JPG
|caption2 = [[Pleurodira]] retract their necks sideways.
|alt2 = Photograph of a pleurodiran with its head and neck folded toward the side
|image3 = Turtle neck retraction.svg
|caption3 = The different mechanisms of neck retraction in the two suborders of turtles
|alt3=Diagrams of the top-down bending of the neck of cryptodirans, and the left-right bending of the neck in pleurodirans
}}

Turtles are divided into two living suborders: Cryptodira and Pleurodira.<ref name="Joyce 2021">{{Cite journal |last1=Joyce |first1=Walter G. |last2=Anquetin |first2=Jérémy |last3=Cadena |first3=Edwin-Alberto |last4=Claude |first4=Julien |last5=Danilov |first5=Igor G. |last6=Evers |first6=Serjoscha W. |last7=Ferreira |first7=Gabriel S. |last8=Gentry |first8=Andrew D. |last9=Georgalis |first9=Georgios L. |last10=Lyson |first10=Tyler R. |last11=Pérez-García |first11=Adán |date=February 9, 2021 |title=A Nomenclature for Fossil and Living Turtles Using Phylogenetically Defined Clade Names |journal=[[Swiss Journal of Palaeontology]] |volume=140 |issue=1 |page=5 |doi=10.1186/s13358-020-00211-x |issn=1664-2384 |display-authors=3 |doi-access=free |bibcode=2021SwJP..140....5J |hdl=11336/155192 |hdl-access=free }}</ref> The two groups differ in the way the neck is retracted for protection. Pleurodirans retract their neck to the side and in front of the shoulder girdles, whereas cryptodirans retract their neck backward into their shell. These motions are enabled by the morphology and arrangement of neck vertebrae.<ref name="Werneburg 2015">{{cite journal |last1=Werneburg |first1=Ingmar |last2=Wilson  |first2=Laura A. B. |last3=Parr |first3=William C. H. |last4=Joyce |first4=Walter G. |date=March 1, 2015 |title=Evolution of Neck Vertebral Shape and Neck Retraction at the Transition to Modern Turtles: an Integrated Geometric Morphometric Approach |journal=Systematic Biology |volume=64 |issue=2 |pages=187–204 |doi=10.1093/sysbio/syu072 |pmid=25305281 |issn=1063-5157 |doi-access=free|hdl=1959.4/unsworks_54973 |hdl-access=free }}</ref><ref name="Herrel 2008">{{cite book |last1=Herrel |first1=Anthony |last2=Van Damme |first2=Johan |last3=Aerts |first3=Peter |chapter=Cervical Anatomy and Function in Turtles |editor-last=Wyneken |editor-first=Jeanette |editor-last2=Bels |editor-first2=V. L. |editor-last3=Godfrey |editor-first3=Matthew H. |title=Biology of Turtles |year=2008 |publisher=CRC Press |isbn=978-0-8493-3339-2 |oclc=144570900 |pages=163–186}}</ref> Sea turtles (which belong to Cryptodira) have mostly lost the ability to retract their heads.{{sfn|Orenstein|2012|p=110}}

The adductor muscles in the lower jaw create a pulley-like system in both subgroups. However, the bones that the muscles articulate with differ. In Pleurodira, the pulley is formed with the [[pterygoid bone]]s of the [[palate]], but in Cryptodira the pulley is formed with the otic capsule. Both systems help to vertically redirect the [[Anatomical terms of motion#Abduction and adduction|adductor]] muscles and maintain a powerful bite.<ref name="Ferreira Lautenschlager Evers Pfaff 2020">{{cite journal |last1=Ferreira |first1=Gabriel S. |last2=Lautenschlager |first2=Stephan |last3=Evers |first3=Serjoscha W. |last4=Pfaff |first4=Cathrin |last5=Kriwet |first5=Jürgen |last6=Raselli |first6=Irena |last7=Werneburg |first7=Ingmar |title=Feeding Biomechanics Suggests Progressive Correlation of Skull Architecture and Neck Evolution in Turtles |journal=Scientific Reports |volume=10 |issue=1 |date=March 26, 2020 |issn=2045-2322 |doi=10.1038/s41598-020-62179-5 |pmid=32218478 |pmc=7099039 |bibcode=2020NatSR..10.5505F |display-authors=3 |at=article 5505 |doi-access=free }}</ref>

A further difference between the suborders is the attachment of the pelvis. In Cryptodira, the pelvis is free, linked to the shell only by ligaments. In Pleurodira, the pelvis is [[Suture (anatomy)|sutured]], joined with bony connections, to the carapace and to the plastron, creating a pair of large columns of bone at the back end of the turtle, linking the two parts of the shell.<ref name="Wise Stayton 2017">{{cite journal |last1=Wise |first1=Taylor B. |last2=Stayton |first2=C. Tristan |title=Side-necked Versus Hidden-necked: Comparison of Shell Morphology Between Pleurodiran and Cryptodiran Turtles |journal=Herpetologica |date=2017 |volume=73 |issue=1 |pages=18–29 |doi=10.1655/HERPETOLOGICA-D-15-00038 |jstor=26534349 |s2cid=90226667 }}</ref>