Abstracts Category : Other

The phylogenetic position of Proconsul and catarrhine ancestral morphotypes

by Ashley Bales

There continues to be a lack of agreement concerning the precise phylogenetic placement of Proconsul despite the wealth of fossil material and the extensiveness of its study. The difficulty in resolving the phylogenetic status of this important and well represented Miocene catarrhine is a consequence of its apparent basal position relative to crown catarrhines. This position complicates the inference of character polarities. This dissertation tests three previously proposed hypotheses concerning the phylogenetic position of Proconsul: (1) Proconsul is a stem catarrhine; (2) Proconsul is a stem hominoid; and (3) Proconsul is a basal hominid, most closely related to extant great apes and humans. A phylogenetic analysis based on 719 characters drawn from the skull, forelimb, pelvis and foot, and sampling a diversity of extant anthropoid taxa, offers no compelling support for a hominoid clade that includes Proconsul. The radiation of crown catarrhines involved rapid evolutionary changes from the ancestral catarrhine morphotype, resulting in stem catarrhines appearing much more similar to each other, even where there are key synapomorphies linking them with crown clades. As a result, systematic analyses alone are insufficient to confidently support a single optimal phylogenetic hypothesis. Further exploration of the data, by combining inferred ancestral morphotypes with phenetic visualizations of character evolution, demonstrated that inclusion of Proconsul among Hominoidea or Hominidae pushed the ancestral catarrhine morphotype closer to these clades, respectively. Given a more comprehensive analysis of character evolution under each hypothesis, this dissertation supports the hypothesis that Proconsul is a stem catarrhine. In addition to helping clarify the long-running debate about the phylogenetic status of Proconsul, the results offer fresh insights into the early stages of hominoid evolution and demonstrate the importance of comprehensive phylogenetic analyses in helping to resolve the relationships of problematic stem taxa.