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Tetrapod-like middle ear architecture in a Devonian fish

Nature volume 439, pages 318321 (19 January 2006) | Download Citation

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Abstract

Few fossils show the incipient stages of complex morphological transformations1. For example, the earliest stages in the remodelling of the spiracular tract and suspensorium (jaw suspension) of osteolepiform fishes2,3,4 into the middle ear of tetrapods have remained elusive3. The most primitive known tetrapods show a middle ear architecture that is very different from osteolepiforms such as Eusthenopteron3, with little indication of how this transformation took place. Here we present an analysis of tetrapod middle ear origins that is based on a detailed study of Panderichthys, the immediate sister taxon of tetrapods. We show that the spiracular region is radically transformed from osteolepiforms and represents the earliest stages in the origin of the tetrapod middle ear architecture. The posterior palatoquadrate of Panderichthys is completely tetrapod-like and defines a similarly tetrapod-like spiracular tract. The hyomandibula has lost its distal portion, representing a previously unrecognized advance towards a stapes-like morphology. This spiracular specialization suggests that the middle ear of early tetrapods evolved initially as part of a spiracular breathing apparatus5,6.

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Acknowledgements

We thank E. Luksevics and I. Zupins for access to specimens; T. Rowe for computed tomography scan work; M. Arsenault and S. Desbiens for providing the Eusthenopteron specimen and, together with T. Rowe, for allowing us to publish these early results. M.D.B is supported by a Fonds québecois de la recherche sur la nature et les technologies (FQRNT) bourse de maîtrise (graduate scholarship). P.E.A. is supported by a professorship and research grant from Vetenskapsrådet.

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  1. Subdepartment of Evolutionary Organismal Biology, Department of Physiology and Developmental Biology, Evolutionary Biology Centre, Uppsala University, Norbyv 18A, SE-752 36 Uppsala, Sweden

    • Martin D. Brazeau
    •  & Per E. Ahlberg

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Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.

Corresponding author

Correspondence to Martin D. Brazeau.

Supplementary information

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    Supplementary Notes

    This contains an additional description of the Panderichthys specimen from this work.

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https://doi.org/10.1038/nature04196

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