1Center for the Advanced Study of Hominid Paleobiology, George Washinton University, 2Department of Archaeology, University of Sheffield, 3Department of Life Sciences, Roehampton University
Thursday 4:15-4:30, Ballroom C
The relatively small Australopithecus africanus specimen Sts 5 has been argued to be either an immature, small male or a mature female. Here we report on a CT-based analysis of the anterior dentition that informs this debate.
Sts 5 demonstrates extremely short tooth roots, particularly for the anterior dentition. Interestingly, these tooth roots are oriented vertically (relative to the alveolar plane), unlike those found in other apes, humans, and fossil specimens, in which the tooth roots are roughly parallel with the plane of the nasoalveolar clivus. Kaifu (2000) has a proposed a model of continuous eruption and angular change in humans: with progressive wear, anterior teeth continue to erupt throughout life and become more vertically oriented to maintain occlusion. As the anterior teeth continuously erupt, the roots also become more vertically reoriented.
We examined CT data of adult apes, humans, and fossil hominin specimens and documented a relationship between the angle of the anterior tooth roots and their length. The extremely short and vertically oriented anterior roots observed in Sts 5 thus suggest that the specimen represents an aged female specimen with extremely worn dentition. Interestingly, this reorientation of anterior tooth roots helps account for the extreme expression of subnasal prognathism of Sts 5 - in apes where there is considerable anterior tooth wear and the roots are reoriented as described, bony remodeling forms a bulge along the alveolus in the region of the roots, thus increasing the measured prognathism of the individual.