The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)

The functional morphology of the scapula


Anthropological Institute, University of Z├╝rich

Saturday All day, Plaza Level Add to calendar

The shoulder girdle is an ideal anatomical area for studying the locomotion of primates and early hominids because it is involved in nearly every act of locomotion. Paying special attention to the form of locomotion, we can identify several features on the scapula that differ among the different species.

For this study the scapula of humans, chimpanzees, orang-utans, gibbons, gorillas and baboons were analysed (total n=286) and compared to casts of the scapula of A.L. 288-1 (Au. afarensis), Sts 7 (Au. africanus), Stw-431 (Au. africanus), MH2 (Au. sediba) and KNM WT 15000 (Homo erectus) and pictures of DIK 1-1 (Au. afarensis). For the measuring of the scapula, landmarks were defined, digitised by using the MicroScribe-3DX and later transformed into distance measurements.

The results of the scapular index, the supra- and the infraspinous index showed us that the long and narrow form of the hylobatid scapula reflects a specialisation of the shoulder for brachiation while the human scapula is wider than long and shows the reduced amount of external stress on the scapula due to its release of all direct duties of locomotion.

The small axilloglenoid angle we found in gibbons but also in the orang-utan, chimpanzee and the Australopiths helps to place the arm in an overhead position, ideal for brachiation and climbing, whereas in humans and quadrupedal primates (baboon and gorilla) we found a higher value for this angle, which reflects an adaptation of the arm for its use in a lower position of the joint axis.

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