A Regression Analysis of Australopithecine Dentition

The permanent dentition of all known Australopithecines (except those from Hadar) are examined for size trends related to temporal and geographic variation. The Australopithecine sample is divided into four major groups for analysis: gracile Australopithecines, robust Australopithecines, ''Homo", and unknown. Mesiodistal and buccolingual dimensions for each tooth are then subjected to regression analysis. To discern temporal variation in tooth size for any of the taxonomic groups, a regression of tooth size with the median date of the specimen is performed. In order to elucidate dental variation related to geographic location, a regression analysis of tooth size with the latitude and longitude location of the hominid is undertaken.

The posterior dentition of the robust group appears to significantly increase in size through time whereas the gracile and "Homo" groups show a decrease in the anterior dental dimensions when analyzed separately, and exhibit a decrease in posterior tooth size when a combined analysis is performed. Metric variation related to geographic location of the specimen is not as easily interpreted as the temporal variation. The few dental dimensions which proved to be significantly related to location in East or South Africa were obtained by a combined analysis of all taxonomic groups in East Africa and all taxonomic groups in South Africa. Generally, molars tend to be larger in the southwestern region of South Africa and incisors show increased dimensions in the southwestern region of East Africa. Molar dimensions are largest in northeastern East Africa.

With our present knowledge, variation in tooth size cannot be related to macroenvironmental differences among these Plio-Pleistocene hominids, nor to dietary factors or differential tool use. Body size differences and craniofacial evolution are viewed as possible explanations for the various trends in the dentition related to temporal variation. Climatic factors could be partly responsible for dental size trends based upon geographic location of the specimen.