A quantitative assessment of infraorbital morphology in Homo

Abstract

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.

Zygomaticomaxillary Morphology and Maxillary Sinus Form and Function: How Spatial Constraints Influence Pneumatization Patterns among Modern Humans

“…Our previous study found more laterally extended sinuses were clearly associated with aspects of lateral facial morphology, most notably, anteriorly projecting zygomatics. However, as we noted in our previous study, exceedingly anteriorly projecting zygomatics are commonly considered a distinctive characteristic of Asian and Asian‐derived populations (Woo and Morant, ; Howells, ; Hanihara, ; Maddux, ; Evteev et al, ). Because it was our Siberian/Arctic circumpolar sample that exhibited more laterally extending maxillary sinuses, we hypothesized that the association between lateral sinus extension and anterior zygomatic position might have been driven by the shared Asian ancestry of our circumpolar sample.…”

“…As previously noted by Zollikofer et al (), fossil hominins with large zygomaticomaxillary interfaces typically exhibit maxillary sinuses that extend laterally to a considerable degree (in some cases excavating beyond the zygomaxillary suture). Unfortunately, the human fossil record is lacking in adult archaic (i.e., non‐ Homo sapiens ) specimens with relatively small zygomaticomaxillary interfaces (Pope, ; Maddux, ; Freidline et al, ), thus limiting potential comparisons. Still, it is worth noting that several studies of facial ontogeny in fossil Homo (Minugh‐Purvis, ; Maureille and Bar, ; Freidline et al, ) indicate that the relatively large zygomaticomaxillary proportions of archaic humans appeared early in post‐natal development, suggesting that these individuals would have likely had ample space for lateral sinus pneumatization to occur during growth and development.…”

“…Sub‐Saharan Africans exhibited narrower maxillary sinuses in conjunction with both wide nasal cavities and more posteriorly retracted zygomatics, while circumpolar individuals tended to exhibit wider maxillary sinuses in conjunction with narrower noses and lateral faces that project more anteriorly. Furthermore, anteriorly‐projecting or “flaring” zygomatics and straight zygomatic crests are commonly considered characteristics specific to Asian‐derived populations (see Woo and Morant, ; Howells, ; Hanihara, ; Maddux, ; Evteev et al, ). As a consequence, it remains unclear whether our previous finding of an association between maxillary sinus breadth and zygomatic anterior–posterior positioning was predominantly due to our circumpolar sample exhibiting a derived lateral facial morphology, or whether our results actually reflected a more generalized human pattern.…”