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

Manual phalangeal curvature and locomotion in Primates


Anthropology Department, University of Massachusetts at Amherst

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Primate manual phalanges are directly affected by the loads inflicted during locomotion. The degree to which these elements are curved has been used to infer the use of suspensory or non-suspensory locomotion in primates. An index comparing the curvature values of middle and proximal phalanges of digit 3 (the Index of Relative Curvature) was shown to be successful at differentiating between knuckle walkers, quadrupeds, and brachiators. Given the rarity with which phalanges are recovered in the fossil record, and the difficulty of assigning such elements to the proper digits or individuals, it must be determined if the locomotor signal seen within digit 3 can also be seen: 1. in the other rays, 2. using elements attributed to different rays of the same hand, and 3. using elements attributed to different individuals of the same species. The present study extends previous analysis by examining the relative curvature of the proximal and middle phalanges of digits 2, 3, 4, and 5. The study includes knuckle-walking (Pan troglodytes and Gorilla gorilla), quadrupedal (Macaca spp. and Cebus apella), and suspensory primates (Pongo pygmaeus, Hylobates lar, and Ateles spp.). The Indices of Relative Curvature for digits 2-5 and those derived from middle and proximal phalanges of different rays retain the strong locomotor signals. This suggests that Indices of Relative Curvature can be applied successfully to fossils and other cases for which digit identity cannot be discerned, and for which isolated proximal and middle phalanges may not belong to a single digit.

Research supported by Wenner Gren Foundation for Anthropological Research and The Leakey Foundation.

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