The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)


Clavicular Curvature and Locomotion in Anthropoid Primates: A 3-D Geometric Morphometric Analysis

NICOLE SQUYRES.

Functional Anatomy and Evolution, Johns Hopkins University

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As an essential component of the primate shoulder, the clavicle should reflect locomotor adaptations. While previous work has generally focused on measurements of clavicular length and torsion, the shape of clavicular curvature may better distinguish taxa and provide additional information about upper limb use in locomotion.

In this study, sliding semi-landmarks were placed on clavicles of 10 Anthropoid primate species (total n=96) that display a range of locomotor behaviors. Landmarks (k=37) were chosen to capture the overall curvature of the clavicle in three dimensions. Procrustes superimposition and principal components analysis show separation among taxa and several patterns of shape change in clavicular curvature that appear to be associated with locomotion and relative scapular position.

A superior curvature in the lateral part of the clavicle is related to the relative position of the scapula and sternum (e.g., extreme curvature in Alouatta associated with an enlarged vocal apparatus, and very little in Homo associated with the relatively low position of the scapula). An inferior curvature of the medial clavicle is found only in Hominoids and brachiators. This curvature could help stabilize the shoulder and prevent superior dislocation of the clavicle in suspension. Finally, the degree of anterior bowing in the clavicle represents a gradient from most-bowed in suspensory genera (brachiators and Pongo) to least-bowed in frequently terrestrial genera (Papio and Gorilla). This curvature may allow an increased range of craniodorsal movement without the clavicle impinging on the thoracic outlet. Clavicular curvature successfully distinguished among taxonomic and locomotor groups.

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