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

Comparative analysis of covariance structure in the skull and postcranial skeletons of living apes


1Anthropology and Classical Studies, University of Akron, 2Community and Family Medicine, Duke University School of Medicine, 3Evolutionary Anthropology, Duke University, 4Anatomy and Neurobiology, Northeast Ohio Medical University

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Living apes exhibit striking locomotor diversity compared to other primate clades. The marked variation in locomotion underlies significant variation in skeletal morphology. These differences in postcranial form and locomotor behavior have lead anthropologists to argue that living apes evolved primarily as a “postcranial radiation”. While skull and postcranial traits have been compared among apes, we have little understanding of how covariance structure differs between postcrania and skulls. Here, we compare covariance structure between skulls and postcrania in modern humans, chimpanzees, bonobos, gorillas, mountain gorillas, orangutans and gibbons (all N>20 individuals per species and skeletal region). In the postcrania, we consider limb lengths, midshaft and joint dimensions. Skull measures focus on functionally-relevant variables related to food processing. We created shape variables by dividing postcranial measurements by limb lengths and skull measures by jaw length. We calculated correlation matrices from shape variables per group after mean-centering by sex and subspecies. Preliminary results offer little evidence for systematic differences in covariance structure between postcrania and skulls. The relative standard deviation of eigenvalues from correlation shape matrices suggests African apes and gibbons retain higher levels of integration in skulls compared to postcrania. Humans and orangutans show the opposite pattern. Contrary to a predicted increase in postcranial variation among species, pairwise comparisons of shape matrices among apes suggest more similarity in postcranial correlation structure compared to skulls. Additional comparisons will examine regional variation within postcrania and skulls and comparisons among locomotor/feeding subgroups. These initial results suggest a complex pattern of skeletal covariance evolution in apes.

Grant Support: NSF, Leakey Foundation, Sigma Xi

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