This dissertation research will investigate variation in the anatomical relationship of the facial skeleton and the braincase in anthropoid primates. Particularly, this study will test three hypotheses that represent non-mutually exclusive explanations for the position of the facial skeleton relative to the rest of the skull. The first two hypotheses posit that the position of the facial skeleton in anthropoid primates is determined by the anatomy of the brain -- by the overall size of the brain and the size of the temporal lobe, respectively. The third hypothesis represents an alternative to the notion that facial positioning in anthropoids is determined by the anatomy of the brain, and suggests instead that the size of the facial skeleton itself determines its position relative to the braincase. The hypotheses will be tested using data collected from digital radiographs of anthropoid skulls and MRI scans of anthropoid brains. The predictions of the hypotheses will be evaluated using metric and geometric morphometric methods, and phylogenetic comparative methods will be employed to adjust statistically for the evolutionary relationships among the taxa in the sample.

The results of this research will have important implications for understanding craniofacial architecture in anthropoid primates and will specific relevance for understanding the derived cranial form of Homo sapiens. The radiographs collected in the course of this dissertation will be published on a free online database that will be useful for physical anthropologists and other scientists and for educators. This project will also support the graduate training of a promising scientist.

Project Report

This project was aimed at testing hypotheses that related the anatomy of the brain to the morphology of the base of the skull and face in anthropoid primates (monkeys and apes). In so doing, this research provides important insights for understanding the overall influence that the brain has had on craniofacial form in this group. Moreover, this project contributes to the study of human evolution—in particular the evolution of modern Homo sapiens—by providing the basis upon which specific adaptive hypotheses about the origin of our species can be developed and tested. The hypotheses were tested using data from two sources: (1) radiographs of primate crania, and (2) data from MRI scans of primate brains. This research integrates osteological evidence collected from radiographs with data on the brain gleaned from MRI scans. Previous studies have investigated variation in primate brain anatomy using MRI scans, while other research has used radiographic data to explicate the relationship between the cranial base and the facial skeleton. To date, however, these lines of evidence have not been used in concert to examine how the anatomy of the brain influences the morphology of the cranial base and how this morphology, in turn, affects the position of the facial skeleton. This research therefore represents a novel, integrative approach to studying primate cranial architecture. The co-PI used funds from the DDIG to travel to Washington, DC to visit the National Museum of Natural History for four months (from March to July, 2012). During this visit, the co-PI produced digital radiographs of <1300 primate crania. In addition, he collected a barrage of linear measurements from theses crania. Additional data will also be collected directly from the digital radiographs in the upcoming months. MRI scans of primate brains have also been processed using software and a desktop computer purchased with funds from the NSF. Data from these scans will also be collected in the upcoming months and these data will be analyzed shortly thereafter. The co-PI also began development a free online radiograph database on which he will make available the radiographs amassed as part of this research project. In particular, the co-PI purchased a domain name and web storage for the website and developed the architecture for the database, including archiving, search, and browse functions. This website will be valuable to current and future scholars who want to study primate cranial anatomy and useful to educators who wish to integrate such information into their lessons. This website will also provide an important resource for researchers in parts of the world where obtaining high-quality radiographs is impractical or prohibitively expensive. The radiographs will be uploaded to the website in the next six months and the website will be available online by the summer of 2013. Funds from the Doctoral Dissertation Improvement Grant were also used to employ an undergraduate student assistant. This assistantship included training in data processing and collection from radiographs and MRI scans, data entry, and statistical analyses. Therefore, this study afforded an undergraduate student with experience that will be important to his training as a scientist and will help prepare him for graduate school or a professional career in anthropology or a related biological science. Finally, by including mentorship and scientific guidance from Dr. Jason Kaufman and members of his lab, this project furthered collaboration between the School of Human of Human Evolution and Social Change at Arizona State University and the Department of Anatomy at Midwestern University (Arizona School of Osteopathic Medicine).

National Science Foundation (NSF)
Division of Behavioral and Cognitive Sciences (BCS)
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Elizabeth Tran
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Arizona State University
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