Morphometric analysis of molars in a Middle Pleistocene population shows a mosaic of ‘modern’ and Neanderthal features

Authors

  • María Martinón-Torres,

    Corresponding author
    • National Research Center on Human Evolution (CENIEH), Burgos, Spain
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  • Petra Spěváčková,

    1. Department of Anthropology (Anthropology of Past Populations), University of West Bohemia, Pilsen, Czech Republic
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  • Ana Gracia-Téllez,

    1. Depto. de Geografía y Geología (Área de Paleontología), Facultad de Ciencias, Universidad de Alcalá, Alcalá de Henares, Spain
    2. Centro Mixto UCM-ISCIII de Investigación sobre Evolución y Comportamiento Humanos, Madrid, Spain
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  • Ignacio Martínez,

    1. Depto. de Geografía y Geología (Área de Paleontología), Facultad de Ciencias, Universidad de Alcalá, Alcalá de Henares, Spain
    2. Centro Mixto UCM-ISCIII de Investigación sobre Evolución y Comportamiento Humanos, Madrid, Spain
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  • Emiliano Bruner,

    1. National Research Center on Human Evolution (CENIEH), Burgos, Spain
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  • Juan Luis Arsuaga,

    1. Centro Mixto UCM-ISCIII de Investigación sobre Evolución y Comportamiento Humanos, Madrid, Spain
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  • José María Bermúdez de Castro

    1. National Research Center on Human Evolution (CENIEH), Burgos, Spain
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Correspondence

María Martinón-Torres, National Research Center on Human Evolution (CENIEH), Paseo Sierra de Atapuerca s/n, 09002 Burgos, Spain. E: maria.martinon.torres@gmail.com

Abstract

Previous studies of upper first molar (M1) crown shape have shown significant differences between Homo sapiens and Homo neanderthalensis that were already present in the European Middle Pleistocene populations, including the large dental sample from Atapuerca-Sima de los Huesos (SH). Analysis of other M1 features such as the total crown base area, cusp proportions, cusp angles and occlusal polygon have confirmed the differences between both lineages, becoming a useful tool for the taxonomic assignment of isolated teeth from Late Pleistocene sites. However, until now the pattern of expression of these variables has not been known for the SH sample. This fossil sample, the largest collection from the European Middle Pleistocene, is generally interpreted as being from the direct ancestors of Neanderthals, and thus is a reference sample for assessing the origin of the Neanderthal morphologies. Surprisingly, our study reveals that SH M1s present a unique mosaic of H. neanderthalensis and H. sapiens features. Regarding the cusp angles and the relative occlusal polygon area, SH matches the H. neanderthalensis pattern. However, regarding the total crown base area and relative cusps size, SH M1s are similar to H. sapiens, with a small crown area, a strong hypocone reduction and a protocone enlargement, although the protocone expansion in SH is significantly larger than in any other group studied. The SH dental sample calls into question the uniqueness of some so-called modern traits. Our study also sounds a note of caution on the use of M1 occlusal morphology for the alpha taxonomy of isolated M1s.

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