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Quantitative Assessments of Avian Endocasts As Tools for Inferring Neuroanatomical Quantitative Assessments of Avian Endocasts as Tools for Inferring Neuroanatomical Traits and Potential Functional Capabilities A dissertation presented to the faculty of the College of Arts and Sciences of Ohio University In partial fulfillment of the requirements for the degree Doctor of Philosophy Catherine M. Early May 2019 © 2019 Catherine M. Early. All Rights Reserved. 2 This dissertation titled Quantitative Assessments of Avian Endocasts as Tools for Inferring Neuroanatomical Traits and Potential Functional Capabilities by CATHERINE M. EARLY has been approved for the Department of Biological Sciences and the College of Arts and Sciences by Lawrence M. Witmer Professor of Biomedical Sciences Joseph Shields Interim Dean, College of Arts and Sciences 3 ABSTRACT EARLY, CATHERINE M, Ph.D., May 2019, Biological Sciences Quantitative Assessments of Avian Endocasts as Tools for Inferring Neuroanatomical Traits and Potential Functional Capabilities Director of Dissertation: Lawrence M. Witmer The brains of different species birds are influenced by the functional demands of their respective lifestyles, with the relative size of a given structure often correlating with the emphasis placed on the information it processes. The brain endocasts of birds (or simply “endocasts”) are relatively faithful representatives of the external shape and size of the brain, and they are the most direct source of information about the neuroanatomy of extinct birds. Other traits in the skulls of birds, such as nerve foramina and canals, may also provide information about neuroanatomy in the absence of soft tissue. This dissertation explores the utility of endocasts and other potential osteological correlates of neural tissues for making inferences about neuroanatomy and potential functional capabilities of birds. For the most part, these chapters are based on endocasts generated from microCT scans of bird specimens from museum collections. Various aspects of endocast morphology, such as the surface areas of brain endocast structures like the optic lobe and Wulst or the volume of the trigeminal apparatus, were measured and analyzed. First, a comparison of the endocast of an extinct giant moa, Dinornis robustus, with those of other palaeognaths revealed apomorphic reductions of the optic lobe and floccular lobe in this extinct bird. The roles that the brain structures underlying these 4 endocast structures play in stabilizing the image on the retina suggests that their reduction could have impacted this aspect of vision in D. robustus. Next, the relationship between the optic tectum and hyperpallium, two brain structures involved in vision, and the optic lobe and Wulst, the overlying endocast structures, was quantified in a sample of extant birds. A strong, significant relationship was found between each endocast and brain structure, indicating that the size of these endocast structures can be used to infer the size of the brain structures. As the size of these brain structures has been shown previously to correlate with visual specializations or degree of reliance on visual information, these endocast structures can also be used to infer functional capabilities in a general sense. This strong relationship between endocast and brain structures in extant birds was used to predict brain-structure volumes from the endocast-structure surface areas of a selection of extinct birds, yielding optic tectum volumes of seven extinct birds and hyperpallium volumes of five extinct birds. Novel quantitative methods were used to test if any of the extinct birds had smaller brain-structure volumes or endocast-structure surface areas than would be predicted by the allometric trends present in the rest of the birds in the sample. These tests indicated that almost all of the extinct birds fell within the range of variation of brain-structure volumes and endocast-structure surface areas seen in extant birds, but that D. robustus had a significantly smaller optic tectum and optic lobe. Finally, potential osteological correlates for the trigeminal system, such as neurovascular foramina on the bill, trigeminal apparatus volume, and Wulst position, were tested as indicators of trigeminally-mediated tactile feeding behaviors. The number 5 of foramina on the bill did not correlate with touch-based feeding behaviors, but trigeminal apparatus volume and Wulst position did, indicating that these two less- explored traits are better bases for inferences about tactile sensitivity of the bills of birds. Together, the results of this dissertation demonstrate the strength with which neuroanatomy and functional capabilities can be inferred in extant and extinct birds from their endocasts. This dissertation provides quantifiable osteological correlates for some neuroanatomical traits and their potential functional implications that should be utilized in future studies on the visual and trigeminal systems of extinct birds. 6 DEDICATION This work is dedicated to Bob-Bob, Pop-Pop, and the rest of my family, whose love (to the moon and back) and support made this possible. 7 ACKNOWLEDGMENTS I offer heartfelt thanks to my advisor, Dr. Lawrence Witmer, for giving me the opportunity to grow professionally and personally in his lab and for the many hours he spent working with me on this dissertation. I thank my committee for valuable feedback on this dissertation, and the individual members for their special contributions: Dr. Shawn Kuchta for brainstorming statistical analyses, Dr. Patrick O’Connor for pushing me to always think more deeply about neuroanatomy, and Dr. Alycia Stigall for serving as a role model for me as a fellow woman in paleontology. For the first chapter, thanks are due to the Field Museum of Natural History for loaning the Dinornis robustus specimen to my advisor and to R. P. Scofield for providing valuable information on the history of the specimen. Dr. Amy Balanoff, Dr. Julia Clarke, and Chris Torres contributed particularly helpful discussion during the development of that chapter. The second and third chapters were vastly improved by help with phylogenetic methods and statistical analyses from Dr. Ryan Felice and Dr. Haley O’Brien. Thanks to Dr. Federico “Dino” Degrange, Shelby Jordan, Dr. Daniel Ksepka, Dr. Angela Milner, Ryan Ridgely, Cheyenne Romick, Meg Wakui, and other WitmerLab members and collaborators for contributing CT scans or endocast segmentation of extant and extinct birds used in the second and third chapters. Dr. Andrew Iwaniuk provided access to histological sections of avian brains and deeply influential discussion for those two chapters. The fourth chapter was made possible by a National Science Foundation (NSF) Graduate Research Internship Program (GRIP) award to me and by Dr. Helen James, my research host and mentor during my GRIP at the Smithsonian National 8 Museum of Natural History. Discussions with Dr. Martina Crole and Dr. Susan Cunningham greatly improved the development of that chapter. All chapters were made possible by collections staff at the American Museum of Natural History, the Field Museum of Natural History, the Smithsonian National Museum of Natural History, and the Yale Peabody Museum of Natural History who granted access to specimens, and by the friends who hosted me during collections visits. Special thanks to Dr. Daniel Ksepka for introducing me to this field and for continuing to be a dedicated mentor and friend. I thank Dr. Jane Balbo and Dr. Michelle Pride for their devoted and compassionate healthcare, Christina Nasuti Phillips and Andrea Reany for providing important outside perspectives, and Drew Harper for years of supportive partnership. Many members of the Ohio Center for Ecology and Evolutionary Studies provided fruitful discussion and support, including Dr. Jason Bourke, Don Cerio, Jasmine Croghan, Wren Edwards, Maggie Hantak, Melissa Liotta, Dr. Ashley Morhardt, JP Nassif, Emily Naylor, Dr. Wm. Ruger Porter, Karie Whitman, and Dr. Susan Williams. This work was funded in part by National Science Foundation grants IBN-0343744, IOB-0517257, IOS-1050154, and IOS-1456503 to my advisor. Additional funding to me from the Ohio University (OU) Graduate Student Senate and Graduate College, OU Office of the Vice President for Research and Creative Activity, and the Frank M. Chapman Memorial Fund of the American Museum of Natural History (AMNH) supported this research. This dissertation is a result of work supported by the National Science Foundation Graduate Research Fellowship Program under Grants No. DGE 1060934 and 1645419 to me. 9 TABLE OF CONTENTS Page Abstract ............................................................................................................................... 3 Dedication ........................................................................................................................... 6 Acknowledgments............................................................................................................... 7 List of Tables .................................................................................................................... 12 List of Figures ................................................................................................................... 13 Dissertation Overview ...................................................................................................... 16 Chapter 1: The Neuroanatomy of the Giant Moa Dinornis robustus (Aves: Dinornithiformes): A Comparison to Other Palaeognaths and Consideration of Behavioral Implications ...................................................................................................
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