Evolution of the avian skull
: evolutionary drivers of modern bird diversity

  • Guillermo Navalon

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


Encompassing more than 11,000 species, birds are the most speciose group of tetrapods in modern-world ecosystems. The modern radiation of birds (Neornithes) originated in the Mesozoic and greatly radiated in disparity following the K-Pg extinction, a radiation which is often believed to have been primarily driven by adaptation in response to ecological opportunity after this biotic crisis. This assumption largely rests on the presumption that the anatomy in birds, particularly the large variety of beak forms, is very correlated with their ecologies, particularly feeding ecology. In this thesis, this presumption is tested in a broad macroevolutionary scale for the first time. I find that this relationship is weaker and more complex than often assumed, suggesting that the diversification of beak morphologies in birds was likely shaped by a more complex set of evolutionary drivers than feeding adaptation, likely involving both extrinsic and intrinsic factors. Consequently, the roles of other intrinsic factors in craniofacial evolution are explored within some selected lineages of modern birds. First, I explore the patterns and strength of the coevolution between the beak and the rest of the skull (cranial integration), across all the lineages of landbirds (Inopinaves) and how these associations affected their craniofacial macroevolution. I find that variations in cranial integration had important implications for cranial evolution, specifically for the two classic avian adaptive radiations: Darwin’s finches and Hawaiian honeycreepers. Secondly, I explore craniofacial shape variation over evolution and development in Strisores. My results suggest that evolutionary changes in development played a significant role in shaping macroevolution in this clade of birds. Finally, over this thesis geometric morphometrics and phylogenetic comparative methods are extensively used. I show some current limitations of these methods concerning the quantification of covariation patterns (integration and modularity). I propose a pipeline for identifying potential issues and offer some preliminary novel solutions to overcome them.
Date of Award25 Jun 2019
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorEmily J Rayfield (Supervisor), Jesús Marugán-Lobón (Supervisor) & Jen A. Bright (Supervisor)


  • birds
  • macroevolution
  • shape
  • skull
  • geometric morphometrics
  • adaptation
  • constraint
  • integration
  • phylogenetic comparative methods
  • development

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