Microtomographic analysis of fossil dental tissue of Neanderthal in situ maxillary and mandibular teeth from Krapina (Croatia, 130 ka)

Comparative morphometric analysis of the Neanderthal dentition has contributed significantly to our understanding of the biology and phylogenetic relationships of this extinct hominin taxon which displays a species-specific pattern of dental traits, in terms of both morphology and ontogeny. Specifically, enamel thickness and dental tissue proportions have been widely used traits in making taxonomic decisions and subsequent phylogenetic inferences among hominins and within the genus Homo. This preliminary work presents results of volumetric analysis on a sample of 43 in situ permanent teeth from 5 mandibles and 3 maxillae, belonging to 8 different individuals from the site of Krapina (Croatia,130 ka). The remains were discovered in 1899 AD and yielded, to date, the largest collection of fossils attributed to H. neanderthalensis from a single locality. The fossil specimens were measured by X-ray computed microtomography (XµCT) at Elettra Synchrotron facility in Basovizza (Trieste, Italy) using the FAITH instrument equipped with a microfocus source. Volumes were reconstructed with pixel sizes of 35 µm and 55 µm, and subsequently partitioned by semi automatic segmentation. A subsample (N=23) of unworn teeth were selected for dental tissue proportions (DTP) analysis. Following protocols previously reported in the literature, bucco-lingual diameters, coronal tissue volumes and topographic changes in enamel thickness were calculated. The indices obtained were then compared with a large comparative set for Neanderthals obtained from the literature. Preliminary results suggest considerable intra-population variability among the Krapina individuals and, in general, the average tooth dimensions exceed the average of the Neanderthal comparative set. In particular, the analysis of the maxillary and mandibular dentition reveals that almost all teeth analysed exhibit greater volume in the tissues’ coronal portion and enamel, as well as a greater diameter. The relative enamel thickness also follows a similar pattern, although there are differences between the anterior and posterior maxillary dentition. This is due to the Krapina specimens having larger molars and premolars, but smaller incisors when compared to the Neanderthal average. This places the Croatian sample at the upper end of Neanderthal phenotypic variation, as well as substantially enriching the high-resolution digital documentation of Neanderthal fossil dental specimens. Furthermore, our preliminary results highlight the importance of integrated morphological analyses for the purpose of taxonomic inferences, as it is the “whole package” of anterior and posterior dental proportions that most strongly distinguishes the Krapina group from the rest of the Neanderthals. Finally, our findings seem to underscore a significant between-group variability in H. neanderthalensis, possibly the result of strong genetic isolation between groups, as extensively highlighted by recent aDNA research.