Are Homo sapiens nonsupranuchal fossa and Neanderthal suprainiac fossa convergent traits?

Abstract

The autapomorphic status of the Neanderthal suprainiac fossa was recently confirmed. This was a result of a detailed analysis of the internal bone composition in the area of the suprainiac depression on Neanderthal and Homo sapiens specimens. However, while anatomical differences between Neanderthal suprainiac fossa and the depression in the inion region of the occipital bone of fossil and recent Homo sapiens have been discussed in detail, the etiology of these structures has not been resolved. In this article, the hypothesis that the Homo sapiens non-supranuchal fossa and the Neanderthal suprainiac fossa both formed to maintain the optimal shape of the occipital plane (to minimize strain on the posterior cranial vault) is tested. First, the variation in the expression of the fossa above inion in the crania of recent Homo sapiens from European, African, and Australian samples was examined, and the degree of structural similarity between these depressions and the Neanderthal suprainiac fossa was assessed. Next, the relationship between the shape of the occipital squama in the midsagittal plane and two particular features (the degree of the occipital torus development and the occurrence of a depression in the inion region that is not the supranuchal fossa) were analyzed. Based on the results, it is suggested that the Homo sapiens non-supranuchal fossa and Neanderthal suprainiac fossa are convergent traits.