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The multifactorial nature of beak and skull shape evolution in parrots and cockatoos (Psittaciformes)

Bright, Jen A.; Marugán-Lobón, Jesús; Rayfield, Emily J.; Cobb, Samuel N.


Jesús Marugán-Lobón

Emily J. Rayfield

Samuel N. Cobb


© 2019 The Author(s). Background: The Psittaciformes (parrots and cockatoos) are characterised by their large beaks, and are renowned for their ability to produce high bite forces. These birds also possess a suite of modifications to their cranial architecture interpreted to be adaptations for feeding on mechanically resistant foods, yet the relationship between cranial morphology and diet has never been explicitly tested. Here, we provide a three-dimensional geometric morphometric analysis of the developmental and biomechanical factors that may be influencing the evolution of psittaciformes' distinctive cranial morphologies. Results: Contrary to our own predictions, we find that dietary preferences for more- or less- mechanically resistant foods have very little influence on beak and skull shape, and that diet predicts only 2.4% of the shape variation in psittaciform beaks and skulls. Conversely, evolutionary allometry and integration together predict almost half the observed shape variation, with phylogeny remaining an important factor in shape identity throughout our analyses, particularly in separating cockatoos (Cacatuoidea) from the true parrots (Psittacoidea). Conclusions: Our results are similar to recent findings about the evolutionary trajectories of skull and beak shape in other avian families. We therefore propose that allometry and integration are important factors causing canalization of the avian head, and while diet clearly has an influence on beak shape between families, this may not be as important at driving evolvability within families as is commonly assumed.


Bright, J. A., Marugán-Lobón, J., Rayfield, E. J., & Cobb, S. N. (2019). The multifactorial nature of beak and skull shape evolution in parrots and cockatoos (Psittaciformes). BMC evolutionary biology, 19(1), Article 104.

Journal Article Type Article
Acceptance Date May 6, 2019
Online Publication Date May 17, 2019
Publication Date 2019-12
Deposit Date Nov 28, 2019
Publicly Available Date Nov 28, 2019
Journal BMC Evolutionary Biology
Print ISSN 1471-2148
Electronic ISSN 1471-2148
Publisher Springer Verlag
Peer Reviewed Peer Reviewed
Volume 19
Issue 1
Article Number 104
Keywords Birds; Geometric morphometrics; Allometry; Integration; Feeding; Parrots
Public URL


Published article (2.8 Mb)

Copyright Statement
© The Author(s). 2019. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (, which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated.

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