The significance of early hominid cranial variability

Abstract

The aims of this thesis are: 1. To examine patterns of morphological variation in the crania of extant species {Pan, Gorilla, Pongo, and H. sapiens) to determine if any common pattern of primate sexual dimorphism exists which could be used in the assessment of fossil hominid sexual dimorphism; 2. To examine patterns of between species variability among the crania of the above extant species to determine if characters exist which could be useful as taxonomic indicators, especially of specific distinctiveness in fossil Hominidae; and 3. To assess the validity of using traits which are dimorphic and/ or variable within species as taxonomic indicators in systematic analyses. This thesis entails an analysis of inter- and intra-specific diversity among the early hominids based on models derived from samples of modern H. sapiens and pongids. Metrical cranial characters were surveyed in order to assess the implications of their variability within the available early hominid sample {A. afarensis, A. africanus, A. robustus, A. boisei, H. habilis, and H. erectus) using univariate, multi variate, and cladistic analytical techniques. The univariate analysis found no common pattern of primate sexual dimorphism but it did identify characters of low sexual dimorphism and low variability common to all the extant hominoids. These were used to test the homogeneity of the fossil groups and indicated the possible heterogeneity of H. erectus, H. habilis, A. afarensis, and A. boisei. The remaining characters revealed an apparent trend among the hominids (fossil and modern) of dimorphic regions of the skull including the areas of nuchal and temporal muscle attachment, kyphosis of the basicrania, width of the palate, mandible, and base, and facial prognathism. The multivariate analyses used the patterns of variability and dimorphism known from the modern comparators to assess sex, degrees of sexual dimorphism, and homo geneity of the fossil samples. These analyses revealed the possible heterogeneity of H. erectus and A. afarensis, the sex of some individual specimens, and some interesting contrasts in the patterns of sexual dimorphism between the fossil and modern species. They also isolated KNM-ER 1805 as having unique basicranial proportions. Two different types of characters were used in cladistic analyses to determine which type produced the most parsimonious trees and the implications of their use for future cladistic analyses. The results show that non-variable, non-dimorphic traits generally produce more parsimonious trees than variable, dimorphic ones, thus demonstrating the importance of assessing within- and between-group variability of characters prior to cladistic analyses. The method of coding the data prior to the cladistic analysis was tested for its objectivity. The analyses showed that the constant used to code the data into discrete character states had a substantial effect upon the resultant trees. This study has demonstrated that characters have different properties due to the amount they vary or are dimorphic within groups and that utilising these characters for different purposes has the potential to enhance future systematic/ phyletic studies. [brace not closed]