Comparative analysis of the glabellar region morphology of the late Pleistocene Minatogawa crania: a three-dimensional approach

The Late Pleistocene human fossils recovered from the Minatogawa fissure in Okinawa Island are important in understanding the population history of the Japan archipelago. Based on high-resolution laser scanning, we conducted a three-dimensional (3-D) topographic evaluation of the glabellar and superciliary regions of the Minatogawa and Jomon crania. We aimed to address the question of whether the glabellar morphology of the Minatogawa crania can be seen as a possible ancestral condition of the Jomon people, or whether it more likely represents a distinct morphological pattern. In addition to comparative descriptions and evaluations of the visualized topography, we conducted principal components and cluster analyses using a data set of approximately 240 points located within a confined glabellofrontal area. Results indicate that the male Minatogawa I exhibits a distinct rhomboid to ovoid glabellosuperciliary prominence, in the form of an undifferentiated swollen structure that encompasses both glabellar and superciliary arch regions. Unlike the Jomon condition, this leads to a lack of concave inferolateral contour of the prominence and the virtually complete obliteration of bilateral superciliary expression. The Minatogawa II and IV female crania also exhibit the same morphological pattern at weaker levels. On the other hand, absolute glabellar projection of Minatogawa I is not as great as the developed Jomon examples. This indicates that it is the pattern that is distinctive of Minatogawa, rather than glabellar prominence itself.