Characterization of Neandertal cranial shape using the method of thin-plate splines.

Abstract

This study applies a new morphometric technique, the method of thin-plate splines (Bookstein, 1991) to the problem of describing and quantifying cranial shape in European and Near Eastern Neandertals. This method begins with a geometry that includes all information that could be gained from ratios of linear measurements or angles measured using the same landmark set. Shape difference is modelled as a Cartesian deformation and decomposed by its partial warps, yielding multiple geometrically orthogonal components of shape difference. I compared European and Near Eastern Neandertal cranial shape to recent Norwegian, Australian, Eskimo, Ugandan, and Polynesian samples, as well as to prehistoric samples from the French Mesolithic and European Upper Paleolithic periods. I also included the Middle Pleistocene crania Petralona and Broken Hill, usually attributed either to Homo erectus or early archaic Homo sapiens. Twenty landmarks were digitized from photographs or scale drawings of crania in norma lateralis. The mean landmark locations for each sample were calculated to a glabella-inion baseline using shape coordinates. The Norwegian mean is the reference form to which all other mean forms and individuals were compared. Results show that the Neandertals do not differ significantly from more recent humans in 14 of the 18 features defined by the partial warp analysis. In the four features where the Neandertals differ, there is overlap with the post-Neandertal human samples in every case. No autapomorphic features of lateral cranial shape were found for the Neandertals. For two warps, the Neandertals share the more modern state, whereas Petralona and Broken Hill are similar to one another and different from the later samples. The La Chapelle cranium differs from the other Neandertals in important ways and should not be used to typify Neandertal craniofacial morphology. Evidently, Neandertals are not as different from more modern humans as is commonly reported. Neandertal autapomorphies proposed in the literature are examined, and previous characterizations of Neandertal facial form are discussed in the light of these results.