The hominin teeth from the late Middle Pleistocene Hualongdong site, China

Between 2014 and 2015, abundant human fossils dated to about 300 ka were found in the Hualongdong (HLD) site, Anhui province, South China. The HLD human sample consists of a nearly complete skull with 14 teeth in situ, one partial maxilla with one premolar in situ, six isolated teeth, three femoral diaphyseal sections, and a few cranial pieces. Former studies found that the HLD hominins show a mosaic of primitive and derived characteristics with regard to the Homo clade. While the cranium, limbs, and mandible display predominantly primitive features shared with early Homo specimens, the facial bones display closer affinities to modern humans. To assess the phylogenetic affinities of the HLD taxa and other Asian hominin record as well as African and European Pleistocene specimens, we present a comparative morphometric analysis of the 21 HLD teeth. Our dental study reveals a mosaic of primitive and derived dental features for the HLD hominins regarding the Homo clade. The results show that most of the HLD dental features resemble those of Late Pleistocene hominins expect for the robust roots of premolars and molars that approach Middle Pleistocene morphologies. A few features like the reduced M₃ link the HLD 6 mandible with East Asian Pleistocene hominins and recent modern humans. The HLD also lacks typical Neanderthal traits. This population presents a remarkable number of derived dental features not present in most Middle Pleistocene hominin fossil assemblages in East Asia with perhaps the exception of Panxian Dadong or Jinniushan. The findings from HLD teeth provide further support to the diversity in late Middle Pleistocene hominin evolution. Several scenarios can potentially explain this variability and would need further exploration. Hualongdong-particular morphology could be the result of genetic drift or gene flow with a more archaic form, such as Homo erectus. Alternatively, the HLD sample could belong to a hominin population closely related to the Homo sapiens clade and be distinct from H. erectus, Neanderthals, and Denisovans.