Allometry and Evolution in the Galago Skull

Abstract

To probe the ontogenetic bases of morphological diversity across galagos, we performed the first clade-wide analyses of growth allometries in 564 adult and non-adult crania from 12 galagid taxa. In addition to evaluating if variation in galago skull form results from the differential extension/truncation of common ontogenetic patterns, scaling trajectories were employed as a criterion of subtraction to identify putative morphological adaptations in the feeding complex. A pervasive pattern of ontogenetic scaling is observed for facial dimensions across galagids, with 2 genera also sharing relative growth trajectories for masticatory proportions (Galago, Galagoides). As the facial growth series and adult data are largely coincidental, interspecific variation may result from character displacement and consequent selection for size differentiation among sister taxa. Derived configurations of the jaw joint and jaw muscle mechanical advantage in Otolemur and Euoticus appear to facilitate increased gape during scraping behaviors. Differences in aspects of masticatory growth and form characterizing these 2 genera highlight selection to uncouple shared ontogenetic patterns, which occurred via transpositions that retained ancestral scaling patterns. Due to the lack of increased robusticity of load-resisting mandibular elements in Otolemur and Euoticus, there is little evidence to suggest that exudativory in galagos results in correspondingly higher masticatory stresses.