Neurocranial shape variation among Tarascan populations: Evidence for varying degrees in artificially modified crania in pre-Hispanic West Mexico (1200-1400 AD).

Introduction: Along the Mesoamerican western margin, the Zacapu basin has yielded a large number of human remains demonstrating usage of artificial cranial modification (ACM). However, at the onset of the Middle Postclassic (1200-1400 AD) only few individuals still exhibit clear signs of ACM. Some authors have suggested that, rather than disappearing entirely, ACM may have become less visible anatomically, making it difficult to identify based on simple visual analyses. Here, we used 3D geometric morphometric methods to investigate the extent to which ACM persisted during the Postclassic in this region.

Materials And Methods: We measured the 3D vault's shape changes in a sample of surface-scanned human crania: 55 individuals from the Postclassic Zacapu basin and a control group of 31 individuals from a Huichol Mexican Indian sample and a French medieval series from La Granède. We used a principal component analysis to explore the shape variation within the sample and employed the neighbor joining method to identify morphological groups. Finally, we quantified each individual's asymmetry.

Results: We identified three groups displaying shape features diverging from those of the control group. The first group is characterized by marked fronto-obelionic ACM, whereas the other two show mild forms of ACM. The individuals in all three groups display moderate to high degrees of asymmetry compared to the control group.

Discussion: The marked fronto-obelionic modification is clear evidence of a specific ACM technique. The two types of mild ACM most likely result from different techniques but their moderate degree of modification brings into question the intentions behind their production.