Birds show tremendous ecological disparity in spite of strong biomechanical constraints imposed by flight. Modular skeletal evolution is generally accepted to have facilitated this, with distinct body regions showing semi-independent evolutionary trajectories. However, this hypothesis has received little scrutiny. We analyse evolutionary modularity and ecomorphology using three-dimensional data from across the entire skeleton in a phylogenetically broad sample of extant birds. We find strongly modular evolution of skeletal element sizes within body regions (head, trunk, forelimb and hindlimb). However, element shapes show substantially less modularity, have stronger relationships to ecology, and provide evidence that ecological adaptation involves coordinated evolution of elements across different body regions. This complicates the straightforward paradigm in which modular evolution facilitated the ecological diversification of birds. Our findings suggest the potential for undetected patterns of morphological evolution in even well-studied groups, and advance the understanding of the interface between evolutionary integration and ecomorphology.
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R version 3.63 was employed to run the analyses. The packages and functions used are described in detail in the Methods with citations. The codes written by assembling these pre-built functions are available upon request.
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For access to specimens, we thank J. White and J. Cooper (NHMUK), J. Hinshaw (UMMZ), M. Lowe and M. Brooke (UMZC), M. Carnall and E. Westwig (OUMNH), K. Zyskowski (YPM), and B. Marks and J. Bates (FMNH). For access to CT scanning facilities, we thank K. Smithson (Cambridge Biotomography Centre); T. Davies, B. Moon and L. Martin-Silverstone (University of Bristol); V. Fernandez (Natural History Museum); A. Neander and Z.-X. Luo (University of Chicago PaleoCT); and M. Friedman (University of Michigan). We thank E. Griffiths, S. Wright, S. Poindexter, A. Wolniewicz and S. Evers for segmenting digital bone models from the CT scan data. We acknowledge G. Navalón for reviewing our manuscript and making key suggestions concerning the presentation of our figures. Funding statement: This work was funded by the European Union’s Horizon 2020 research and innovation programme 2014–2018 under grant agreement no. 677774 (European Research Council Starting Grant: TEMPO). Grant no. 677774 applies to the work of R.B.J.B. and A.B.
The authors declare no competing interests.
Peer review information Nature Ecology & Evolution thanks T. Alexander Dececchi and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.
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Orkney, A., Bjarnason, A., Tronrud, B.C. et al. Patterns of skeletal integration in birds reveal that adaptation of element shapes enables coordinated evolution between anatomical modules. Nat Ecol Evol 5, 1250–1258 (2021). https://doi.org/10.1038/s41559-021-01509-w