PhD Dissertations: Mana Dembo, 2016

Exploring morphological phylogenetics of fossil hominins

 

Abstract

A reliable phylogeny is critical for the study of hominin evolution, yet there remains considerable debate about the relationships among hominin species. Phylogenetic analyses conducted to date differ in various analytical aspects such as the fossil samples and characters used to infer their relationships. Given the importance of a phylogeny in the study of hominin evolution, four studies were designed to address some key issues in the phylogenetic analysis in palaeoanthropology. The first study investigated the effects of using small samples in standard phylogenetic analyses. The second study used ­tip-dated Bayesian analysis to test various phylogenetic hypotheses pertaining to three recent debates. The third study used the same method to evaluate the phylogenetic and temporal placement of a newly discovered species, Homo naledi, in the hominin phylogeny. The fourth study explored the impact of cranial modularity on the choice of characters used to reconstruct the phylogeny of the hominins.

Results suggest that small sample sizes can be problematic in phylogenetic analyses of extant hominoids. However, the choice of character coding methods may mitigate the effects of small samples. Bayesian phylogenetic analyses were conducted to evaluate various hypotheses from three recent debates and some hypotheses can be strongly refuted based on current evidence. The results of the analyses suggest that there is strong evidence that Homo naledi belongs to the clade of Homo and Australopithecus sediba, but its place within this clade is currently ambiguous. The results of this study place the fossil at approximately 1 Ma. Different cranial regions contain conflicting phylogenetic signals, but none of the regions particularly stand out as having more homoplastic characters. The hominin phylogeny is necessary to study hominin evolution, and as such, it is important to improve the methods used to reconstruct the evolutionary relationships of hominins. The use of Bayesian phylogenetic methods is promising for palaeoanthropology as it can narrow the scope of debate surrounding phylogenetic hypotheses. It allows us to highlight where ambiguities in the data and the model exist and demonstrate the limit of the interpretation of the current fossil evidence.