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A Middle Triassic stem-turtle and the evolution of the turtle body plan

Nature volume 523, pages 584587 (30 July 2015) | Download Citation

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Abstract

The origin and early evolution of turtles have long been major contentious issues in vertebrate zoology1,2,3,4,5,6,7,8,9,10,11. This is due to conflicting character evidence from molecules and morphology and a lack of transitional fossils from the critical time interval. The 220-million-year-old stem-turtle Odontochelys from China12 has a partly formed shell and many turtle-like features in its postcranial skeleton. Unlike the 214-million-year-old Proganochelys from Germany and Thailand, it retains marginal teeth and lacks a carapace. Odontochelys is separated by a large temporal gap from the 260-million-year-old Eunotosaurus from South Africa, which has been hypothesized as the earliest stem-turtle4,5. Here we report a new reptile, Pappochelys, that is structurally and chronologically intermediate between Eunotosaurus and Odontochelys and dates from the Middle Triassic period (240 million years ago). The three taxa share anteroposteriorly broad trunk ribs that are T-shaped in cross-section and bear sculpturing, elongate dorsal vertebrae, and modified limb girdles. Pappochelys closely resembles Odontochelys in various features of the limb girdles. Unlike Odontochelys, it has a cuirass of robust paired gastralia in place of a plastron. Pappochelys provides new evidence that the plastron partly formed through serial fusion of gastralia3,13. Its skull has small upper and ventrally open lower temporal fenestrae, supporting the hypothesis of diapsid affinities of turtles2,7,8,9,10,14,15.

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Acknowledgements

We acknowledge the Schumann family for their continued support and granting access to the Vellberg quarry, and F. Ullmann, B. Rozynek, W. Kugler, T. Haubold, U. Günter, and M. Salomon for assistance in the field and for donating specimens to the Staatliches Museum für Naturkunde Stuttgart. N. Klein and T. Scheyer assisted with the histological interpretation of the thin-sections. T. Lyson provided the character-taxon matrix used in ref. 5. I. Rosin, N. Adorf, M. Kamenz, and K. Krämer prepared the material, and C. Wimmer-Pfeil prepared thin-sections. We thank D. Seegis, H. Hagdorn, W. Joyce, N. Klein, T. Lyson, J. Müller, O. Rieppel, and T. Scheyer for discussions.

Author information

Affiliations

  1. Staatliches Museum fur Naturkunde Stuttgart, Rosenstein 1, D-70191 Stuttgart, Germany

    • Rainer R. Schoch
  2. Department of Paleobiology, National Museum of Natural History, MRC 121, PO Box 37012, Washington, District of Columbia 20013-7012, USA

    • Hans-Dieter Sues

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Contributions

R.R.S. and H.-D.S. contributed equally to the research and the development of the manuscript; therefore their names are listed in alphabetical order.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Rainer R. Schoch or Hans-Dieter Sues.

P. rosinae is in the ZooBank database (http://zoobank.org/) with Life Science Identifier urn:lsid:zoobank.org:act:CDD54976-047F-43AA-80F4-9680DF78CD7B.

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    Supplementary information

    This file contains additional specimen and locality data, a list of characters and character-states, information on phylogenetic analysis and additional morphological detail on trunk ribs.

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https://doi.org/10.1038/nature14472

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