An Upper Second Molar from Akhshtyrskaya Cave and Population Affinities of the Middle Paleolithic Hominins of the Caucasus

The Akhshtyrskaya cave site in northwestern Caucasus dates mostly to the Middle Paleolithic. In 1961, during the analysis of faunal assemblage from layer 3a, a permanent upper second molar of Homo (AKH 1) was discovered. Initially, it was attributed to fossil Homo sapiens. Here, we present new findings related to this specimen, specifically to its external and internal morphology, amount of enamel and dentine in the lateral part of its crown, and a comparison of metric and nonmetric characteristics with those of Denisovans, H. ergaster/erectus/georgicus, H. erectus, H. antecessor, H. neanderthalensis, H. sapiens, Middle Pleistocene Homo of Europe, and Middle and Late Pleistocene Homo of China, distinct from H. erectus. At the first stage, frequencies of nonmetric traits were subjected to principal component analysis. At the second stage, obtained PCA scores were integrated with measurements of the same specimens using PC analysis with grouping variable. Results suggest that the molar from Akhshtyrskaya by no means belongs to H. sapiens. Its morphology is very archaic, linking it to mostly Middle Pleistocene hominin teeth from China. The volume of lateral dentine opposes AKH 1 to molars of Late Pleistocene Homo of Europe and those of H. sapiens, revealing a shift toward Denisovans. The specimen likely belongs to an evolutionary line that has thus far not been found in Europe. Probably, it is of Asian origin.