Krapina atlases suggest a high prevalence of anatomical variations in the first cervical vertebra of Neanderthals.

The first cervical vertebra, atlas, and its anatomical variants have been widely studied in Homo sapiens. However, in Neanderthals, the presence of anatomical variants of the atlas has been very little studied until very recently. Only the Neanderthal group from the El Sidrón site (Spain) has been analysed with regard to the anatomical variants of the atlas. A high prevalence of anatomical variants has been described in this sample, which points to low genetic diversity in this Neanderthal group. Even so, the high prevalence of anatomical variations detected in El Sidrón Neanderthal atlases needs to be confirmed by analysing more Neanderthal remains. In this context, we analysed the possible presence of anatomical variants in the three Neanderthal atlases recovered from the Krapina site (Croatia) within the Neanderthal lineage. Two of the three Krapina atlases presented anatomical variations. One atlas (Krapina 98) had an unclosed transverse foramen and the other (Krapina 99) presented a non-fused anterior atlas arch. Moreover, an extended review of the bibliography also showed these anatomical variations in other Middle and Upper Pleistocene hominins, leading us to hypothesise that anatomical variations of the atlas had a higher prevalence in extinct hominins than in modern humans.