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

The comparative and functional anatomy of the forelimb musculature of Humboldt’s woolly monkey (Lagothrix lagotricha)


1Department of Anthropology, Eastern Kentucky University, 2College of Health Sciences, University of Kentucky, 3Department of Anatomy and Neurobiology, University of Kentucky College of Medicine, 4Department of Anatomy and Cell Biology, Indiana University School of Medicine, 5Department of Rehabilitation Sciences, University of Kentucky College of Medicine

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Humboldt’s wooly monkey (Lagothrix lagotricha) is a ‘tail-assisted’ brachiator similar to other members of the subfamily Atelinae, however that taxon more frequently engages in non-suspensory forms of locomotion (i.e. quadrupedal climbing). As a group the atelines share a suite of derived forelimb skeletal characters that are specialized for brachiation and that are convergent with ‘true’ brachiators (Hylobates, Symphalangus). The forelimb skeletal anatomy of lagothrix is similar to more suspensory atelines (Ateles, Brachyteles) and ‘true’ brachiators, but is typically less derived and many skeletal characters are intermediate between those forms and non-suspensory anthropoids. Although the functional morphology of the ateline skeletal forelimb is well documented, relatively little is known about the comparative and functional morphology of the forelimb musculature. Specifically, can locomotor differences between Lagothrix and more suspensory atelines and hylobatids be explained, in part, as a result of differences in muscle-tendon architecture?

This study provides quantitative anatomical data on the muscle–tendon architecture (muscle mass, physiological cross-sectional area, fascicle length) of the forelimbs of Lagothrix, Symphalangus and Macaca (n=9). Despite less frequent brachiation, the distribution of Lagothrix forelimb muscle mass and force is identical to similar results obtained for Symphalangus and with published data for Hylobates. Specifically, Lagothrix resembles hylobatids in the concentration of muscle mass and force in the flexor compartments of the arm and forearm. This suggests that despite a reduced reliance on suspensory postures and brachiation, Lagothrix forelimb muscle-tendon architecture may be, at least in part, a response to the minimum functional demands of brachiation.

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