THE INFLUENCE OF POSTURE AND BRAIN SIZE ON FORAMEN MAGNUM POSITION IN BATS A thesis submitted to Kent State University in partial fulfillment of the requirements for the degree of Master of Arts by Aidan Alifair Ruth May 2010 Thesis written by Aidan Alifair Ruth B.A., The Ohio State University, USA 2008 Approved by C. Owen Lovejoy___________________________ , Advisor Richard S. Meindl__________________________ , Chair, Department of Anthropology John R. D. Stalvey___________________________, Dean, College of Arts and Sciences ii TABLE OF CONTENTS LIST OF FIGURES ......................................................................................................... V LIST OF TABLES .......................................................................................................... VI ACKNOWLEDGEMENTS ............................................................................................. VII ABSTRACT………………………………………………………………………………………………………………… IX CHAPTER 1 INTRODUCTION ........................................................................................ 1 1.1 Anatomy and Development of the Basicranium ....................................................... 1 1.2 Postural Hypotheses.................................................................................................. 2 1.3 Facial Orientation Hypotheses .................................................................................. 3 1.4 Neural Hypotheses .................................................................................................... 4 1.5 Neural Reorganization ............................................................................................... 5 1.6 An Integrated Hypothesis .......................................................................................... 6 1.7 The Chiroptera ........................................................................................................... 7 CHAPTER 2 HYPOTHESES .......................................................................................... 15 CHAPTER 3 MATERIALS AND METHODS .................................................................... 17 3.1 Data acquisition ....................................................................................................... 17 3.2 Measurements ........................................................................................................ 18 CHAPTER 4 RESULTS ................................................................................................. 20 4.1 Principal Components Analysis ............................................................................... 20 4.2 Correlation Analyses................................................................................................ 21 4.3 Analysis of Covariance ............................................................................................. 21 CHAPTER 5 CONCLUSIONS ........................................................................................ 27 5.1 Foramen magnum position is influenced by neocortex size, but not brain size or posture .............................................................................................................................. 27 5.2 Neural Reorganization is consistent with the hominid fossil record ...................... 30 APPENDIX A ............................................................................................................. 34 CITED LITERATURE .................................................................................................... 36 iv LIST OF FIGURES Figure 1.1. Weidenreich’s Postural Hypothesis……………….……………………………………………10 Figure 1.2. Lateral Radiographs of Cat, Rat, and Rabbit………………………………………………..11 Figure 1.3. Dabelow’s Facial Orientation Hypothesis…………………………………………………….12 Figure 1.4. Biegert’s Hypothesis for the anterior position of the foramen magnum in humans…………………………………………………………………………………………………………….13 Figure 1.5. Basal view of Saimiri oerstedii and Alouatta seniculus…………………………………14 Figure 3.1. Measurements used in analysis…………………………………………………………………..19 Figure 4.1. Results of Principal Components Analysis……………………………………………………22 Figure 4.2. Results of Analysis of Covariance: Encephalization Quotient……………………..23 Figure 4.3. Results of Analysis of Covariance: Neocortical Quotient……………………………24 v LIST OF TABLES Table 4.1 Component Loadings. ....................................................................................23 vi ACKNOWLEDGEMENTS My gratitude for the help of many individuals during the completion of this thesis can be described using two principal components. The first component may be described as the “Scientific Support” component. Individuals who load heavily on this component include my advisor, Owen Lovejoy, whose prolific expertise in biological anthropology is truly inspiring; Mary Ann Raghanti, whose knowledge in brain biology is staggering; and Richard Meindl, whose resemblance to an encyclopedia is uncanny. Also loading heavily on this component are Suzanne McClaren at the Carnegie Museum of Natural History Mammals Section, who allowed me access to her beautifully maintained collections of bats and helped me navigate the city of Pittsburgh, and Andy Jones at the Cleveland Museum of Natural History, who allowed me access not only to his collection of bird skeletons, but also to a sample of birds to dissect. The second component of my gratitude may be described as the “Moral Support” component. A certain degree of colinearity exists between the two components: Dr. Lovejoy loads heavily on this component, for making me feel proud of my work. Dr. Raghanti’s “open door” policy has helped me immeasurably, as has her reminder that there is no crying in science. Dr. Meindl’s reassuring demeanor has helped me remain (relatively) calm through many statistical and academic emergencies. vii My parents, Steve Ruth and Carol Goodnight, have been especially supportive during the past two years. Finally, my “Monkey Family,” composed of the other grad students in the anthropology department, has contributed many giggles, long talks, and cups of coffee to this component as well. Aidan Ruth 19 March 2010, Kent, Ohio viii ABSTRACT An anterior position of the foramen magnum is often cited as a correlate of bipedal posture in hominids. Other investigators (Biegert 1963) have suggested that it more accurately reflects increased encephalization. The present study examines this problem in bats, which most commonly employ an inverted but orthograde posture during rest but all which participate in active flight. The position of the foramen magnum was evaluated using Bolk’s Basal Index (1909). A mean Basal Index was obtained for ten species of bat belonging to the pteropodidae subfamily, and twenty belonging to the Phyllostomidae subfamily. Measures of brain volume and were obtained from Baron (1996) and used to create two different indices of neural organization: An Encephalization Quotient (Brian volume/Body volume) and Neocortical Quotient (Neocortex volume/Telencephalon volume). A strong negative correlation was found between Neocortical Quotient and Basal Index in both Pteropodidae (r= -.717) and Phyllostomidae (r= -.566), as predicted by Biegert’s hypothesis. A linear model shows an interaction between subfamily and Neocortical quotient (r2 = .828). Since substantial variation in locomotor pattern and/or posture does not obtain within this group of bats, this confounding variable can be excluded. These data provide strong evidence that the position of the foramen magnum may be used as a potential indicator of neural reorganization (in particular, expansion of ix the neocortex), but not as an indicator of posture. x CHAPTER 1 Introduction An anterior position of the foramen magnum is often cited as an anatomical correlate of bipedal posture in hominids. Because bipedality is considered to be one of the earliest “hallmarks” of the hominidae, it is tempting to infer its presence whenever possible. However, an anterior foramen magnum may not reflect an adaptation to upright walking, but instead increased neocortical volume. This study seeks to explore this issue using data from the order Chiroptera. Chiroptera share many adaptations with primates, especially orbital frontation and a trend toward increased brain size and reorganization. Furthermore, the Chiroptera have abandoned quadrupedal locomotion for flight and have adopted an inverted but orthograde posture when at rest. 1.1 Anatomy and Development of the Basicranium The skull is a highly integrated structure. It is traditionally divided into three units based on embryonic origins, development, and function: The face, the neurocranium, and the basicranium (Hanken and Hall 1993). The face and neurocranium develop primarily by intramembranous ossification, and their shape is therefore dependent on the soft tissue structures around which they develop (e.g., the brain). The basicranium develops through endochondral ossification, during which a set of cartilaginous precursors is replaced by bone. Growth occurs at synchondroses which resemble the 1 2 growth plates of typical long bones (Hanken and Hall 1993). The foramen magnum transmits the medulla oblongata and is located in the occipital. The occipital articulates with the sphenoid at the spheno-occipital synchondrosis, and with the right and left temporals at the lambdoid suture. Deposition of bone occurs along the borders of these synchondroses throughout development so that the skull changes shape by means of differential growth at these sites throughout