A morphometric study of cranial shape in the Hominoidea
This study investigates the applicability of a number of traditional and newer methods of morphological description to the problem of defining hominoid cranial form. The aim has been to produce an objective assessment of the relative merits of the methods from both a practical and theoretical perspective. The thesis is presented in three parts. In the first, several approaches which offer potential in the description of cranial morphology are reviewed and the phenetic relationships of the crania of extant hominoids are examined using data obtained by a variety of new (shape factors, least squares, and Fourier analysis) and more traditional (dimensions, angles and indices) approaches to morphological description. The analysis concentrates on a comparison of the resulting patterns of group dispositions and on an examination of the ability of the various approaches to allow an accurate determination of the affinities of crania of unknown provenance. The results indicate that there is little difference in the patterns of phcnetic relationships obtained although it appears that the analyses based upon linear and angular measurements and Fourier coefficients provide the widest separation between the groups. The second study employs linear and angular measurements and Fourier coefficients in an examination of within-group cranial variability. In general the results lead to similar conclusions about the patterns of sexual dimorphism in extant hominoid crania and the influence of size on cranial morphology. The analyses of Fourier data differ from those of linear and angular measurements, however, in that purely size related variation is given a smaller weighting relative to morphological variation attributable to other sources. In the third part the fossil record relating to the evolution of Homo is reviewed. The third study employs these same two approaches to morphological description in a study of the patterns of cranial variation between certain fossil hominids. By contrast with the first study the pattern of phenetic relationships between OTUs appears to be considerably influenced by the choice of measurement method although there is a common underlying pattern of group dispositions. The reasons for these differences are considered in the light of the results of multivariate morphometric studies of cranial form undertaken by other workers. From these studies it is concluded that: a) the results obtained by studies employing landmark dependent and data with reduced landmark dependence may differ to some degreea nd that this difference is principally related to differences in the ways in which the various anatomical regions influence the measurements, b) the choice of method for craniometric problems should be determined with due regard for the task at hand, c) the investigator should be aware of the potential pitfalls and advantages of each method in furnishing answers to specific questions, d) the investigator should be aware of the fact that the use of different morphological descriptions may give rise to different results.