Date Published: March 12, 2019
Publisher: Public Library of Science
Author(s): Wioletta Nowaczewska, Marcin Binkowski, Anna Maria Kubicka, Janusz Piontek, Antoine Balzeau, David Caramelli.
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.
The suprainiac fossa, a characteristic feature of Neandertals, was originally defined as a depression on the external surface of the occipital bone located above the inion (e.g. [1–3]). This Neandertal trait shows some degree of variation and is generally described as a transversely elongated structure, elliptical in shape, with a rough or pocked surface [4–6].
The occipital depressions observed in three examined immature specimens of recent Homo sapiens (R23, R24, and R82) do not co-occur with either strongly developed highest or superior nuchal lines or with the external occipital protuberance; thus they cannot be considered examples of supranuchal fossae. These superstructures are not completely formed at the early stages of ontogenetic development of the human occipital bone, and thus the presence of occipital depressions in these specimens cannot be considered to be related to their specific formation. These depressions were classified as the second type of occipital fossae identified to date in Homo sapiens, i.e. non-supranuchal fossae (see [12–14]). The occipital depression of adult specimen R4 was also classified as this type of fossa, based on its significant similarity in terms of external morphology to the suprainiac fossae of adult Neandertals (see also ). However, its shape is related to an arrangement of occipital superstructures which differs from that of Neandertals. It is also important to note that the size and shape of the area of the fossae examined in this study in immature specimens differ from those in Neandertal children (which exhibit larger and more elliptically-shaped suprainiac fossae) (for comparison see e.g. a Neandertal child—La Ferrassie 8; Fig 2, p. 41 in ). Additionally, in the R23 specimen we can observe a small elevation of the bone above the fossa, which is not characteristic of Neandertals.