Center for the Study of Human Origins, Department of Anthropology, New York University, New York Consortium in Evolutionary Primatology
April 21, 2017 8:45, Bissonet
The cervical vertebrae play an important role as mediators between the cranium and postcranium, an interaction that is especially interesting in bipedal hominins. However, little is known about cervical vertebral evolution. Although the cervical vertebrae are developmentally linked to the cranium, many authors have posited that the cervical column evolves primarily in response to locomotion and posture. If so, we should expect that integration among cervical elements and the cranium will vary between taxa with different locomotor and positional behaviors, more closely reflecting biomechanical selective pressures than developmental ones. To test this hypothesis, I collected linear measurements on the basicranium and cervical vertebrae of Homo (n=120), Pan (n=114), and Hylobates (n=92). Magnitudes of integration (MI) were calculated for each taxon using the mean integration statistic. Although there exist differences in MI between taxa and Homo displays generally lower MI than both Pan and Hylobates, overall patterns of integration are the same. In all three taxa, the cervical vertebrae are strongly integrated with the basicranium (MI=0.78-0.89), often more so than they are with each other or as isolated elements, and vertebrae C3 through C6 form an integrated module (MI=0.84-0.92). These results do not support the hypothesis that the cervical column is evolving in response to locomotor behaviors, but rather suggest the cervical vertebrae evolve in response to changes in cranial morphology. Differences in the cervical column between hominins and other hominoids, thus, are likely the result of the uniquely derived skull of hominins rather than the adoption of bipedalism.
This research was funded by New York University and the Wenner-Gren Foundation.