Short communication: Traits unique to genus Homo within primates at the cervical spine (C2–C7)

Abstract

From a comparative study of 222 human and 261 nonhuman primates complete cervical spines, two bony variants associated to the course of the vertebral artery are proposed as unique to genus Homo within primates. First, the opening of the foramen transversarium at C2, a trait present at low frequency in humans (3 to 5.6%). Second, the presence of a bipartite foramen transversarium in the cervical segment C3–C6, a trait that can be observed fully formed in human fetal skeletons, with a clear frequency pattern along the cervical spine (C3 > C4 > C5 > C6 < C7), and the expression of which does not seem to be significantly associated to sex or side. A clear difference is observed in the frequency of a third trait, the foramen transversarium at C7, present in all the human spines studied, practically absent in Strepsirrhini, at low frequency in Platyrrhini, and generalized in Catarrhini. These findings, together with previous data regarding absence and presence of foramina at C1, indicate a pattern of gain and loss of foramina in the transverse process of the cervical vertebrae for genus Homo. The test of a possible explanation of these differences as associated to anatomical changes of the cervical spine due to erect posture and bipedal locomotion needs further research in the morphology and function of the primate cervical spine.