Understanding Primate Mandibular Symphyseal Fusion: Function, Integration, And Ontogeny

Abstract

Understanding the function-shape relationships of the primate masticatory apparatus has been a focus of anthropological research for many decades. One particular feature of the masticatory apparatus, mandibular symphyseal fusion, is investigated in this work because symphyseal fusion has the potential to provide important information on masticatory function and mandibular fragments are often preserved in the fossil record. Regardless of the attention this anatomical feature has received, a complete understanding of the underlying mechanisms driving the evolution of symphyseal fusion remains elusive. The research presented in this dissertation tackles this dilemma by investigating the functional, integrative, and ontogenetic elements of symphyseal fusion. Function and morphology are linked through innovative approaches using the burgeoning geometric morphometric toolkit to challenge previously held notions about mandibular symphyseal fusion and generate new hypotheses. Ultimately, this work acknowledges similar underlying mechanisms for symphyseal fusion in different primate lineages which were previously thought to be different, questions the utility of symphyseal fusion for reconstructing evolutionary relationships of primates, and finds potential evidence for the independent evolution of symphyseal fusion within the crown anthropoid clade.