Decelerated dinosaur skull evolution with the origin of birds

Ryan Felice*, Akinobu Watanabe, Andrew R Cuff, Michael Hanson, Bhart-Anjan Bhullar, Emily J Rayfield, Lawrence, M Witmer, Mark Norell, Anjali Goswami

*Corresponding author for this work

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Abstract

The evolutionary radiation of birds has produced incredible morphological variation, including a huge range of skull form and function. Investigating how this variation arose with
respect to non-avian dinosaurs is key to understanding how birds achieved their remarkable
success after the Cretaceous–Paleogene extinction event. Using a high-dimensional geometric morphometric approach, we quantified the shape of the skull in unprecedented detail
across 354 extant and 37 extinct avian and non-avian dinosaurs. Comparative analyses
reveal fundamental differences in how skull shape evolved in birds and non-avian dinosaurs.
We find that the overall skull shape evolved faster in non-avian dinosaurs than in birds
across all regions of the cranium. In birds, the anterior rostrum is the most rapidly evolving
skull region, whereas more posterior regions—such as the parietal, squamosal, and quadrate—exhibited high rates in non-avian dinosaurs. These fast-evolving elements in dinosaurs are strongly associated with feeding biomechanics, forming the jaw joint and
supporting the jaw adductor muscles. Rapid pulses of skull evolution coincide with changes
to food acquisition strategies and diets, as well as the proliferation of bony skull ornaments.
In contrast to the appendicular skeleton, which has been shown to evolve more rapidly in
birds, avian cranial morphology is characterised by a striking deceleration in morphological
evolution relative to non-avian dinosaurs. These results may be due to the reorganisation of
skull structure in birds—including loss of a separate postorbital bone in adults and the emergence of new trade-offs with development and neurosensory demands. Taken together, the
remarkable cranial shape diversity in birds was not a product of accelerated evolution from
their non-avian relatives, despite their frequent portrayal as an icon of adaptive radiations.
Original languageEnglish
Article numbere3000801
Number of pages25
JournalPLoS Biology
Volume18
Issue number8
DOIs
Publication statusPublished - 18 Aug 2020

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    Felice, R., Watanabe, A., Cuff, A. R., Hanson, M., Bhullar, B-A., Rayfield, E. J., Witmer, L. M., Norell, M., & Goswami, A. (2020). Decelerated dinosaur skull evolution with the origin of birds. PLoS Biology, 18(8), [e3000801]. https://doi.org/10.1371/journal.pbio.3000801