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A Middle Jurassic ‘sphenosuchian’ from China and the origin of the crocodylian skull

Nature volume 430, pages 10211024 (26 August 2004) | Download Citation

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Abstract

The skull of living crocodylians is highly solidified and the jaw closing muscles are enlarged1, allowing for prey capture by prolonged crushing between the jaws. Living species are all semi-aquatic, with sprawling limbs and a broad body that moves mainly from side-to-side2; however, fossils indicate that they evolved from terrestrial forms. The most cursorial of these fossils3,4,5,6 are small, gracile forms often grouped together as the Sphenosuchia, with fully erect, slender limbs; their relationships, however, are poorly understood5,7,8,9,10. A new crocodylomorph from deposits in northwestern China of the poorly known Middle Jurassic epoch possesses a skull with several adaptations typical of living crocodylians. Postcranially it is similar to sphenosuchians but with even greater adaptations for cursoriality in the forelimb. Here we show, through phylogenetic analysis, that it is the closest relative of the large group Crocodyliformes, including living crocodylians. Thus, important features of the modern crocodylian skull evolved during a phase when the postcranial skeleton was evolving towards greater cursoriality, rather than towards their current semi-aquatic habitus.

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Acknowledgements

Field work was supported by the National Geographic Society, the National Natural Science Foundation of China, the Jurassic Foundation, the Hilmar Sallee bequest, George Washington University and the Chinese Academy of Sciences. Study of the specimen was supported by the National Science Foundation Division of Earth Sciences. We thank D. Ma and W. Chen of the Changji Autonomous Prefecture and M. Zhu and X. Zhao of the IVPP for facilitating our work.

Author information

Author notes

    • Xing Xu

    Present address: Department of Paleontology, American Museum of Natural History, 79th Street at Central Park West, New York 10024, USA

Affiliations

  1. Department of Biological Sciences, George Washington University, Washington DC 20052, USA

    • James M. Clark
  2. Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, 142 Xiwai Street, Beijing, 100044, China

    • Xing Xu
    •  & Yuan Wang
  3. Department of Anatomical Sciences, Stony Brook University, Stony Brook, New York 11794, USA

    • Catherine A. Forster

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Competing interests

The authors declare that they have no competing financial interests.

Corresponding author

Correspondence to James M. Clark.

Supplementary information

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    Supplementary Information

    Containins the characters used in the phylogenetic analysis of Junggarsuchus and their distributions among 14 taxa of crocodylomorphs.

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https://doi.org/10.1038/nature02802

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