Department of Anthropology, Stanford University
Thursday 9:15-9:30, Grand Ballroom II
The evolutionary descent of the shoulder is proposed to have occurred after or with the evolution of Homo. Unfortunately, the previously known sample of Australopithecus clavicles did not preserve many distinguishing anatomical features. The partial skeleton KSD-VP-1/1, recently discovered at Woranso-Mille (Afar, Ethiopia), preserves the most complete adult clavicle assigned to Australopithecus afarensis. Clavicle length, torsion and curvature are thought to indicate scapula position, shoulder width and/or shoulder height, but no consensus exists regarding the anatomical implications of morphology preserved in the Australopithecus sample. I used a combination of Geometric Morphometric and traditional comparative methods to describe morphological variation in the living apes and Australopithecus.
The curvature of the human clavicle is distinctive among living apes. With the preservation of the medial shaft, KSD-VP-1/1f demonstrates human-like curvature for the first time in Au. afarensis. Although KSD-VP-1/1f falls comfortably within the range of human clavicle length and torsion, more information is needed in order to reconstruct shoulder configuration. Torsion is thought to reflect overhead use of the arms, but this character does not vary in a functionally informative manner within the apes.
The shoulder is a complicated joint complex with many constituent parts, making functional inference from isolated elements difficult. Vital regions are still missing from the fossil sample, but the data emerging from the study of the KSD-VP-1/1 partial skeleton suggest a unique configuration of the Au. afarensis shoulder that is more like that of modern humans than has been previously proposed.
This research was supported by the Leakey Foundation and the National Science Foundation (BCS-0542037).