Enamel thickness and dental tissue proportions in the Neandertals from the Sima de las Palomas del Cabezo Gordo, Southeastern Spain
Résumé
Enamel thickness and dental tissue proportions have been studied frequently to assess taxonomy, phylogeny, and masticatory biomechanical constraints in fossil and extant hominoids [1]. Many studies have focussed on Neandertals and their comparison with modern humans [2]. By and large, Neandertal deciduous and permanent teeth (mainly molars) have been described as having similar enamel volumes to modern humans, albeit deposited over a topographically more complex enamel-dentine junction surface and with larger dentine volumes. Thereby Neandertal teeth show thinner average and relative enamel thicknesses. However, few complete dentitions have been published, and little quantitative information is available on anterior teeth and premolars. Moreover, our limited knowledge about variation in Neandertal enamel thickness and dental tissue proportions does not permit evaluation of possible existence, or nature, of chrono-geographical trends in these fossil humans. Although sample sizes do not allow a proper evaluation, Olejniczak et al. [2] noticed that variation encompassed by Neandertal molars, spanning a substantial geographical and temporal interval, was less than in recent humans. Here we report on results of microCT-based analysis of enamel thickness and dental tissue proportions in Neandertal teeth from Sima de las Palomas del Cabezo Gordo (SPCG, Torre Pacheco, Murcia, Spain). They are compared to data for Middle, Late Pleistocene and Holocene archaic and modern humans. Besides providing a unique opportunity to study the homogeneity of these parameters in a constrained chrono-spatial context, this report substantially increases the range of Neandertal variation known so far, notably for deciduous and anterior permanent teeth. Dating plausibly from ca. 55-50 ka cal BP (within outermost limits of ca. 64 and 38 ka cal BP), 300 skeletal fragments from SPCG correspond to 9 or more Neandertal individuals, and include articulated parts of 3 adult skeletons [3-4]. 31 SPCG teeth were examined for enamel thickness and tissue proportions. All the teeth chosen were well preserved, free of damage, and unworn to slightly-worn on their occlusal aspect. Teeth were scanned on Skyscan 1172 X-ray equipment transported to the Department of Zoology and Physical Anthropology at the University of Murcia from the Department of Archaeology and Anthropology of the University of Bristol. We used Nrecon v.1.6.6 (Skyscan) to reconstruct the final volumes with an isotropic voxel size ranging from 21 µm for isolated teeth to 36 µm for jaw fragments. After segmentation, 13 linear, surface, and volumetric variables were measured or calculated for describing 3D and 2D tissue proportions and enamel thickness, and 3D maps of topographical enamel thickness distribution were created. On the whole, the SPCG internal tooth structure is in line with the Neandertal range of variation for deciduous and permanent dentition and for all tooth positions. Nevertheless, the deciduous and permanent upper SPCG incisors show a different signal from the rest of the dentition as measured on permanent teeth of other Neandertals [5]. However, for several teeth the SPCG data extend the range of Neandertal variation known hitherto.They also show noteworthy variation within tooth types, suggesting that Neandertal intra- and inter-population variation in internal dental structure is still far from having been documented. References:[1] Pampush, J.D., Duque, A.C., Burrows, B.R., Daegling, D.J., Kenney,W.F., McGraw, W.S., 2013. Homoplasy and thick enamel in primates. J. Hum. Evol. 64, 216-224. [2] Olejniczak, A.J., Smith, T.M., Feeney, R.N.M., Macchiarelli, R., Mazurier, A., Bondioli, L., Rosas, A., Fortea, J., de la Rasilla, M., García-Tabernero, A., Radovcic, J., Skinner, M.M., Toussaint, M., Hublin, J.-J., 2008. Dental tissue proportions and enamel thickness in Neandertal and modern human molars. J. Hum. Evol. 55, 12-23. [3] Walker, M.J., López-Martínez, M.V., Ortega-Rodrigáñez, J., Haber-Uriarte, M., López-Jiménez, A., Avilés-Fernández, A., Polo-Camacho, J.L., Campillo-Boj, M., García-Torres, J., Carríon-García, J.S., San Nicolás-del Toro, M., Rodríguez-Estrella, T., 2012. The excavation of buried articulated Neanderthal skeletons at Sima de las Palomas (Murcia, SE Spain). Quatern. Int. 259, 7-21. [4] Trinkaus, E., Walker, M.J. (Eds.), In press. The People of Palomas: The Neandertals from the Sima de las Palomas del Cabezo Gordo, Southeastern Spain. Texas A&M University Press, College Station, Texas. [5] Smith, T.M., Olejniczak, A.J., Zermeno, J.P., Tafforeau, P., Skinner, M.M., Hoffmann, A., Radovčić, J., Toussaint, M., Kruszynski, R., Menter, C., Moggi-Cecchi, J., Glasmacher, U.A., Kullmer, O., Schrenk, F., Stringer, C., Hublin, J.-J., 2012. Variation in enamel thickness within the genus Homo. J. Hum. Evol. 62, 395-411.