What does the trigonid crest pattern tell us on the Arago dental sample?

Nowadays, one of the most important issues in human evolution is to try to understand the complex evolutionary scenario in Europe during the Middle Pleistocene (MP). The remarkable morphological variability that characterizes the MP species suggests that the settlement of Europe could be the result of several migration waves, at different times, coming from the same mother population probably placed in Southwest Asia. The human fossils found in the Caune de l’Arago (Tautavel, France) are, together with the Sima de los Huesos hominins, one of the largest and best documented samples of European MP (1). To date, this site has yielded more than 140 human remains that, according to the latest dates obtained for the Arago hominin-bearing layers (2), are nearly contemporaneous with the Sima de los Huesos population. For that purpose, these fossils are of special interest to investigate human evolution in Europe during this period. Since dental morphology is an important source of taxonomic and phylogenetic information (3), the pattern of the trigonid crest has proved to be useful to characterize the Neanderthal species (4). Therefore, we have analyzed the trigonid crest pattern exhibited at the outer enamel surface (OES) and enamel dentine junction (EDJ) of the Arago lower molars using a microtomographic technique. Furthermore, to understand the polarity of this morphological feature in the evolution of European populations, we also compared this morphological trait among Homo antecessor, the Sima de los Huesos population, Homo neanderthalensis and Homo sapiens. Our results reveal that the Arago specimens present high frequencies of continuous mid-trigonid crests, typical of the Neanderthal lineage. However, the height of their crest and their variability at the dentine are lower, although this may be due to the small sample size. Despite the similar chronology and the geographical proximity of Arago and Sima de los Huesos sites, our data support the idea that the Arago dental sample exhibits Neanderthal patterns together with other plesiomorphic features, while the Sima de los Huesos teeth are more like Homo neanderthalensis. These results are consistent with those recently published by Bermúdez de Castro and coworkers (5) that proposed a less linear settlement of Europe where two or more hominin groups could have coexisted during the MP.