Cervical and crown outline analysis of worn Neanderthal and modern human lower second deciduous molars

Abstract

Despite the general increase in digital techniques for dental morphometric analyses, only a few methods are available to study worn teeth. Moreover, permanent dentitions are studied much more frequently than deciduous teeth. In this study, we address both issues by providing a taxonomic classification of Neanderthal and modern human (MH) lower second deciduous molars (dm(2) s) through the analysis of crown and cervical outlines. Crown and cervical outlines were obtained from a three-dimensional (3D) digital sample of uniformly oriented dm(2) s. Both outlines were centered on the centroid of their area and represented by 16 pseudolandmarks obtained by equiangularly spaced radial vectors out of the centroid. We removed size information from the oriented and centered outlines with a uniform scaling of the pseudolandmark configurations to unit Centroid Size. Group shape variation was evaluated separately for the dm(2) crown and cervical outlines through a shape-space principal component (PC) analysis. Finally, quadratic discriminant analysis of a subset of PCs was used to classify the specimens. Our results demonstrate that both outlines successfully separate the two groups. Neanderthals showed a buccodistal expansion and convex lingual outline shape, whilst MHs have buccodistal reduction and straight lingual outline shape. Therefore, we confirmed that the cervical outline represents an effective parameter for distinguishing between the two taxa when dealing with worn or damaged dm(2) s.

Neandertal-Modern Human Contact in Western Eurasia: Issues of Dating, Taxonomy, and Cultural Associations

“…Where the corresponding Lagar Velho tooth is concerned, they found it to be intermediate between Neandertals and modern humans in crown outline, and described this fi nding as corroborating the similar conclusion derived by Bayle et al ( 2010 ) from tissue proportions. Benazzi et al ( 2012 ) also found that the crown outlines of three other fossils, two Neandertals and one Upper Paleolithic modern, were misclassifi ed by the predictive tool derived from the observed patterns. It is also noteworthy that the Neandertal sample in this study is composed of 14 specimens, of which 11 (those from Abri Suard, Krapina, Roc-de-Marsal and Scladina) are of MIS-5 age, two are of MIS-3 age (those from Couvin and Engis), and another, Cavallo-A, is, presumably, from a Mousterian level of unknown age underlying the site's Uluzzian deposit.…”

“…Subsequent to Benazzi et al's ( 2012 ) study, Le Cabec et al's ( 2013 ) analysis of anterior tooth root morphology and size also found a signifi cant overlap between Neandertals and early modern humans. In light of these fi ndings, of the problems encountered by Bailey et al ( 2009 ) with the Oase fossils, and of the contradictions in expert opinion about the affi nities of the teeth found in the Uluzzian levels of Cavallo, the conclusion is inescapable: for teeth from around the time of contact, secure classifi cation in terms of the taxonomic categories of Human Paleontology may be possible for large sets (e.g., the Grotte du Renne's) but not for isolated fi nds.…”

“…In a subsequent paper dealing with the crown and cervical outlines of deciduous lower second molars, Benazzi et al ( 2012 ) acknowledged this problem. Where the corresponding Lagar Velho tooth is concerned, they found it to be intermediate between Neandertals and modern humans in crown outline, and described this fi nding as corroborating the similar conclusion derived by Bayle et al ( 2010 ) from tissue proportions.…”

Comparison of maxillary first molar occlusal outlines of Neandertals from the Meuse River Basin of Belgium using elliptical Fourier analysis

“…With such small samples, the results may have been influenced by a few specimens. Furthermore, differential wear may affect occlusal and crown manual outlines (Benazzi et al 2012;Bailey et al 2016). Nevertheless, as has been shown by others, the Neandertals are distinct from Holocene humans in the shape of the post-canine teeth (Benazzi et al 2011a, b;2012;Bailey et al 2014;2016;Bauer et al 2016).…”

“…These are recorded as the amplitudes of the harmonics derived from four elliptical Fourier coefficients which describe subtle aspects of shape (Lestrel 1974;1997;Kuhl and Giardina 1982;Haines and Crampton 2000;Iwata and Ukai 2002). Contour analysis of human posterior teeth has been previously conducted on Neandertals and modern humans (Benazzi et al 2011a, b;2012;Bailey et al 2014;2016;Bauer et al 2016). Similar analyses have been conducted using elliptical Fourier functions to identify the degree of sexual dimorphism of human first molars (Ferrario et al 1999) and to tooth crown shape of the mandibular permanent distal premolar (P 4 ) of Neandertals (Bailey and Lynch 2005).…”