Department of Family and Community Medicine, Northwestern University
Saturday All day, Plaza Level
Modern humans have been reported to be unique among the hominoids in having strongly ventrally deflected midfaces when palate orientation is measured relative to the posterior cranial base (PCB). The current study considers facial orientation in a phylogenetic context and relative to multiple registration planes to test whether hyper-ventral palate flexion is a derived feature of modern H. sapiens to the exclusion of Pan, the sister group to the Hominina.
Midfacial orientation was quantified on lateral radiographs of modern Homo sapiens (n= 80) and Pan troglodytes (n=53) by measuring angles formed between the palate and four reference planes: a perpendicular to the orbital axis (POA); a perpendicular to the Frankfort horizontal (PFH); the posterior maxillary (PM) plane; and, the PCB. Raw, interspecific adult mean angular values of Homo and Pan were contrasted using one-tailed t tests. Homo angle means were further compared to the other hominoid genera.
In palate orientation measurements made relative to the POA, PFH, and PM planes, Homo did not have more ventral midfacial angles than Pan. In fact, Homo demonstrated relatively dorsal values for palate orientation that approached the hylobatid condition. Relative to the PCB registration plane, Homo was markedly derived from Pan and other hominoids with a highly ventral palate orientation. These results suggest earlier findings of ventral facial orientation in Homo may have been unduly influenced by the relatively flexed orientation of the PCB in Homo. Implications for the homology of facial orientation and for evaluating various evolutionary scenarios of hominoid evolution are discussed.