Variability of the hominid juxtamastoid eminence and associated basicranial features

Abstract

The juxtamastoid eminence is a ridge of bone associated with the attachment of the posterior belly of the digastric muscle. It is found in some hominids, but not in other primates, and is therefore considered to be a derived feature. We dissected 30 human cadavers and studied 229 modern human skulls to assess the range of variation and functional morphology of the juxtamastoid eminence. It was found that the mastoid region was highly variable both in form of the juxtamastoid eminence as well as in its relations to muscle attachments and adjacent bony features. In light of our observations, the mastoid regions of original hominid fossils from southern Africa were scrutinized. It was concluded that the fossils showed variability in the presence of the juxtamastoid eminence, and that the ambiguity of the mastoid region's preservation and interpretation was too great to use the eminence as a reliable taxonomic or phylogenetic indicator.