Neandertal-like traits visible in the internal structure of non-supranuchal fossae of some recent Homo sapiens: The problem of their identification in hominins and phylogenetic implications

Although recently the internal structure of the non-supranuchal fossa of Homo sapiens has been described and compared to that observed in the Neandertal suprainiac fossa, until now it has not been examined in any modern human children. In this study, the internal structure of this fossa in the occipital bones of three children (two aged 3‒4 years and one aged 5 years ± 16 months) and one adult individual representing recent Homo sapiens from Australia was analysed and compared to that of the Neandertal suprainiac fossa. In order to analyse the internal composition of the fossae of the examined specimens, initially, high-resolution micro-CT datasets were obtained for their occipital bones; next, 3D topographic maps of the variation in thickness of structural layers of the occipital bones were made and 2D virtual sections in the median region of these fossae were prepared. In the fossa of one immature individual, the thinning of the diploic layer characteristic of a Neandertal suprainiac fossa was firmly diagnosed. The other Neandertal-like trait, concerning the lack of substantial thinning of the external table of the bone in the region of the fossa, was established in two individuals (one child and one adult) due to the observation of an irregular pattern of the thickness of this table in the other specimens, suggesting the presence of an inflammatory process. Our study presents, for the first time, Neandertal-like traits (but not the whole set of features that justifies the autapomorphic status of the Neandertal supraniac fossa) in the internal structure of non-supranuchal fossae of some recent Homo sapiens. We discuss the phylogenetic implications of the results of our analysis and stress the reasons that use of the 3D topographic mapping method is important for the correct diagnosis of Neandertal traits of the internal structure of occipital fossae.