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

Can caudal vertebral body articular surface shape discriminate among prehensile and non-prehensile tailed anthropoids?


1Department of Anatomy and Neurobiology, University of Kentucky College of Medicine, 2Department of Surgery, Saint Louis University School of Medicine

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The prehensile tail, capable of suspending the entire body weight of an animal, has evolved twice (in parallel) in New World monkeys (Platyrrhini): once in the monophyletic Atelinae (Alouatta, Ateles, Brachyteles, Lagothrix), and once in Cebus. Structurally, the prehensile tails of atelines and Cebus share morphological features that distinguish them from non-prehensile tails, including longer proximal tail regions, well-developed hemal processes, robust caudal vertebrae resistant to higher torsional and bending stresses, and caudal musculature capable of producing higher contractile forces. The functional significance of shape variation in the articular surfaces of caudal vertebral bodies, however, is relatively less well understood. Given that tail use differs considerably among prehensile and non-prehensile anthropoids, it is reasonable to predict that caudal vertebral body articular surface area and shape will respond to use-specific patterns of mechanical loading.

Here we examine the potential for 3D shape analysis to discriminate among a mixed sample (n=22) of wild-shot prehensile- and nonprehensile-tailed platyrrhines and nonprehensile-tailed cercopithecoids. Proximal and distal caudal vertebral body articular facets for the first caudal vertebra, transitional vertebra and longest vertebra were laser scanned and modeled as quadric functions. Results indicate that the distal articular surfaces of prehensile tail caudal vertebrae are more convex (i.e. have more pronounced surface curvature) relative to nonprehensile tail vertebrae, and these differences are most pronounced in the longest vertebra. Pronounced articular surface curvature is potentially associated with enhanced lateral joint excursion, joint congruence or some combination of factors relating to postural stability of the tail during use.

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