The extent of homoplasy in the trunk and forelimb of the hominoidea

Abstract

For the last century, palaeoprimatologists have questioned whether extant hominoids acquired their hunk and forelimb adaptations (previously interpreted as correlated with forelimb suspension) from a common ancestor, or developed them independently. Various workers have proposed that (1) the adaptations are hominoid synapomorphies; (2) hylobatids acquired these traits independently of hominids; (3) pongines and hylobatids evolved these features independently of each other and the African apes/humans; (4) the adaptations are independently derived in all homuioid genera. To test between these alternatives, nine characters from the trunk and forelimb are used to determine the evolution of character states in extant and Miocene hominoids. Metric traits from ten extant anthropoid and nine fossil catarrhine genera are used in computer based analyses to reconstruct the ancesfral conditions of these traits for a given cladogram. Ancestral morphotypes are compared with conditions exhibited in terminal taxa to identify synapomorphy/homoplasy. Results suggest that five of the nine characters examined are hominoid synapomorphies. Of the remaining traits, one is shared derived for hominids, one is a synapomorphy of the African ape/human clade, one is not diagnostic for apes at all, and one reflects absolute differences in body size between taxa. Four traits exhibit homoplasy, in the form of convergence or reversal. None of these traits, however, show homoplasy between two or more hominoid taxa. Therefore, it is unlikely that hylobatids, pongines or African apes/humans evolved these traits independently of each other. Three main conclusions can be drawn from this study: (1) some of the characteristics previously interpreted as synapomorphies for extant and stem hominoids are not in fact shared derived for this clade; (2) there is no homoplasybetween extant hominoid genera in the features examined; and, (3) the association of these traits with forelimb suspensory locomotion is unlikely.