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An ancestral turtle from the Late Triassic of southwestern China

Nature volume 456, pages 497501 (27 November 2008) | Download Citation

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Abstract

The origin of the turtle body plan remains one of the great mysteries of reptile evolution. The anatomy of turtles is highly derived, which renders it difficult to establish the relationships of turtles with other groups of reptiles. The oldest known turtle, Proganochelys from the Late Triassic period of Germany1, has a fully formed shell and offers no clue as to its origin. Here we describe a new 220-million-year-old turtle from China, somewhat older than Proganochelys, that documents an intermediate step in the evolution of the shell and associated structures. A ventral plastron is fully developed, but the dorsal carapace consists of neural plates only. The dorsal ribs are expanded, and osteoderms are absent. The new species shows that the plastron evolved before the carapace and that the first step of carapace formation is the ossification of the neural plates coupled with a broadening of the ribs. This corresponds to early embryonic stages of carapace formation in extant turtles, and shows that the turtle shell is not derived from a fusion of osteoderms. Phylogenetic analysis places the new species basal to all known turtles, fossil and extant. The marine deposits that yielded the fossils indicate that this primitive turtle inhabited marginal areas of the sea or river deltas.

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Acknowledgements

We thank Z. Tang for his help in collecting the specimens; J. Ding and H. Zhou for preparing the specimens; and W. Gao for taking the photos. C.L. and L.-T.W. were supported by the Major Basic Research Projects (2006CB806400) of the Ministry of Science and Technology of China, the National Natural Science Foundation (40772015, 40121202) of China (NNSFC) and a special grant for fossil excavation and preparation of the Chinese Academy of Sciences. X.-C.W. was supported by grants from the Canadian Museum of Nature (RS 34), NNSFC 40772015 and the CAS/SAFEA International Partnership Program for Creative Research Teams. O.R. was supported by a stipend from M. Tang.

Author Contributions C.L. designed the project. C.L., X.-C.W., O.R., L.-T.W. and L.-J.Z. performed the research. C.L., X.-C.W. and O.R. contributed to the writing.

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Affiliations

  1. Laboratory of Evolutionary Systematics of Vertebrates, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of SciencesPO Box 643, Beijing 100044, China

    • Chun Li
  2. Canadian Museum of Nature, PO Box 3443, Station D, Ottawa, Ontario K1P 6P4, Canada

    • Xiao-Chun Wu
  3. Department of Geology, The Field Museum, 1400 South Lake Shore Drive, Chicago, Illinois 60605-2496, USA

    • Olivier Rieppel
  4. Geological Survey of Guizhou Province, Guiyang 550005, China

    • Li-Ting Wang
  5. Zhejiang Museum of Nature History, Hangzhou 310012, China

    • Li-Jun Zhao

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Corresponding authors

Correspondence to Chun Li or Xiao-Chun Wu.

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https://doi.org/10.1038/nature07533

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