THE COMPARATIVE ANATOMY OF THE HOMINOID CRANIAL BASE by Michael Christopher Dean Thesis submitted for the degree of Doctor of Philosophy. Department of Anatom y and Biology as Applied to Medicine, The Middlesex Hospital Medical School, Universit y of London. October 1982 2. ABSTRACT This thesis uses metrical data and morphological observations to describe the comparative anatomy of the cranial base region in extant adult hominoids. The changes that occur during growth in this region have also been studied in samples of juvenile hominoids, and cross-sectional growth data for the same variables measured in the adult metrical study have been recorded. Detailed metrical and morphological observations were also made on a series of fossil hominid crania dating from the Plio- Pleistocene. The results of the two comparative studies of the cranial base region in extant hominoids were then used to assess the significance of the differences noted in the cranial base region of the fossil hominids from sites in South and East Africa. The results of the adult metrical study; and the series of soft tissue dissections, demonstrate that there are fundamental differences in the comparative anatomy of the modern human and pongid cranial bases. The results of the comparative growth study indicate that these differences are probably not the result of an overall acceleration, or retardation, in growth rates of the component bones of the human cranial base, but more likely due to a combination of increases and decreases in growth rates occurring in individual bones, as well as to differences in morphology already manifest soon after birth. The results of the study of fossil hominid specimens indicate that the 'gracile' australopithecine fossils from South Africa have a cranial base pattern similar to that of the extant pongid samples, but that the 'robust' australopithecine fossils, and those fossils attributed to early Homo have a cranial base pattern more similar to the modern omo sapiens samp1. These differences in basicranial anatomy among the fossil hominid sample provide a useful tool to assess the taxonomic status of several 3. hominid fossil specimens which are still of uncertain taxonomic designation. The comparative studies of the hominoid cranial base also provide a framework which enables features of this region to be used in phylogenetic analysis. 1- ACKNOWLEDGMENTS. I would first like to thank my Supervisor, Dr. Bernard Wood, for his wise and patient supervision and for his kindness and friendship towards me during the last five years. Much of the work in this thesis was carried out in the Department of Anatomy, The Middlesex Hospital Medical School, Cleveland Street, London, W.C. 1 and I would like to thank Professor P.H. Silver for his generosity in making facilities available to me, even after the termination of my studentship. I would also like to thank Mr. A. Rote and Mr. S, Karby for their help with the preparation of many wet specimens and Mr. C. Sym for his invaluable help with the photography. I am also very grateful to Dr. Michae 1 Clarke for his generous help with computing problems. During the past five years many people have given me practical help and encouragement and I would like especially to thank the following: Ms. S. Abbott, Professor A. Boyde, Professor G.H. DeBoulay, Mr. T. Bryant, Mr. M. Catchpole, Mrs. M . J. Harvey, Dr. P . N. Holmes and Mr. A. Hughes. I would also especially like to thank the following trustees of many museums for their assistance and stimulating interest in my work and for allowing me access to valuable collections of extant primate and fossil material: Dr. C.K. Brain and Dr. E.S. Vrba, Professor P.V. Tobias, R.E.F. Leakey and M.D. Leakey, Mrs. P. Napier and C. Powell-Cotton, L . R. Barton and M. Harman. I am also extremely grateful to Elizabeth Marshall and Janet Marx for typing the figures and manuscript. This thesis was supported by an N.E.R.C. Research Studentship. 5-. TABLE of CONTENTS. Page. i. Abstract 2 ii. Acknowledgments 4 in. Table of Contents 5 iv. List of Tables 7 v. List of Figures 8 vi. List of Plates 10 vii. Introduction 11 PART I: LITERATURE REVIEW Chapter 1. The basicranium of adult hominoids and related studies. 14 Chapter 2. Growth changes in the cranial base of hominoids. 31 Chapter 3. The soft tissue anatomy associated with the hominoid basicranium. 52 Chapter 4. The cranial base of fossil hominids. 72 PART II: MATERIALS and METHODS Chapter 5. Materials: Comparative sample and fossil hominid crania 8 Chapter 6. Methods: 96 i. Apparatus 97 ii. Definition of anatomical landmarks and definition of measurements made directly from specimens 1OC iii. Test of accuracy of measurement techniques 105 iv. Radiographic techniques 106 v. Definition of anatomical landmarks and measurements made from radiographs of the pongid specimens 112 vi. The accuracy of the tedinique used for correcting measurement magnification 116 vii. Asymmetry of the cranial base 118 viii. Dissection of wet comparative ponid specimens 120 ix. The method of reconstructing the cranial base of certain fossil hominid crania 120 6. Page x. The method of studying muscle markings on the cranial base of certain fossil hominids 121 xi. Statistical and analytical methods 122 xii. Summary of the materials and measurements used in each of the four separate studies of this thesis 123 Chapter 7. The method of ageing individual skulls. 12 PART III: RESULTS Chapter 8. Results of the adult metrical study. 137 Chapter 9 Results of the study of postnatal growth changes in the cranial base of hominoids. 143 Chapter 10. Results of the dissection study of the cranial base region in Gorilla gorilla, Pan troglodytes and Pongo pygmaeus. 196 Chapter 11. Results of the metrical study of the fossil hominid crania and of the study of muscle markings on the cranial base of certain fossil hominids. 219 PART IV: DISCUSSION Chapter 12. Discussion 238 Chapter 13. Conclusions 270 !'ART V: REFERENCES: Literature cited 284 PART VI: APPENDIX 7. LIST of TABLES. Page. Table 1. Summary of adult skulls used in this study 93 Table 2. Summary of juvenile skulls (pooled sexes) used in this study 94 Table 3. Originals and casts of fossil hominid crania and skulls used in this study 95 Table 4. Measurement error, expressed as a percentage of the sample range, for ten measurements repeated five times on specimens of Homo and Pan 105 Table 5. Results of measurements made on the left and right hand sides of 99 skulls to test for the degree of asymmetry of the cranial base 119 Table 6. Showing the numbers of individuals in Gorilla, Pan and Pongo, in which the developmental stages A - K are coincident 129 Table 7. Parameters and measurements of adult comparative groups 138-140 Table 8. Parameters and data of comparative groups presented in growth study 144-146 Table 9. Cranial base data for hominid fossils 220 8. LIST of FIGURES. Page. 1. Longitudinal and vertical sections of the skulls of a Beaver, aLemurandaBaboon (from Huxley 1863, p.149). 16 2. Sections of orthognathous and prognathous skulls (from Huxley 1863, p.151). 18 3. Landmarks and angles used in previous studies of the cranial base. 38 4. Diagram of the human cranial base with the areas associated with muscle attachments outlined. 65 5. Landmarks seen in norma frontalis in Homo sapiens and Pongo pygmaeus. 102 6. Landmarks seen in norma basilaris in Homo sapiens and Gorilla gorilla. 103 7. Diagram illustrating the theoretical magnification of an object 100 mm long and 50 mm away from a point X-ray source. 108 8. Diagram of the midsagittal section of a specimen of Pan troglodytes to illustrate the radiographic landmarks used in thirt of the study. 113 9. Skull base diagram of Homo sapiens with landmarks and angular measurements. 114 10. Radiographic appearance of developmental stages of teeth. 128 11. Calcification times in years for the developing human and pongid dentitions. 131 12. Chart of the developing pongid dentition. 132 13. Plot of jaw length in the gorilla against relative dental age. 133 14. Skull base diagrams of Homo sapiens, Gorilla gorilla, Pan troglodytes and Pongo pygmaeus. 141 9. Page. 15 - 42. Plots of measurements made on the cranial base against relative dental age for specimens of Homo, Pan, Pongo and Gorilla. 148-192 43. Skull base diagrams of fossils attributed to Australopithecus africanus with Homo and Gorilla for comparison. 221 44. Skull base diagrams of fossils attributed to Australopithecus (Paranthropus) robustus with Homo and Gorilla for comparison. 222 45. Skull base diagrams of fossils attributed to Homo erectus with Homo and Gorilla for comparison. 223 46. Skull base diagrams of PLio-Pleistocene hominid crania from East Africa with Homo and Gorilla for comparison. 224 47. Skull base diagrams of individual Plio-Pleistocene hominid crania from South Africa with Homo and Gorilla for comparison. 225 10. LIST of PLATES. Page Plate 1. Perspex craniostat and portable 'Atomscope' X-ray machine. 99 - Plate 2. Perspex craniostat with skulls positioned in A; norma basilaris, B; norma lateralis and C; norma frontalis. 111 Plates 3 and 4. Plates of dissection of the cranial base region of Pongo pygmaeus. 198 Plates S and 6. Plates of dissection of the cranial base region of Pan troglodytes (specimen 1). 209 Plates 7 and 8. Plates of dissection of the cranial base region of Pan troglodytes (specimen 2). 212 Plate 9. Plate of dissection of the cranial base region of Gorilla gorilla (specimen 2). 215 Plate 10. Outlines of muscle markings on the cranial base of MLD 37/38, Sts 5, KNM-ER 406, OH 5 and SK 47.