Defining hominidae

Abstract

A array of relevant cranial, postcranial, and dental morphologies are reviewed in an attempt to delineate shared derived features that would unite a group that includes extant humans and their fossil relatives to the exclusion of other hominoids. This group is now often referred to as tribe Hominini, but systematic practicality suggests that family Hominidae be retained, since the lower rank de facto limits even current, and certainly future, recognition of subclades. Potential hominid postcranial synapomorphies include a distinct angle at L5-S1, a long pubic ramus, a superoinferiorly short ilium that is roundedly expanded posteriorly, some thickening in the region of an iliac (crest) tubercle, a well-developed and knoblike anterior inferior iliac spine that lies noticeably superior to and somewhat back over the superior acetabular rim, a defined and deep greater sciatic notch, differential distribution of cortical bone of the femoral neck, anteroposteriorly long femoral condyles, and an outwardly slanted femoral shaft. Although “a weakly defined linea aspera” and “a concave rather than convex medial tibial condylar facet that lies level with the primitively concave lateral facet with the two facets being separated by a pair of distinct tibial tubercles” have been suggested as hominid apomorphies, this appears not to be the case-unless the apelike specimens commonly taken as hominid (e.g., from Hadar) are not. The only possible cranial feature appears to be alignment in the adult of the biporionic chord and basion (on the anterior margin of the foramen magnum). Derived dental features that might unite Hominidae also characterize an orangutan clade and thus must be explained away (e.g., as homoplasies) or dismissed as phylogenetically relevant in order to justify the former group. Of further note is the presence of Pongo clade-like facial features in australopiths and various specimens of Homo. These and the dental similarities suggest that focusing on Pan alone as the out-group from which to judge hominid-defining features is comparatively too narrow and, consequently, phylogenetically misleading. Within Hominidae, various subclades can be justified, suggesting that the relationships of various specimens referred to genus Homo lie within a clade that also subsumes “australopiths.” Much work remains before clade Hominidae can be more fully defined.