Serdoz, D; (2006) An assessment of the utility of nerve- and vessel-related cranial characters for reconstructing primate phylogeny. Doctoral thesis , UCL (University College London).

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Abstract

Recent analyses have suggested that standard craniodental characters may be misleading regarding primate phylogenetic relationships. This has important implications for the study of human evolution because such characters dominate the datasets used to reconstruct the phylogenetic history of fossil primates. This project was designed to identify characters that will allow fossil primate relationships to be reconstructed more confidently. It is based on the finding that hominoid soft-tissue characters yield a phylogeny consistent with the strongly supported molecular phylogeny for these primates. If soft-tissue characters are phylogenetically informative then osteological characters associated with soft tissue may also be phylogenetically informative. Information regarding the size, number, shape and position of cranial foramina and canals was collected on a sample of 30 Gorilla gorilla, 20 Pan paniscus, 30 Pan troglodytes, 48 Homo sapiens, 31 Pongo pygmaeus, 59 Hylobates plus three outgroups (Cercopithecus, Colobus and Papio). This information was coded into 112 characters using four different coding methods (Divergence coding, Segment coding, Baum's coding and Binary coding) and then subjected to parsimony and bootstrap analyses. The resulting phylogenies were compared to the well supported and widely accepted hominoid molecular phylogeny. Agreement between the morphology-based phylogenies and the consensus molecular tree would support the hypothesis that cranial characters related to nerves and vessels produce reliable phylogenies for the hominoids. Seven of the 16 parsimony tests produced cladograms compatible with the consensus molecular phylogeny. In contrast, the bootstrap tests produced clades consistent with the molecular cladogram in all but one case. Thus, the parsimony tests only moderately supported the hypothesis while bootstrap tests strongly supported the hypothesis. Furthermore, the dataset composed of characters related to nerves and vessels performed significantly better than a dataset composed of standard craniometric variables in recovering the molecular relationships of the hominoids. Overall, these results suggest that primate foramina and canals may be a better focus for phylogenetic studies than standard craniodental characters. It also emerged that the results of the parsimony analyses varied depending on the coding procedure adopted and on the composition of the outgroup. Divergence coding stood out as the most rigorous method and outperformed all other methods. In terms of outgroup choice, this study supports Colless (1985) suggestion that a number of taxa, or groups of taxa, should be used as outgroups in a phylogenetic analysis and then a consensus of the results should be drawn. Interestingly, bootstrap analyses seemed to be less affected by these factors and produced consensus cladograms that were consistent with each other and with the molecular tree. Lastly, the effects of sexual dimorphism and non-phylogenetic character correlations were also investigated. The results indicated that both factors may have an effect on the outcome of phylogenetic analyses. These findings are discussed in the context of phylogenetic studies of fossil hominin material.

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