Maxillary Molar Enamel Dentine-Junction Shape Differences between Krapina Neanderthals and Modern Humans

Abstract

Archaic and modern humans differ in a range of craniodental features. From a taxonomic and phylogenetic perspective, it is essential to distinguish between species accurately through detailed morphological characterizations. This study analyzes the size and shape variation of the enamel-dentine junction (EDJ) of upper molars from two hominin species, early Neanderthals from Krapina (N = 13) and mid-Holocene European modern humans (N = 14), to assess the extent of their endostructural morphological differentiation. The EDJ was obtained through microtomographic scans of each molar using segmentation procedures. Three-dimensional landmarks semilandmarks and 3D geometric morphometric methods were employed to investigate EDJ size and shape variation through univariate (t-test), multivariate exploratory, and classification methods (PCA and LDA). The results indicate that the shape of the EDJ and cervix of M2 differentiates Krapina Neanderthals from mid-Holocene European modern humans with a high degree of accuracy (~85%). Furthermore, EDJ size and dental nonmetric traits expressed in this structure provide additional information that is useful for distinguishing between the two species. Compared to modern humans, Krapina Neanderthals exhibit reduced dental diversity. From an endostructural perspective, this study provides additional insights into early Neanderthals´ morphological diversification relative to modern humans, which is valuable for studying middle and late Pleistocene hominin evolution.