One of the most long-standing problems in primate evolution is the nature of the relationships of Middle to Late Miocene (13-8 million years old) apes to each other, to living great apes, and to humans. Scientists have formulated many different hypotheses about hominoid (ape) relationships, but the application of different methods and the use of different skeletal features have raised the question of whether the observed results are an accurate representation of relationships or whether they are simply an artifact of the methods used and traits chosen. Current hypotheses about the evolutionary relationships of early representatives of the human lineage rely largely on comparative analyses of the highly specialized features in living African apes and modern humans. This project will offer an important new perspective on hominoid relationships by incorporating the greater range of diversity and less specialized morphologies seen in Miocene apes in order to clarify the sequence in which features evolved. This research involves a comprehensive analysis of 123 cranial and postcranial features, from 17 living primates, which have been previously used to infer evolutionary relationships among Miocene apes. These traits will be compared individually, by anatomical system and holistically, to independent (i.e., molecular) measures of evolutionary relationships. Skeletal features will first be quantified by linear measurements, and then analyzed individually in permutation tests to assess the statistical significance of the information they contain about evolutionary relationships. Parsimony analyses will then be performed on these living species, as well as four later Miocene apes, using those features that are found to have the highest information content in resolving relationships. The results should indicate how much the choice of different methods and traits is influencing our perception of Miocene hominoid evolution, and thus provide a firmer foundation for clarifying the evolutionary relationships of both Miocene apes and early fossil humans.
This project will provide new insights into the utility of different methods and skeletal traits for inferring evolutionary relationships, and a rigorous test of current hypotheses about evolutionary relationships in Middle to Late Miocene apes. The study of Miocene apes is critical because they represent close relatives of humans, and some later Miocene species are likely to prove to be early members of the lineage leading to modern humans. As a consequence, a better understanding of the sequence in which traits evolved in Miocene apes and clarification of their relationships to living apes will have major implications for understanding human evolution.
