A geometric morphometric analysis of hominin upper first molar

Centro Nacional de Investigación sobre Evolución Humana (CENIEH), Avda. de la Paz, 28, 09006 Burgos, Spain.
Journal of Human Evolution (Impact Factor: 3.73). 10/2007; 53(3):272-85. DOI: 10.1016/j.jhevol.2007.02.002
Source: PubMed


Recent studies have revealed interesting differences in upper first molar morphology across the hominin fossil record, particularly significant between H. sapiens and H. neanderthalensis. Usually these analyses have been performed by means of classic morphometric methods, including the measurement of relative cusp areas or the angles defined between cusps. Although these studies have provided valuable information for the morphological characterization of some hominin species, we believe that the analysis of this particular tooth could be more conclusive for taxonomic assignment. In this study, we have applied geometric morphometric methods to explore the morphological variability of the upper first molar (M(1)) across the human fossil record. Our emphasis focuses on the study of the phenetic relationships among the European middle Pleistocene populations (designated as H. heidelbergensis) with H. neanderthalensis and H. sapiens, but the inclusion of Australopithecus and early Homo specimens has helped us to assess the polarity of the observed traits. H. neanderthalensis presents a unique morphology characterized by a relatively distal displacement of the lingual cusps and protrusion in the external outline of a large and bulging hypocone. This morphology can be found in a less pronounced degree in the European early and middle Pleistocene populations, and reaches its maximum expression with the H. neanderthalensis lineage. In contrast, modern humans retain the primitive morphology with a square occlusal polygon associated with a round external outline.

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    • "Detailed information on methods in GM can be found in numerous sources [Bookstein, 1989, 1991; Richtsmeier et al., 2002; Adams et al., 2004; Zelditch et al., 2004; Slice, 2007; Mitteroecker and Gunz, 2009]. The contribution of GM to phylogenetic studies depends on the correlation of shape variability with taxonomic affinities [Bailey, 2004; Macholán, 2006; Gómez-Robles et al., 2007; Astúa, 2009; White, 2009]. To date, most GM dental analyses of occlusal crown surfaces have focused on the Hominidae [Martinón-Torres et al., 2006; Gómez-Robles, 2007, 2008], and only a few have examined cercopithecoids . "
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    • "Shape information is extracted by removing any translational or rotational differences and then scaling to a best fit. Several authors emphasize the ability of geometric morphometric techniques to assess morphological differences precisely and have recommended the use of three-dimensional (3D) tools, avoiding possible complications derived from the analysis of 2D images (Gómez-Robles et al., 2007, 2008). GMM analyses the relative positions of anatomical landmarks used to approximate the outlines and surfaces of the tested object. "
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    • "However, these methods are less practical for quantifying tooth shape, as they require micro-CT data that are costly and time-consuming to collect, limiting the sampling potential. Two-dimensional morphometrics has been successfully used to examine occlusal morphology in hominins (G omez-Robles, 2008; Gomez-Robles et al., 2007), rodents (Macholan, 2006; Renaud, 1999), and primates (White, 2009), and has been found to provide more shape information than simple linear measures (Bernal, 2007). Twodimensional photographs of the lingual aspect of the tooth were deemed most appropriate for our analysis for several reasons: (1) the majority of shape variation in the taxa sampled occurs in this plane (roughly parasagittal); (2) the lateral aspect of the tooth is relatively flat, thus allowing repeatable positioning of the tooth for imaging; and (3) several homologous landmarks were identifiable on the lingual surfaces of these teeth. "
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