The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)

Morphological variation and the role of allometry in the Galagonidae cranium


Anthropology, University College London

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To gain an insight into the selection pressures causing both inter- and intra-specific variation within the Galagonidae cranium a total of 65 3D landmarks were collected from 740 crania, belonging to 8 species, across 3 genera, using a Microscribe X digitiser. In order to establish the extent to which shape variation is the result of allometry (shape constrained by size) the data were subjected to Generalised Procrustes and Principal Components (PC) analyses. Phylogenetic Generalised Least Square (PGLS) regressions were then conducted in R (version 2.13.1) between species average PC scores and centroid sizes. PGLS controls for phylogenetic non-independence and in this instance a composite phylogenetic tree, generated using the 10K trees website (version 3), was used. The full landmark composition showed significant negative allometry for PC1, with allometric scaling explaining 22.8% of the total residual variance between species, after isometric scaling. The shape change ascribed to PC1 represents a dorso-ventral flattening of the skull, in both the face and the calvarium, as centroid size increases. Significant negative allometry was also found when functional/developmental modules of the skull, namely the face, basicranium, vault and zygomatic –pterygoid, were examined separately. The remaining shape variation in the Galagonidae cranium not accounted for by size or phylogenetic effects are discussed in the context of environmental and geographical variation. The Galagonidae represent an ideal family in which to study the interaction between morphology, phylogeny, size and environment, ranging, as they do, across almost all of sub-Saharan Africa, covering an extensive range of habitats and size.

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