Anatomical Network Analysis of Primate Skull Morphology

Abstract

A core question driving studies of primate evolution is how phenotypic variation in the skull arose without compromising vital functions and structures of the head. Alongside morphogenetic processes, mechanical forces influence head development, e.g. bone connections are primary growth sites and force-diffusors. Yet the influence that physical constraints (i.e., bone-bone contacts) have on the developmental plasticity and thus evolvability of skull form is unclear. Anatomical Network Analysis (AnNA) is a new way to query this influence by measuring presence, strength, direction, symmetry and density of connections among skull bones. Here we present AnNA of interaction among skull bones in twenty extant primate taxa, including humans, chosen to represent the phenotypic breadth of head variation. AnNA found that connectivity was more variable for the facial bones, which divided into three modules (midfacial, palatal, rostral) in non-human primates (a single module in humans); and more conserved for the cranial bones, which formed a single module in all primates but varied in specific bone-bone connections in Hominidae. Network models of the skull did not carry significant phylogenetic signals, stressing the influence of other factors in the evolution of skull anatomy. Our AnNA results also suggested that modularity and complexity do not evolve in a positive feedback relationship in the primate skull. Natural Sciences & Engineering Research Council of Canada (JCB); Howard University (RD); Cavanilles Institute of Biodiversity & Evolutionary Biology (BE-A, DR-G)