The Functional Morphology of the Lower Cervical Spine in Non-Human Primates

Susan R. Mercer

PhD Thesis. 1999

Review of the literature reveals a dearth of studies concerned with the functional morphology of the lower cervical vertebral column in non-human primates. There is disagreement about how much morphological specialization is evident in the vertebral column with some suggesting that little occurs, while other state that significant adaptations to positional behavior are evident. The purpose of this study was to examine the functional morphology of the lower cervical spine in six pairs of closely related non-human primate species or subspecies to determine whether the lower five cervical vertebrae exhibit differences in morphology that may be related to presumed differences in positional behavior. Specifically, the hypotheses to be tested were that there would be differences in osteometric indices, and that morphological features would show a similar pattern of differences when comparing the more arboreal versus the more terrestrial in each comparison pair. The comparison pairs were Galago senegalensis and Galago crassicaudatus; Macaca fascicularis and Macaca nemestrina; Cercopithecus mitis and Cercopithecus neglectus; Papio hamadryas hamadryas and Papio hamadryas anubis; Pan paniscus and Pan troglodytes; and Gorilla gorilla gorilla and Gorilla gorilla beringei.

Sixteen linear and two angular measurements of 940 lower five cervical vertebrae were taken using digital calipers. The linear measurements were then size adjusted in order to allow for comparison between the subspecies or species. Statistical analysis of inter-specific differences, both of individual indices, and of the collected sets of observations were designed to address two functional aspects of lower cervical vertebral morphology; stability and mobility. The results indicated a significant pattern of differences in the shape of the vertebral body (p<0.05) and the width of the posterior tubercle (p<0.01) as well as many other individually significant differences. It was concluded that subtle differences directed predominantly towards satisfying demands of stability associated with reported positional behavior exist, indicating that the lower cervical spine does exhibit morphological specialization.