Anthropology Department, University College London
Saturday Morning, Forum Suite
Hominoid primates share a number shoulder morphologies associated with arms used for overhead movements. Considerable debate exists, however, over whether these features are a product of shared ancestry or parallel evolution. Humeral torsion (i.e., rotation of the humeral head on the shaft), has received particular attention within this debate because of its potential in diagnosing locomotion in fossil primates.
Developmental data has been suggested to be informative in perceiving homology and homoplasy in a paleoanthropological context, although opinions are still divided on the value of ontogenetic analyses.
We investigate whether within-species ontogenetic approaches are aligned with between-species comparative approaches in estimating shared derivation of humeral torsion in African apes. We investigate 1) ontogenetic growth patterns by applying Gompertz curves to within-species population-level data of humeral torsion, and we investigate 2) rates of change of humeral torsion across individual branches of a phylogeny of 25 primate species.
Both the within-species and the between-species analyses point towards humeral torsion being a shared-derived trait among African apes and humans: 1) the growth curves of African apes and humans are almost identical in shape and parameters, indicating that humeral torsion arises through homologous developmental processes, which suggests that humeral torsion is a shared derived character ; 2) the macroevolutionary analysis indicates a substantial increase in humeral torsion in the ancestral branch of African apes similarly suggesting shared derivation of humeral torsion.
These results show that ontogenetic growth patterns provide valuable information when exploring issues of homology versus homoplasy in primate hard tissue anatomy.