Premolar root and canal variation in South African Plio-Pleistocene specimens attributed to Australopithecus africanus and Paranthropus robustus.

South African hominin fossils attributed to Australopithecus africanus derive from the cave sites of Makapansgat, Sterkfontein, and Taung, from deposits dated between about 2 and 3 million years ago (Ma), while Paranthropus robustus is known from Drimolen, Kromdraai, and Swartkrans, from deposits dated between about 1 and 2 Ma. Although variation in the premolar root complex has informed taxonomic and phylogenetic hypotheses for these fossil hominin species, traditionally there has been a focus on external root form, number, and position. In this study, we use microtomography to undertake the first comprehensive study of maxillary and mandibular premolar root and canal variation in Australopithecus africanus and Paranthropus robustus (n = 166 teeth) within and between the species. We also test for correlations between premolar size and root morphology as predicted under the 'size/number continuum' (SNC) model, which correlates increasing root number with tooth size. Our results demonstrate previously undocumented variation in these two fossil hominin species and highlight taxonomic differences in the presence and frequency of particular root types, qualitative root traits, and tooth size (measured as cervix cross-sectional area). Patterns of tooth size and canal/root number are broadly consistent with the SNC model, however statistically significant support is limited. The implications for hominin taxonomy in light of the increased variation in root morphology documented in this study are discussed.

Premolar root and canal variation in extant non-human hominoidea.

OBJECTIVES: The premolar sub-cervical region in four non-human extant ape genera are examined to: 1) define a classification scheme for the premolar root system in order to rigorously characterize, quantify and document variation in root and canal, form, number and configuration; 2) compare this variation within and between genera; and 3) test the hypotheses that sex and size (i.e., the "size/number continuum," Shields, ) of the premolar are determinants of root/canal form and/or number. MATERIALS AND METHODS: Microtomography and 3D visualization software are utilized to examine a large sample of Hylobates, Pan, Gorilla, and Pongo (n = 951 teeth). Each premolar root system is examined to ascertain the expected level of variability for each taxon. Cervical surface area (mm2 ) serves as a metric proxy for tooth size. A Chi-square test of independence is used to assess for variability differences between and within each taxon, and Mann-Whitney U tests are employed to assess the predicted relationship between tooth size and variation within each taxon. RESULTS: Our findings indicate that root and canal configurations, non-metric root traits and tooth size can distinguish between extant ape genera. Within the four ape taxa, premolar size variation is generally, but not always, correlated with canal/root number. Our results indicate that males and females within genera differ in tooth size but not in canal/root form and number. DISCUSSION: We report previously undocumented variation in the study taxa. Our results are discussed within the context of Miocene Apes as well as the developmental and systematic implications. Am J Phys Anthropol 158:209-226, 2015. © 2015 Wiley Periodicals, Inc.

Premolar root morphology and metric variation in Pan troglodytes verus.

Premolar root form remains an important taxonomic character in hominin alpha taxonomy. Variation in detailed aspects of root structure remains poorly characterized in extant apes. This limited comparative context hinders evaluations of the significance of root form variation in hominin systematics. Using micro-computed tomography we examine morphological variation in premolars in 51 (n = 128 premolars) West African chimpanzees (Pan troglodytes verus). We categorize premolar root/canal form and number, based on the external root surface and pulp canal morphology, and test for a relationship between canal configuration and sex, jaw size, tooth/root size and cervix shape. Jaw size and root size/shape were quantified using standard metrics, and geometric morphometrics was used to examine root form and cervix shape. Our results confirm previous findings in external root form, but reveal previously undocumented variation in mandibular premolar canal number/form in this subspecies. The LP3 and UP4 exhibit variation in canal number/form, while the UP3 is restricted to external root configurations. The LP4 expresses only a single root/canal form. Generally, in LP3 and UP4 there is no correlation between canal form/number and sex, root size, and jaw size; UP4 canal variation covaried with cervix shape and size. Cervix size is significantly greater in three canal UP4s than two canal UP4s. Our results highlight canal form/number as an important aspect when characterizing root form. The implications of our results for the taxonomic utility of root form within the hominoid and hominin clades are discussed.