Expanding our horizons in understanding brain and dietary evolution in Primates and their kin

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The evolution of the diet is central to the process of primate origins. All of the competing scenarios for primate origins have a dietary component: visual predation focusing on adaptations for insectivory; terminal branch feeding involving an expansion of the arboreal dietary niche to include more fruit; and the grasp-leaping hypothesis, which incorporates a shift to greater herbivory in early primate evolution. Diet is of particular importance in understanding the evolution of the enlarged and complex primate brain. Building such a brain requires access to high energy food, while retrieving such broadly dispersed and irregularly available foodstuffs (e.g., fruit) requires greater degrees of processing power. Although analyses of modern primates have supported the important role of diet in brain evolution, they necessarily simplify the origin of primates down to a single node. The fossil record demonstrates that there were many lineages of stem primates, making it clear that the story is much more complex than the idealized version implied by such studies. Although there have been strides in recent years, there are still several lineages of early primates for which no quantitative work has been done to estimate aspects of diet. A critical component of this shortfall is that early primates have patterns of adaptations not found among living primates, meaning that living members of the order are insufficient models for reconstructing diet in those groups. The current study will seek to fill some of these gaps by considering a much broader range of model taxa and by using cutting edge dental topographic methods to allow for precise quantification of dental form. This study will also seek to expand the types of information that can be collected and compared with respect to the early evolution of the brain in primates. The strong evidence for rampant parallelism in primate brain size evolution implies that studies that are limited to living taxa will be constrained in reconstructing the size and shape of the brain in the common ancestor of all primates. This underscores the importance of fossils to an understanding of the early stages of primate brain evolution. Since the brain does not fossilize, the data available from even the best-preserved fossils is limited to the imprint of the brain preserved on the internal surface of the cranium (i.e., the endocast). The current study will seek to use geometric morphometric and DiceCT methods to expand the information about changing shape and function that can be extracted from such endocasts. Ultimately, the goal of this study will be to amass a dataset that will allow for a synthetic consideration of how shifting diets are aligned (or not) with changes in brain size and shape, using a phylogenetic framework that incorporates both fossil and extant members of Primates, and of closely related groups.