Eel-like swimming in the earliest ichthyosaurs (original) (raw)

Nature volume 382, pages 347–348 (1996)Cite this article

Abstract

ICHTHYOSAURS are extinct marine reptiles, probably belonging to the Diapsida1, that ranged from the Early Triassic to Late Cretaceous2,3. Post-Triassic ichthyosaurs achieved the highest level of aquatic adaptation among reptiles4, with a streamlined body, lunate tail and a dorsal fin, features exemplified today by thunniform (tuna-like) fishes. However, little is known of how such a body plan evolved from a terrestrial diapsid. Here we report the most complete specimen of the oldest known ichthyosaur, Chensaurus, representing a transition between the two body plans. The specimen, which has a partial skin impression, has a small caudal fin, a long and narrow body, and a high presacral vertebral count. These features all suggest an anguilliform swimming mode. Later ichthyosaurs retained the high vertebral count, but overcame the high swimming costs of this plesiomorphy, achieving a rigid tunniform bauplan by evolving discoidal vertebrae, and a deep fusiform body. Chensaurus therefore seems to be an evolutionary intermediate between the shorter-bodied terrestrial stock from which the group evolved, and advanced thunniform ichthyosaurs.

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Authors and Affiliations

  1. Department of Zoology, University of Toronto, Toronto, Ontario, M5S 1A1, Canada
    R. Motani & C. McGowan
  2. Department of Paleobiology, Royal Ontario Museum, Toronto, Ontario, M5S 2C6, Canada
    R. Motani & C. McGowan
  3. Institute of Vertebrate Paleontology and Paleoanthropology, PO Box 643, Beijing, 100044, China
    You H.

Authors

  1. R. Motani
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  2. You H.
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  3. C. McGowan
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Motani, R., H., Y. & McGowan, C. Eel-like swimming in the earliest ichthyosaurs.Nature 382, 347–348 (1996). https://doi.org/10.1038/382347a0

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