Secular change has been documented in a number of studies focused on cranial and postcranial morphometrics and nonmetric traits. However, to date, few studies have addressed the potential of temporal change occurring in the expression of cranial nonmetric traits utilized in ancestry estimation. This study examines the effect of secular change on the expression of 23 cranial and mandibular nonmetric traits frequently employed in ancestry estimation; with age-at-death, sex, and year-of-birth of each individual documented for data analysis. Data were collected from European American individuals from the Hamann-Todd Skeletal Collection (n=518) and from the William M. Bass Donated Skeletal Collection (n=602). Individuals were divided into birth-year cohorts as follows: Hamann-Todd Skeletal Collection: 1824-1849 (Cohort 1), 1850-1874 (Cohort 2), 1875-1899 (Cohort 3), and 1900-1924 (Cohort 4); William M. Bass Donated Skeletal Collection: 1900-1924 (Cohort 4), 1925-1949 (Cohort 5), and 1950-1987 (Cohort 6). Pearson’s chi-square analyses produced significant p-values (≤ 0.01) in 19 of the 23 traits between the six birth-year cohorts. Factor maps generated through correspondence analyses were used as visual representations of relative trait expression between the cohorts. Ordinal regression analyses assessed the degree of variation between each cohort in relation to Cohort 1 along with the influence of age-at-death and sex on trait expression. Overall, analyses of the data revealed that secular change has occurred in 11 of the 23 traits, including: anterior nasal spine (ANS), malar tubercle (MT), nasal bone contour (NBC), postbregmatic depression (PBD), supranasal suture (SPS), transverse palatine suture (TPS), zygomaticomaxillary suture (ZS), gonial angle flare (GAF), mandibular tori (MDT), and posterior ramus edge inversion (PREI). Change in trait expression occurred in both males and females in seven traits, including: ANS, MT, TPS, ZS, GAF, MDT, and PREI. Significant change in trait expression occurred predominately between Cohorts 3 and 4 (birth years ranging from 1875 to 1924) and Cohorts 4 and 5 (birth years ranging from 1900 to 1949). This study demonstrates that secular change in nonmetric cranial and mandibular traits has occurred over the last two centuries with the greatest change appearing at the turn of the twentieth century.

Traditionally, pre-contact Native Americans have served as a biological reference for identifying modern Asian individuals in aspects of the biological profile due to their distantly shared genetic history, although this assumption remains largely untested. This study explores the craniomorphic variability between Asian and Asian-derived groups to ascertain whether they can be differentiated using population-specific models. Cranial and mandibular nonmetric trait data were recorded on pre-contact Native Americans (n=150) and compared within a statistical framework to cranial trait data for modern Thai (n=150) and Japanese (n=150) individuals. Chi-square analyses indicate that the groups exhibit statistically significant differences in their trait expressions. Of the 35 traits analyzed, 31 differ significantly between the groups. Binary logistic regression equations for differentiating the Japanese, Thai, and Native Americans are presented, and cross-validated correct classification rates range 60.0-90.0%. Further, the inclusion of sex into the logistic regression equations failed to improve their accuracies. The results indicate that the Native American and Asian groups are not skeletally homogenous due to divergent population histories, and that numerous cranial and mandibular nonmetric traits are resolute enough to detect differences within and between Asian and Asian-derived groups. Thus, this study highlights the utility of nonmetric traits in identifying individuals beyond the traditional African (“Black”), (“White”), and Asian groupings.

Ce travail de thèse porte sur la variation exo- et endostructurale des couronnes des dents permanentes du maxillaire et de la mandibule chez les Néandertaliens et les Hommes modernes. Il intègre trois champs d’investigation faisant appel à l’imagerie a haute-résolution (e.g. μCT-scan) et a la 3eme dimension appliquées sur les canines, les prémolaires et les molaires. L’un de ces champs concerne l’épaisseur et la proportion de l’email 3D, le deuxième concerne la forme de la surface externe de l’email et de la jonction email-dentine (morphométrie géométrique 3D) et le dernier concerne les traits non métriques a la surface externe de l’email et à la jonction email-dentine. Cette étude comprend un échantillon microtomographique de 190 dents néandertaliennes, incluant les données inédites des dents de l’Hortus (Hérault, France) et du Portel-Ouest (Ariège, France) (n=45), et de 300 dents d’Hommes modernes. Les résultats montrent que l’approche 3D des couronnes dentaires au moyen de la microtomographie s’avère être très utile pour distinguer les Néandertaliens des Hommes modernes en termes d’épaisseur et de proportion d’email 3D pour la majorité des dents étudiées, a l’exception des M1/M1 et de la forme 3D du contour marginal de la JED de la majorité des dents. De plus, des différences dans l’organisation des tissus des couronnes ont été observées au sein de l’échantillon des Néandertaliens entre les spécimens de Krapina, pouvant être considères comme des premiers représentant de ce taxon (SIM5e, env. 130 ka) et ceux de l’Hortus et du Portel, pouvant être considérés comme des derniers représentants (SIM3, env. 44 ka) et dont l’organisation des tissus des couronnes dentaires se rapproche de celle des Hommes modernes. Cela suggère une importante variation intergroupe chez les Néandertaliens d’ordre géographique ou diachronique, lequel se traduirait par une réorganisation endostructurale des tissus coronaires en lien avec la réduction du volume absolu des couronnes dentaires. / This work focuses on the exo- and endostructural crowns variations of maxillary and mandible permanent teeth of Neandertals and modern Humans. It integrates three fields of investigation using high-resolution imaging (e.g. μCT-scan) and the third dimension applied in canines (excepted 3D geometric morphometrics), premolars and molars. One of these fields relates to the 3D enamel thickness and the 3D tissues proportion, the second concerns outer enamel surface and enamel-dentine junction shapes (3D geometric morphometrics), and the third concerns the nonmetric traits at the outer enamel surface and enamel-dentine junction. This study includes a sample of 190 microtomographic Neandertal teeth, including unpublished microtomographic data of Hortus (Hérault, France) and Portel-Ouest (Ariège, France) teeth (n = 45), and microtomographic sample of 300 modern Humans teeth. The results show that 3D approach of dental crowns using microtomography data is very useful to distinguish Neandertals from modern Humans in terms of 3D enamel thickness and tissues proportions (except for the M1 / M1), as well as in terms of the EDJ marginal edge shape, for the majority of studied teeth. Moreover, differences of tissues organization in crowns were observed within the Neandertal sample, between the Krapina specimens, that can be considered as a group of early Neandertals (MIS 5e, approx. 130 ka), and the Hortus and Portel specimens, that can be considered as a group of least Neandertals (MIS 3, approx. 44 ka) and show a tissues organization of dental crowns more similar to modern Humans. This suggests a significant geographic or diachronic inter-group variation among Neandertals that seems to relate endostructural reorganization of the coronary tissues to the reduction of the absolute volume of dental crowns.

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