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

Stable thoracolumbar morphology: implications for terminal branch locomotion


1Department of Evolutionary Anthropology, Duke University, 2Division of Anatomy, University of Alberta, 3Department of Biomedical Sciences, West Virginia School of Osteopathic Medicine, 4Department of Anthropology, Yale University

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A stable thoracolumbar region found in some arboreal mammals and certain primates has been proposed as the primitive euarchontan condition and advantageous for bridging and cantilevering between discontinuous terminal branches. However, no data exist testing the inferred link between osteological features cited as enhancing whole-body stability and the frequency and mechanics of cantilevering and bridging in a terminal branch environment. To fill this gap we compared costal and vertebral morphology of primate and nonprimate mammals thought to cantilever and bridge frequently to those that do not. We also contrasted the frequency and kinematics of cantilevering and bridging of Caluromys philander and Loris tardigradus (fine-branch specialists), to Monodelphis domestica (terrestrial quadruped) and Cheirogaleus medius (active arboreal quadruped) on a raised horizontal pole and terminal branch experimental set-up. We observed C. philander cantilevering and bridging significantly more often (55% of observed events) than M. domestica, which never cantilevered or crossed any arboreal gaps (P <0.001). No difference in cantilevering frequency was observed between L. tardigradus and C. medius, but the duration of cantilevering bouts were significantly greater in L. tardigradus (4.24 sec ± 2.11 vs. 2.35 sec ± 1.71; P < 0.01). Cluster analysis reveals that C. philander and lorises exhibit thoracolumbar stability related to reduced intervertebral and intercostal spaces, when compared to closely related species like M. domestica and C. medius. These data suggest that osteological stability, which may have been present in the ancestral primate, may be part of a complex that increases security in a terminal branch environment.

Supported by National Science Foundation grants BCS-9904401, and 0749314.

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