Diagnostic differences in mandibular P4 shape between neandertals and anatomically modern humans

This study uses elliptical Fourier analysis to quantify shape differences observed in the P₄ crown of Neandertals and anatomically modern humans. Previously, P₄ shape was assessed qualitatively, and results suggested marked differences between Neandertals and anatomically modern humans (Bailey [2002] New Anat. 269:148-156). The goal of this study was to investigate the P₄ shape in more detail, quantifying it in order to determine its utility for taxonomic classification and phylogenetic analysis. A comparison of mean shapes confirms that the mesiolingual portion of the P₄ is truncated in Neandertals, and that this produces a distinctively asymmetrical P₄. A randomization test confirms that the shape difference between Neandertals and anatomically modern humans is significant. Principal component and discriminant function analyses indicate that the relative size of the lingual portion of the tooth also affects tooth shape, with the lingual portion of the Neandertal P₄ being narrower than that of anatomically modern humans. Classification of P₄ crown shapes using discriminant functions analysis is far from perfect. While 86.4% of the teeth were correctly classified, classification was much better for anatomically modern humans (98.1%) than it was for Neandertals (65%). Fortunately, crown shape is but one of several diagnostic characters of the P₄ crown. P₄ crown asymmetry can be added to the growing list of dental morphological characters distinguishing Neandertals from anatomically modern humans. Moreover, based on a comparison of mean tooth shapes in fossil and recent humans, symmetry, rather than asymmetry, appears to be the primitive state, and the high frequency of P₄ asymmetry is likely derived in Neandertals.