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Beyond the beak: Brain size and allometry in avian craniofacial evolution
Jesús Marugán-Lobón1,2, Sergio M Nebreda1, Guillermo Navalón1,3
1Unidad de Paleontología, Dpto. Biología, Universidad Autónoma de Madrid, Madrid, Spain.
Journal of Anatomy
|September 24, 2021
Summary
The Spatial Packing Hypothesis (SPH) predicts bird skull evolution, showing similarities to mammals. This architectural constraint, not just brain size, shapes avian craniofacial diversity.
Area of Science:
- Evolutionary biology
- Comparative anatomy
- Paleontology
Background:
- Avian skull evolution is diverse, with beak variation overshadowing other cranial changes.
- Mammalian skull evolution is explained by the Spatial Packing Hypothesis (SPH), an architectural constraint.
- The generality of SPH across tetrapods, including birds, remains unexamined.
Purpose of the Study:
- To investigate the applicability of the Spatial Packing Hypothesis (SPH) to avian skull evolution.
- To compare avian craniofacial variation patterns with those observed in mammals.
- To determine the influence of SPH, allometry, and encephalization on bird skull morphology.
Main Methods:
- Utilized three-dimensional geometric morphometrics on an interspecific sample of birds.
- Analyzed evolutionary variation trends in avian skulls, focusing on the face, cranial vault, and basicranium.
- Assessed the independence of SPH effects from allometry and volumetric encephalization.
Main Results:
- The dominant evolutionary variation in bird skulls aligns with SPH predictions.
- Avian craniofacial variation shows striking similarities to that of mammals.
- Allometric effects and volumetric encephalization are independent of SPH influence on skull morphology.
Conclusions:
- The Spatial Packing Hypothesis (SPH) provides a valid framework for understanding avian skull homoplasy.
- A general architectural constraint underlies skull evolution in birds and potentially across mammals.
- Encephalization and allometry are not the sole drivers of craniofacial evolution in birds.
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