A geometric morphometric analysis of hominin upper first molar shape

Abstract

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 tax onomic assignment. In this study, we have applied geometric morphometric methods to explore the morphological variability of the upper first molar (Ml) across the human fossil record. Our emphasis focuses on the study of the phenetic relationships among the European middle Pleis tocene populations (designated as H. heidelhergensis) 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.

Geometric morphometric analysis of the crown morphology of the lower first premolar of hominins, with special attention to Pleistocene Homo

“…This may reflect a mor phological particularity of this biological population as its marked reduction of the size of their posterior teeth (Bermudez de Castro and Nicolas, 1995). The similarities in P3 shape, along with other dental traits (Bermudez de Castro, 1987, 1988Martinon Torres, 2006;Martinon-Torres et al, 2006;Gomez-Robles et al, 2007), support the hypothesis that there is a close phylogenetic relationship between the hominins of Atapuerca-Sima de los…”

“…The tips of the main cusps were visually located in the images while simultaneously examin ing the fossil or cast. The cusp tip was assumed to be in the center of the wear facet in those teeth where wear had removed it (Bailey, 2004;Martinon-Torres et al, 2006;Gomez-Robles et al, 2007 Bookstein, 1991) that were later removed.…”

“…Al though we have kept the assignment to H erectus proposed by Weidenreich (1937) Although the H neanderthalensis and H heidelbergensis distri butions overlap, the Sima de los Huesos first premolars plot at the extreme of PC1. In general, H heidelbergensis from Sima de los Huesos and H neanderthalensis have been described as having similar dental traits, the only difference being that H nean derthalensis presents higher degrees of expression for some of those traits (e.g., Bermudez de Castro, 1987, 1988Martinon To rres, 2006;Martinon-Torres et al, 2006;Gomez-Robles et al, 2007). It is interesting to note that, in this particular tooth, Sima de los Huesos specimens display a morphology that is even more pronounced than the classic Neandertals.…”

“…Recent publications have addressed the dental morphological differences among fossil hominins (Bailey, 2004;Bailey and Lynch, 2005;Martinon-Torres et aL, 2006;Gomez-Robles et al, 2007), continuing a tradition that began with the examination of the occlusal morphology of earlier African Pliocene and Pleistocene hominin taxa (Wood and Abbot, 1983;Wood and Uytterschaut, 1987;Wood and Engleman, 1988).…”

Dental evidence on the hominin dispersals during the Pleistocene

“…In addition, the posterior dentitions of Eurasians groups include a typical combination (although not for all specimens) of a deep anterior fovea with continuous midtrigonid crest, and transverse crest in the lower premolars typical of NEA and HEI (14,20), but also ascertained in ANT and ERE in variable percentages (14,15,18). In addition, the particular morphology of the upper first molar (14,21) and lower fourth premolar (20) in ANT, HEI, SH, and NEA emphasizes the links between the Early and Middle Pleistocene populations in Europe (SI Fig. 6).…”