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A new xinjiangchelyid turtle from the Middle Jurassic of Xinjiang, China and the evolution of the basipterygoid process in Mesozoic turtles.

Rabi M, Zhou CF, Wings O, Ge S, Joyce WG - BMC Evol. Biol. (2013)

Bottom Line: However, the analysis supports the unorthodox, though tentative placement of xinjiangchelyids and sinemydids outside of crown-group Testudines.A particularly interesting new observation is that the skull of this xinjiangchelyid retains such primitive features as a reduced interpterygoid vacuity and basipterygoid processes.The homology of basipterygoid processes is confidently demonstrated based on a comprehensive review of the basicranial anatomy of Mesozoic turtles and a new nomenclatural system is introduced for the carotid canal system of turtles.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institut für Geowissenschaften, University of Tübingen, Hölderlinstraße 12, 72074, Tübingen, Germany. iszkenderun@gmail.com.

ABSTRACT

Background: Most turtles from the Middle and Late Jurassic of Asia are referred to the newly defined clade Xinjiangchelyidae, a group of mostly shell-based, generalized, small to mid-sized aquatic froms that are widely considered to represent the stem lineage of Cryptodira. Xinjiangchelyids provide us with great insights into the plesiomorphic anatomy of crown-cryptodires, the most diverse group of living turtles, and they are particularly relevant for understanding the origin and early divergence of the primary clades of extant turtles.

Results: Exceptionally complete new xinjiangchelyid material from the ?Qigu Formation of the Turpan Basin (Xinjiang Autonomous Province, China) provides new insights into the anatomy of this group and is assigned to Xinjiangchelys wusu n. sp. A phylogenetic analysis places Xinjiangchelys wusu n. sp. in a monophyletic polytomy with other xinjiangchelyids, including Xinjiangchelys junggarensis, X. radiplicatoides, X. levensis and X. latiens. However, the analysis supports the unorthodox, though tentative placement of xinjiangchelyids and sinemydids outside of crown-group Testudines. A particularly interesting new observation is that the skull of this xinjiangchelyid retains such primitive features as a reduced interpterygoid vacuity and basipterygoid processes.

Conclusions: The homology of basipterygoid processes is confidently demonstrated based on a comprehensive review of the basicranial anatomy of Mesozoic turtles and a new nomenclatural system is introduced for the carotid canal system of turtles. The loss of the basipterygoid process and the bony enclosure of the carotid circulation system occurred a number of times independently during turtle evolution suggesting that the reinforcement of the basicranial region was essential for developing a rigid skull, thus paralleling the evolution of other amniote groups with massive skulls.

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Carapaces of Xinjiangchelys wusu, Middle Jurassic, ?Qigu Formation, “Turtle Cliff”, Shanshan area, Turpan Basin, Xinjiang Autonomous Province, China. A, PMOL-SGP A0100-1 (holotype), photograph and line drawing; B, PMOL-SGP A0100-2, photograph and line drawing. Abbreviations: CE: cervical scute, co: costal, ne: neural, nu: nuchal, per: peripheral, PL: pleural, VE: vertebral, py: pygal, sp: suprapygal.
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Figure 6: Carapaces of Xinjiangchelys wusu, Middle Jurassic, ?Qigu Formation, “Turtle Cliff”, Shanshan area, Turpan Basin, Xinjiang Autonomous Province, China. A, PMOL-SGP A0100-1 (holotype), photograph and line drawing; B, PMOL-SGP A0100-2, photograph and line drawing. Abbreviations: CE: cervical scute, co: costal, ne: neural, nu: nuchal, per: peripheral, PL: pleural, VE: vertebral, py: pygal, sp: suprapygal.

Mentions: (Figure 2, Figures 4, 5, 6, 7, and 8)urn:lsid:zoobank.org:pub:2BCCC095-7622-4 F27-8 F80-6199F24690B5


A new xinjiangchelyid turtle from the Middle Jurassic of Xinjiang, China and the evolution of the basipterygoid process in Mesozoic turtles.

Rabi M, Zhou CF, Wings O, Ge S, Joyce WG - BMC Evol. Biol. (2013)

Carapaces of Xinjiangchelys wusu, Middle Jurassic, ?Qigu Formation, “Turtle Cliff”, Shanshan area, Turpan Basin, Xinjiang Autonomous Province, China. A, PMOL-SGP A0100-1 (holotype), photograph and line drawing; B, PMOL-SGP A0100-2, photograph and line drawing. Abbreviations: CE: cervical scute, co: costal, ne: neural, nu: nuchal, per: peripheral, PL: pleural, VE: vertebral, py: pygal, sp: suprapygal.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3852240&req=5

Figure 6: Carapaces of Xinjiangchelys wusu, Middle Jurassic, ?Qigu Formation, “Turtle Cliff”, Shanshan area, Turpan Basin, Xinjiang Autonomous Province, China. A, PMOL-SGP A0100-1 (holotype), photograph and line drawing; B, PMOL-SGP A0100-2, photograph and line drawing. Abbreviations: CE: cervical scute, co: costal, ne: neural, nu: nuchal, per: peripheral, PL: pleural, VE: vertebral, py: pygal, sp: suprapygal.
Mentions: (Figure 2, Figures 4, 5, 6, 7, and 8)urn:lsid:zoobank.org:pub:2BCCC095-7622-4 F27-8 F80-6199F24690B5

Bottom Line: However, the analysis supports the unorthodox, though tentative placement of xinjiangchelyids and sinemydids outside of crown-group Testudines.A particularly interesting new observation is that the skull of this xinjiangchelyid retains such primitive features as a reduced interpterygoid vacuity and basipterygoid processes.The homology of basipterygoid processes is confidently demonstrated based on a comprehensive review of the basicranial anatomy of Mesozoic turtles and a new nomenclatural system is introduced for the carotid canal system of turtles.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institut für Geowissenschaften, University of Tübingen, Hölderlinstraße 12, 72074, Tübingen, Germany. iszkenderun@gmail.com.

ABSTRACT

Background: Most turtles from the Middle and Late Jurassic of Asia are referred to the newly defined clade Xinjiangchelyidae, a group of mostly shell-based, generalized, small to mid-sized aquatic froms that are widely considered to represent the stem lineage of Cryptodira. Xinjiangchelyids provide us with great insights into the plesiomorphic anatomy of crown-cryptodires, the most diverse group of living turtles, and they are particularly relevant for understanding the origin and early divergence of the primary clades of extant turtles.

Results: Exceptionally complete new xinjiangchelyid material from the ?Qigu Formation of the Turpan Basin (Xinjiang Autonomous Province, China) provides new insights into the anatomy of this group and is assigned to Xinjiangchelys wusu n. sp. A phylogenetic analysis places Xinjiangchelys wusu n. sp. in a monophyletic polytomy with other xinjiangchelyids, including Xinjiangchelys junggarensis, X. radiplicatoides, X. levensis and X. latiens. However, the analysis supports the unorthodox, though tentative placement of xinjiangchelyids and sinemydids outside of crown-group Testudines. A particularly interesting new observation is that the skull of this xinjiangchelyid retains such primitive features as a reduced interpterygoid vacuity and basipterygoid processes.

Conclusions: The homology of basipterygoid processes is confidently demonstrated based on a comprehensive review of the basicranial anatomy of Mesozoic turtles and a new nomenclatural system is introduced for the carotid canal system of turtles. The loss of the basipterygoid process and the bony enclosure of the carotid circulation system occurred a number of times independently during turtle evolution suggesting that the reinforcement of the basicranial region was essential for developing a rigid skull, thus paralleling the evolution of other amniote groups with massive skulls.

Show MeSH
Related in: MedlinePlus