Features of the infraorbital region, such as infraorbital surface topography, infraorbital surface orientation, and curvature of the zygomaticoalveolar crest, have long played a prominent role in phylogenetic analyses of Homo. However, there is currently considerable debate regarding the phylogenetic reliability of infraorbital characters, as numerous researchers have questioned the degree to which these features are morphologically independent of one another and facial size. These questions stem largely from methodological limitations for accurately quantifying the curvilinear morphology of the infraorbital surface and zygomaticoalveolar crest, which have significantly impeded the ability to discern patterns of infraorbital integration and allometry.In this study, infraorbital surface and zygomaticoalveolar crest morphology are precisely assessed, through geometric morphometric methodologies well-suited for quantifying complex curvilinear structures, in a large sample of recent (n = 303) and fossil (n = 71) Homo. Once quantified, measures of infraorbital surface topography, infraorbital surface orientation and zygomaticoalveolar crest curvature are further evaluated for intercorrelation and allometry in order to more fully evaluate the morphological independence of commonly cited infraorbital characters. The results of this study indicate that most aspects of infraorbital surface topography, infraorbital surface orientation and zygomaticoalveolar crest curvature are significantly correlated with facial size across Homo. Moreover, certain aspects of infraorbital shape, such the degree of infraorbital surface depression and the overall curvature of the zygomaticoalveolar crest, appear to show additional, size-independent, intercorrelations, suggesting they form an integrated "infraorbital complex." In light of these results, the use of infraorbital characters as separate independent characters in Copyright by SCOTT DAVID MADDUX 2011 All Rights Reserved Graduate College ii For Tressaiii ACKNOWLEDGMENTS There are numerous people and institutions without whose help this dissertation would not have been possible, and to whom I consequently owe a great debt of gratitude.First, I would like to thank Dr. Robert Franciscus, who has served as my advisor throughout graduate school at the University of Iowa. From the beginning he has been an enlightening teacher, conscientious mentor and trustworthy advisor, who has always given freely of his time, knowledge and resources. Without his expertise, patience and encouragement this dissertation would have been an insurmountable undertaking. It has been a truly immeasurable learning experience working in his lab, and I am grateful for having had the privilege of studying under such an exemplary paleoanthropologist.