Differentiating potential of “archaic traits” on permanent upper second molars: from Homo erectus to Homo altaiensis

To reveal the extent of introgression of archaic features into the modern human's dentition, we analyzed the distribution of nine dental non-metric features on permanent upper second molars of the pre-sapient population of Eurasia. Previously, it was argued that five of these traits, which are usually attributed to the so-called "archaic markers" (epicrista, posterior fovea, crista obliqua, trapezoid crown shape, additional odontoglyphic elements) are more characteristic to the ancient representatives of the genus Homo than to modern H. sapiens. We also analyzed the distribution of the frequency of hypocone reduction and three additional tubercles - parastyle, Carabelli trait and additional distal cusp (C5). The data on samples of H. erectus, H. ergaster/erectus/ georgicus, H. antecessor, European Middle Pleistocene Homo, Chinese hominins of the Middle and Late Pleistocene, Neanderthals, and Denisovans were analyzed by the PCA method using taxonomic status of samples as the grouping variable. The results of the analysis reveal that the frequencies of the studied traits are unevenly distributed within the genus Homo. While one trait, namely a crista obliqua is present with high frequency in all groups, the other characteristics reveal different distribution patterns. It is shown that in the Early and Middle Pleistocene, the epicrista (transverse crest) is localized in the Caucasus and the Iberian Peninsula only. The parastyle is found only in Denisovan specimens. The Middle Pleistocene population of Europe is characterized by reduced frequencies of archaic traits, a simplified odontoglyphic pattern, and an increased frequency of hypocone reduction. According to the results of the principal component analysis, the distribution of most of the analyzed dental characteristics is statistically consistent with the taxonomic differentiation of the compared groups and their chronological position.