28 - Skull ontogenetic trajectory variation and phylogeny in primates

Poster Board Number: 28
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Co-authors:

Jason Massey - Department of Anatomy and Developmental Biology, Centre for Human Anatomy Education, Biomedicine Discovery Institute - Monash University; Terrence Ritzman - Department of Anatomy - Midwestern University

Abstract Body : Ontogenetic trajectories based on geometric morphometric methods describe how organisms change in shape over time to become adults. Understanding how ontogenetic trajectories vary across the primate order can yield valuable insights into the selective pressures that produced highly variable adult primate skull form. Previous research focusing on narrow phylogenetic groups among primates (e.g., hominids, cercopithecines) identified significant variation in skull ontogenetic trajectories among these groups, suggesting that ontogenetic trajectories are not phylogenetically conserved. This has not been tested on a broader phylogenetic sample, however. Using geometric morphometric methods, growth trajectories were calculated from fifty-seven 3D skull landmarks as beta coefficients from multivariate regressions of shape variables on dental eruption stage. Pairwise angles between species’ trajectories, which represent differences in the pattern of shape change during development, and pairwise difference between magnitudes of species’ trajectories, which represent differences in the degree of shape change between species, were calculated for 12 primate species (including members of platyrrhines, cercopithecids, hominids, and strepsirrhines). Pairwise differences in mean centroid size between adults of each species as well as their phylogenetic distance (in millions of years) were also calculated. Multiple linear regression was used to determine whether phylogenetic distance is a significant predictor of pairwise trajectory angle and magnitude. Pairwise difference in adult centroid size was included in the models to account for allometric differences, and phylogenetic signal of trajectory magnitude was calculated as the Blomberg’s K statistic. Phylogenetic distance and pairwise centroid size were strong predictors of pairwise trajectory angle (r²= 0.69, p< 0.001), but the latter predictor was not significant. The model predicting pairwise trajectory magnitude was not significant and there was low phylogenetic signal in the trajectory magnitude data (K=0.64, p=0.076). While previous research on taxonomically narrower samples found no phylogenetic signal in skull ontogenetic trajectories, these results suggest that, in a broader taxonomic sample, more closely related species possess more similar cranial ontogenetic trajectories than more distantly related species, which supports the hypothesis that ontogenetic trajectories are influenced by phylogeny.