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Evolutionary origins of the avian brain

Nature volume 501, pages 9396 (05 September 2013) | Download Citation

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Abstract

Features that were once considered exclusive to modern birds, such as feathers and a furcula, are now known to have first appeared in non-avian dinosaurs1. However, relatively little is known of the early evolutionary history of the hyperinflated brain that distinguishes birds from other living reptiles and provides the important neurological capablities required by flight2. Here we use high-resolution computed tomography to estimate and compare cranial volumes of extant birds, the early avialan Archaeopteryx lithographica, and a number of non-avian maniraptoran dinosaurs that are phylogenetically close to the origins of both Avialae and avian flight. Previous work established that avian cerebral expansion began early in theropod history and that the cranial cavity of Archaeopteryx was volumetrically intermediate between these early forms and modern birds3,4. Our new data indicate that the relative size of the cranial cavity of Archaeopteryx is reflective of a more generalized maniraptoran volumetric signature and in several instances is actually smaller than that of other non-avian dinosaurs. Thus, bird-like encephalization indices evolved multiple times, supporting the conclusion that if Archaeopteryx had the neurological capabilities required of flight, so did at least some other non-avian maniraptorans. This is congruent with recent findings that avialans were not unique among maniraptorans in their ability to fly in some form5,6.

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Acknowledgements

Funding for this project was provided by a NSF DDIG (DEB 0909970) to A.M.B. and M.A.N., NSF IIS-0208675 and EAR-0948842 to T.B.R. and a Columbia University International Travel Fellowship to A.M.B. The University of Texas Computed Tomography Facility and the AMNH MIF helped with computed tomographic scanning and processing imagery. M. Colbert, P. Gignac, D. Ksepka, J. Flynn and J. Meng read and provided useful comments on the text.

Author information

Author notes

    • Amy M. Balanoff

    Present address: Department of Anatomical Sciences, Stony Brook University School of Medicine, Stony Brook, New York 11794, USA.

Affiliations

  1. American Museum of Natural History, Division of Paleontology, New York, New York 10024, USA

    • Amy M. Balanoff
    • , Gabe S. Bever
    •  & Mark A. Norell
  2. Columbia University, Department of Earth and Environmental Sciences, New York, New York 10027, USA

    • Amy M. Balanoff
  3. New York Institute of Technology, College of Osteopathic Medicine, Old Westbury, New York 11568, USA

    • Gabe S. Bever
  4. Jackson School of Geosciences, The University of Texas at Austin, Austin, Texas 78712, USA

    • Timothy B. Rowe

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Contributions

A.M.B., G.S.B. and M.A.N. designed the study. A.M.B. wrote the paper, performed data entry and analytical work, and prepared figures. G.S.B. assisted in data interpretation and helped to write the paper. T.B.R. contributed computed tomography data and assisted in data interpretation. M.A.N. provided computed tomography data and assisted in writing the paper.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Amy M. Balanoff.

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    Supplementary Information

    This file contains Supplementary Figures 1- 3, Supplementary Tables 1 -5 and Supplementary References.

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https://doi.org/10.1038/nature12424

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