A comparative analysis of the wrist and ankle morphology of hominoids and lorisids, with implications for the evolution of hominoid locomotion

Abstract

There has been considerable debate concerning the adaptive significance of hominoid postcranial anatomy. One of the hypotheses promoted is that the early hominoids were adapted to a loris-like deliberate quadrupedalism. The aim of the analysis reported here is to test this hypothesis by examining features of the wrist and ankle anatomy of lorisids and hominoids that pertain to increased joint mobility, in a comparative context with other arboreal quadrupeds. These characters are then compared with the Proconsulidae from the early Miocene to discern any similarities between these taxa and the lorisids and/or hominoids. Fourteen characters were examined, related to the ulnocarpal and radioulnar articulations, and the talocrural, subtalar and midtarsal joints, across four lorisid and four hominoid genera, and a selection of primates from the other major groups. Original measurements were taken for two hundred and twenty-nine neontological specimens in total, from fourteen genera. Indices were devised and compared by statistical analysis. The results suggest that lorisids and hominoids are similar in some of the characters examined, but differ in others. The proconsul ids show varying degrees of similarity across the features, to the hominoids and lorisids. The results support a hypothesis that an early hominoid ancestor did indeed have similar functional adaptations to those of extant lorisids, but not across the whole suite of characters examined. It is therefore reasonable to assume that the ancestral hominoid locomotor pattern showed resemblances to that of the extant lorisids, but was not identical.