A medieval skull from northern Kyushu: 3D geometric morphometric insights into Japanese craniofacial variation.

The cranial morphology of the Japanese population has undergone notable diachronic changes from the Yayoi to the Modern period, reflecting both cultural and environmental influences. While substantial medieval skeletal series from Kamakura (eastern Japan) and Yamaguchi (western Honshu) have been analyzed, comparative material from northern Kyushu remains limited, particularly for well-preserved crania suitable for morphometric analysis. This study addresses this gap by applying three-dimensional geometric morphometrics to a well-preserved medieval skull (Kakihisa 1) excavated in Saga, northern Kyushu. Using Procrustes distances and principal component analysis with diachronic reference samples from the Yayoi, Kofun, Edo, and Modern periods, we describe the placement of Kakihisa 1 in cranial shape space and compare the cranial vault and facial skeleton separately. The cranial vault of Kakihisa 1 showed medieval-type dolichocephalic features and affinities with earlier reference distributions, whereas the facial skeleton plotted closer to the Edo distribution while retaining some affinity with earlier groups. These non-uniform affinities across cranial regions are compatible with the possibility that different cranial components followed partially decoupled diachronic trajectories, although the available evidence does not allow a definitive distinction between medieval specificity and regional continuity. We provide a landmark-based three-dimensional record of Kakihisa 1, including mirrored reconstruction to accommodate unilateral landmark loss, and situate the specimen within comparative diachronic reference samples. Although based on a single individual, Kakihisa 1 provides a useful comparative data point for medieval craniofacial variation in northern Kyushu and underscores the need for additional medieval specimens to evaluate temporal and regional patterns more robustly. Mini-abstract. Three-dimensional landmark analysis of a medieval skull from Saga, Japan indicates non-uniform vault and facial affinities, informing medieval craniofacial variation in northern Kyushu.