Brief communication: foramen magnum-carotid foramina relationship: is it useful for species designation?

The anterior placement of the foramen magnum is often used to indicate bipedalism and therefore to distinguish hominid from nonhominid fossils. Often, only fragmentary cranial remains are found, and the placement of the foramen magnum must be determined by its relationship to another landmark. The purpose of this study was to test if hominid crania could be distinguished from nonhominid crania based on the relationship between the foramen magnum and the carotid foramina, and therefore to determine if the carotid foramina can be used to determine the anteriorness of the foramen magnum. The samples consisted of 16 modern human crania and 19 modern chimpanzee (Pan troglodytes) crania. Linear measurements were taken of (1) the distance from the anterior border of the foramen magnum to a chord connecting the carotid foramina and (2) total cranial length. An index of the distance of the foramen magnum from the bicarotid chord as a proportion of total cranial length was calculated to control for differences due to body size. Results indicate that on average, human crania can be distinguished from chimpanzee crania by using either (1) the distance of the foramen magnum from the bicarotid chord as a linear measurement or (2) this linear measurement as a proportion of total cranial length. Both measures are significantly smaller in the human sample; however, there was considerable overlap between species, indicating that the distance of the foramen magnum from the bicarotid chord is not a certain indicator for individual specimens.