Macroevolution of Primate Skull Shape: Combining Geometric Morphometrics and Phylogenetic Comparative Methods
Primates span incredible behavioral and ecological diversity, and this diversity is reflected in the shape of the skull. This dissertation asks two questions surrounding the evolution of primate skull shape: 1) what are the macroevolutionary correlates of primate skull shape? And 2) what is the pattern of phenotypic integration in the primate skull at a macroevolutionary scale? To address these questions, I compiled a broad comparative dataset of anatomical landmarks identified from 3D scans of primate skulls and analyzed this data using statistical methods that combine geometric morphometrics and phylogenetic comparative methods. To investigate the macroevolutionary correlates of skull shape, I used multivariate phylogenetic generalized linear models to test for relationships between skull shape and several variables that are predicted to be correlated with skull shape: allometry, typical diet, tree gouging behavior, activity pattern, and sexual dimorphism. I found strong phylogenetic signal for primate skull shape, confirming the need for phylogenetic comparative methods. Allometry was a significant predictor of skull shape, with larger primates having relatively small, convergent orbits, and anteroposteriorly short skulls compared to small primates. Sexual dimorphism was associated with a dramatically lengthened rostrum, probably to facilitate a large gape in aggressive displays. Folivory was associated with deeper mandibles, which may improve mechanical advantage and strain resistance. To investigate patterns of phenotypic integration in the skull, I performed hierarchical clustering analyses on phylogenetically corrected inter-landmark covariance matrices. In contrast to previous research, I did not find evidence for distinct phenotypic modules in the primate skull, and I argue that this discrepancy is due to methodological shortcomings of past research that biased results towards identifying different anatomical regions as discrete modules. This dissertation represents one of the first investigations of primate skull shape at a macroevolutionary scale, and demonstrates that the combination of geometric morphometrics and phylogenetic comparative methods can yield novel insights into evolutionary morphology.
Evolution & development
phylogenetic comparative methods
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