Clavicle

Although there are a number of fossil clavicular specimens known for early hominins (Table 7.1), most are only small segments and attempts to interpret them have been limited. The most complete specimen missing only a portion of its sternal end is A.L. 333x-6/9 (Lovejoy et al., 1982) attributed to A. afarensis. On the basis of the orientation of its lateral end on frontal view and the position of the deltoid attachment area, Ohman (1986) concludes that A.L. 333x-6/9 is distinct from extant hominoids, which he interprets as evidence of descent of hominin shoulder by three to four million years ago. However, Voisin's (2006) analysis of clavicular shape in primates indicates that the low scapular position of humans is reflected in curvature of the medial half of the clavicle (in A/P view) rather than that of the lateral end. Since the medial half of A.L. 333x-6/9 is apparently not unlike that of extant hominoids, it is possible that A. afarensis still retained a similar high shoulder position. More recently, Partridge et al. (2003) have described a partial clavicle from Jacovec Cavern at Sterkfontein (StW 606), attributed to Australopithecus sp., and note that it displays a pronounced conoid tubercle like chimpanzees and unlike other hominin clavicles including modern humans. This suggests that there may be some diversity in clavicular morphology among early hominins. However in general, these clavicular fossils offer very limited information on pectoral girdle/shoulder form and function in early hominins.

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