Unfused transverse foramen of the atlas vertebra in the Neandertal lineage fossils

In anatomically modern humans, the atlas can display an unfused transverse foramen (UTF) but currently the presence of UTF in the Neandertal lineage is uncertain due to a scarcity of prevalence studies and no exhaustive record of its presence throughout the entire hominin fossil record. In this context, this study aimed to assess the UTF prevalence in Neandertal lineage fossils. In the Neandertal lineage fossil record, UTF was identified in three atlases: a Middle Pleistocene Preneandertal fossil (VC3) from Sima de los Huesos, and the Neandertal specimens Kebara 2 and Krapina 98. These results suggest that UTF may have been present in the hominin lineage since, at least, the Middle Pleistocene. An UTF could have been present in other, older hominin lineages but this remains unclear due to the generally poor preservation of atlases outside the Neandertal lineage fossil record. However, the existence of UTFs in the Neandertal lineage warrants further investigation into the evolutionary and developmental factors underlying this vertebral morphological variation.