Collaborative Research: Integrative Investigation of the Evolution and Biomechanics of Mandibular Form in Hominids

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Among the fundamental questions about human origins is how our hominin ancestors lived. This study uses a multidisciplinary approach (paleontology, paleoecology, comparative anatomy, experimental biology) to ask questions about how extinct populations of hominins behaved on their natural landscapes. Specifically, the investigators will analyze lower jaws (mandibles), among the most commonly represented parts of the skeleton in the early human fossil record, of modern great apes and two early species of extinct hominins (Autralopithecus), to understand how the structure of the mandible is related to changes in feeding behavior and diet. The research will provide new data about how changes in diet and feeding behavior transformed our anatomy across time, permitting more robust explanations of the processes by which we became human. Broader impacts will include undergraduate, graduate and postdoctoral training in the latest analytical techniques for fossil analyses; outreach to primary and secondary school science teachers and students using hands-on experiences and web-based content designed to enhance teaching and learning about human origins; and the production of a unique collection 3D data for modern apes and rare fossil specimens that will be available to the scientific community.Mandibles are the most common element in the hominin fossil record after teeth; they are used to diagnose species, test phylogenetic hypotheses, and infer feeding behavior and diet. However, extensive theoretical and experimental work on extant primates has not clarified which aspects of variation in mandibular form are related to variation in the positions of the tooth row, jaw muscles and jaw joint, which are related to the mandible's resistance to internal forces, and how these relate to feeding behavior and diet. Furthermore, the classical consensus on the relationship between dentognathic morphology and diet in Plio-Pleistocene hominins - adaptation to processing mechanically resistant foods - has been challenged by recent inferences from dietary isotopes, occlusal microwear, and finite element modeling, which do not converge on a shared view of early hominin diets and feeding behavior. This lack of consensus is especially glaring in light of the rich fossil record of mandibles for the Australopithecus anamensis-A. afarensis lineage (4.2-3.0 Ma), which documents clear changes in dentognathic morphology and carbon-isotope signatures over time. The primary focus of the proposed research is an integrative investigation of how spatial and mechanical determinants of mandibular form track change in diet and feeding behavior in extant hominids (great apes and humans) and early Australopithecus. The research is organized under three specific aims: 1. Quantifying and comparing the location, magnitude and nature of external and internal morphological variation in mandibles of extant (Homo, Pongo, Pan, and Gorilla) and fossil (A. anamensis, A. afarensis) hominids via computed tomography and geometric morphometrics; 2. Testing specific hypotheses about the biomechanical significance of variation in hominid mandibular morphology via finite-element models; and 3. Evaluating the extent to which spatial positioning of masticatory system components (tooth row, jaw joint, and muscle attachment points) explain variation in mandibular morphology across extant hominids and early Australopithecus. The project will provide new data on the structural and functional determinants of early hominin mandibular morphology, to help identify the factors that drove these morphological changes and allow tests of adaptive hypotheses about the early evolution of the genus.