Further analysis of mandibular molar crown and cusp areas in Pliocene and early Pleistocene hominids

Abstract

Crown and cusp areas of mandibular molars were measured and analyzed on a sample of 249 specimens attributed to Australopithecus afarensis, A. africanus, A. (Paranthropus) robustus, A. (P.) boisei, and early Homo. In addition to intertaxon comparisons, we compared data that had been collected independently by two of the authors using methods that differ slightly in technique of measurement. Interobserver differences were evaluated by the t-test of paired comparisons, method error statistic, percent differences, and principal component analysis. Results suggest that between-technique error of measurement of overall crown area is small. Error estimates for individual cusp area measurements were of larger relative magnitude. However, these were not sufficient to detract from the conclusions derived from comparative analyses. Our results are in general agreement with previous assessments of early hominid dental size. Crown areas of A. africanus, however, exhibit a mosaic pattern, with M1 similar in size to that of A. afarensis and early Homo, and M2 and M3 similar in size to that of A. robustus. Intertaxon comparisons of relative cusp area were undertaken by univariate statistics and principal component analysis. These analyses revealed that while A. (P.) robustus and A. (P.) boisei both possess mandibular molars with cusp proportions significantly different from the 'non-robust' taxa, these differences are substantially greater in A. (P.) boisei.

A New Method of Evaluating Enamel Thickness Based on a Three-Dimensional Measuring Systems.

“…Magnitude of error, as expressed by the method error statistic, is broadly comparable to that of traditional mesiodistal and buccolingual crown dimensions (e.g., Mizoguchi, 1977) or of projected area measurements of the molar crown (Suwa et al, 1994). It can be concluded that the repeatability accuracy of our method of measuring enamel thickness is sufficient for actual use.…”

Mandibular postcanine dentition from the Shungura Formation, Ethiopia: Crown morphology, taxonomic allocations, and Plio-Pleistocene hominid evolution

“…tion of these is available in Suwa (1988, one-way ANOVA tests on taxon means, while 1990, in press) and Suwa et al (1994) and principal components and canonical variate is not repeated here.…”

The Evolution of Zinjanthropus boisei

“…A 53 noted that ''the individual cups involved in the talonid expansion are not always the same,'' with the hypoconid and the entoconid contributing more to talonid expansion in P. boisei and P. robustus, respectively. This suggests that the derived dental morphology in the two Paranthropus taxa may not have the same developmental basis.…”