The Primate Ectotympanic Tube: Correlates of Structure, Function, and Development
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THE PRIMATE ECTOTYMPANIC TUBE: CORRELATES OF STRUCTURE, FUNCTION, AND DEVELOPMENT by Ellen Elise Irwin Fricano A dissertation submitted to Johns Hopkins University in conformity with the requirements for the degree of Doctor of Philosophy Baltimore, MD Submission Date: October 2018 i ABSTRACT The primate ectotympanic bone form is frequently used in anthropology as a discrete characteristic with strong phylogenetic signaling among primates; however, the proximate mechanism by which this variation operates has not been shown. Some primates (catarrhines and tarsiers) have been described as having an elongate bony ectotympanic tube; others (strepsirrhines and platyrrhines) maintain just a ring of bone. While some functional theories have been suggested, the present dissertation project suggests that the variation in the ectotympanic bones is more likely a morphological response to overall cranial shape. Structural correlates were identified using geometric morphometric methods in two sets of analyses, one using large intraspecific sample sizes of two catarrhine species and the other looking across all primates. The relative length of the ectotympanic bone in both of these analyses is tested for correlations with overall cranial structure. Two fossil catarrhines are included that have been noted for their unusual ectotympanic bones: Aegyptopithecus zeuxis and Pliopithecus vindobonensis. This dissertation project also illustrates the growth of the ectotympanic bone in primates via an in-depth discussion of the human, catarrhine, tarsier, and lorisiform growth patterning. This subproject is presented using non-metric analyses and qualitative description. Across analyses, these three subprojects show that the relative length of the ectotympanic tube is most correlated and potentially driven by the width of the cranium relative to the length of the cranium. Relatively wide crania and wide brains tend to present with long ectotympanic bones. Thus, while ectotympanic bone morphology is still useful in descriptions of primate phylogeny, it is more likely that it is a consequence of the shape of the cranium rather than an independent character. The ectotympanic bones of the two fossil species are shown to be abnormally short for catarrhine taxa, more similar to the platyrrhine condition. There is much more diversity in ectotympanic ii morphology than previously appreciated, particularly among lorisiforms. Some of that diversity is accounted for in the way in which the ectotympanic develops across taxa; lorisiforms and tarsiiformes are born with fully developed ectotympanic rings that lengthen to variable degrees likely due to relative cranial width. Dissertation Advisor: Valerie B. DeLeon, Johns Hopkins University and University of Florida Dissertation Committee: Jonathan M. G. Perry, Johns Hopkins University Mary T. Silcox, University of Toronto Lauren A. Gonzales, University of South Carolina iii Preface Acknowledgments I would like to thank my dissertation committee Drs. Valerie DeLeon, Jonathan Perry, Mary Silcox, and Lauren Gonzales. In particular, I want to thank my advisor Valerie who never gave up on me and never let me give up. She is the kind of scientist I have always wanted to be and I would never have made it through this dissertation without her. I also want to thank Darrin Lunde and Nicole Edmison for access to primates at the NMNH. I would like to thank the KUPRI, the Digital Morphology Museum (DMM) of the Primate Research Institute (PRI) in Kyoto for access to CT scans. Thank you to University of Pennsylvania Museum of Archaeology and Anthropology, the Open Research Scan Archive at Penn, and Drs. Janet Monge and P. Thomas Schoenemann specifically for access to human CT scans. I also thank Dr. Zabiulah Ali, Office of the Chief Medical Examiner Baltimore, for his help accessing juvenile human CT scans. I also want to express my gratitude to all scientists who make their data freely accessible. These databases are an important step towards increasing the scientific impact of and access to data worldwide. In particular I thank Dr. Fred Spoor and the Natural History Museum of Vienna for access to the scans of Pliopithecus vindobonensis; thank you to Alan Walker and Timothy Ryan for making their scans available on Morphosource and granting permissions. I also thank my cohort Kaya Zelazny for her scientific insights, unwavering friendship, and support. Thank you to the rest of my extended academic family, Christopher Ruff, Ken Rose, Dave Weishampel, Gabriel Bever, Adam Sylvester, and Siobhán Cooke for educating me and showing me what it means to be both an anatomist and anthropologist. iv Thank you to my family as well for their love and support: Mom, Starla, Devin, and Sharif. Thank you particularly to my husband, John, for always believing in me and pushing me to go after what I want even when things get hard. v Table of Contents 1.Introduction.................................................................................................................. 1 Literature Review ........................................................................................................ 3 Anatomy .................................................................................................................. 3 Evolutionary Origins of the Ectotympanic Bone ....................................................... 6 Phylogeny: Primate ................................................................................................10 Development of the Ectotympanic Tube .................................................................17 Functional Correlates .............................................................................................23 Structural Correlates...............................................................................................27 Conclusion .............................................................................................................30 2.Methods and Error Study ............................................................................................32 Error Study.................................................................................................................34 Scaling Factor ............................................................................................................37 3. Intraspecies Variation in the Catarrhine Ectotympanic Tube among Humans and Macaques ..................................................................................................................40 Introduction ................................................................................................................40 Hypotheses ................................................................................................................44 Materials and Methods ...............................................................................................45 Sample: Human ......................................................................................................45 Sample: Macaque ..................................................................................................45 Data Acquisition and Preparation ...........................................................................46 Data Analysis .........................................................................................................51 Results .......................................................................................................................52 Macaque Geometric Morphometrics .......................................................................52 Human Geometric Morphometrics ..........................................................................58 Intraspecific Variation in Ectotympanic Bone Length ..............................................62 Discussion .................................................................................................................67 Conclusion .................................................................................................................71 4. Geometric Morphometric Analysis of the Primate Ectotympanic Bone with Special Reference to the Fossil Record ..................................................................................73 Introduction ................................................................................................................73 Hypotheses ................................................................................................................77 Materials and Methods ...............................................................................................78 Data Acquisition and Preparation ...........................................................................78 vi Fossil reconstruction...............................................................................................81 Data Acquisition and Preparation ...........................................................................82 Data analysis ..........................................................................................................84 Results .......................................................................................................................84 3D Visualizations of the Ectotympanic Bone across Taxa ......................................85 Geometric Morphometric Analyses .........................................................................91 Middle Ear Correlates .............................................................................................95