A closer look at the postcranial skeleton of Omo I from the Kibish Formation, Ethiopia: points of divergence from recent humans

Previous studies have described the postcranial skeleton of Omo I as anatomically modern yet have often noted features in its anatomy that are unusual in comparison to recent humans. The present study presents an analysis of linear measurements of many portions of the skeleton in comparison to several samples of recent (Holocene) humans. Special attention is paid to contrasts with Zulu males, a sample that approximates Omo I in overall size. The results show that Omo I has a long humerus with a slender shaft, a proximally positioned ulnar tuberosity, a short olecranon process, large articular ends and flattened proximal articular surface of the first metacarpal, a large acetabulum, a narrow patellar notch, and a low talus with a long neck. These join the set of distinctive features identified in previous analyses and combine to push the skeleton away from recent humans in multivariate space. A few of the features appear to be plesiomorphic, others apomorphic and ‘modern’, and some possibly idiosyncratic. Close inspection of the unusual dimensions suggests that some are unreliable, including the original estimate for humeral length. This implies that Omo I had a stout rather than linear build.