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

Size and shape in the primate forelimb


1Evolutionary Anthropology, Duke University, 2Institute for Human Origins, University of the Witwatersrand

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The forelimb is well-represented in the primate fossil record. Many forelimb features are understood to be functionally integral to locomotion. The forelimb must also balance manipulative ability with locomotion, and has likely experienced complex selection pressures. However, morphology cannot be considered independent of phylogeny or body mass. Previous research supports the macroevolutionary hypothesis that body size may be more evolutionarily labile than aspects of shape. One explanation for this is that natural selection more frequently targets body size than morphology; an alternate hypothesis states that shape traits are under stabilizing selection while body size is under directional selection. Macroevolutionary size-shape contrasts in Mammalia have largely been restricted to dental traits, perhaps due to the perception that these are less subject to homoplasy than postcranial traits. However, analyses of the primate skeleton found no significant differences in levels of homoplasy among cranial, postcranial, and dental traits. This study addresses the body size hypothesis using size-shape contrasts of the primate forelimb, including 38 shape variables from the humerus, ulna, and radius of 40 extant primate genera. Pairwise cosine similarity was calculated for species means. A matrix of the cosine similarities, along with a pairwise body size distance matrix, was correlated with a matrix of pairwise divergence dates. Results indicate that while size and shape have significantly different relationships with divergence time, body size differences have a stronger relationship with divergence time.

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