Location, location, location: investigating perforation locations in Tritia gibbosula shells at Ksâr'Akil (Lebanon) using micro-CT data

Abstract

Perforated shells are often used to study socially mediated behavior in past hunter-gatherer groups. The assumption is that their exclusive symbolic function makes them ideally suited to investigate social networks, dispersal activity, and social interaction. Before making any statements regarding human behavior, however, it needs to be established whether perforated shells from archaeological assemblages were used as personal ornaments. One of the key issues regarding beach-collected marine taxa is whether beached specimens were purposefully collected, e.g., preferentially selected naturally holed specimens, or whether human-made perforations may be identified. Past studies have investigated these questions by comparing datasets from modern death assemblages of shells with archaeological collections and through manufacture and use-wear analysis (e.g., Bouzouggar et al. 2007; Vanhaeren et al. 2006) This study introduces a novel approach using μCT scans of pristine shells to create a threedimensional model of shell thickness in Tritia (Nassarius) gibbosula. This model is used to map robust and fragile zones on shells of this taxon. The goal of this approach is to identify structurally weak zones that would be prone to natural perforations. Heat maps of shell thickness are then used to investigate perforation locations in modern natural death and archaeological assemblages. Our results show that in natural death assemblages, most perforations occur in structurally weak zones, and that their distribution is random. In our archaeological samples, from early Upper Paleolithic contexts at Ksâr ‘Akil, (Lebanon), we found that perforations in T. gibbosula mainly occur in structurally weak zones, but their distribution within these zones is not random and favors locations facilitating easy suspension (e.g., on cordage). This suggests that at Ksâr ‘Akil, T. gibbolusa shells were used as beads, and that shells with conveniently located natural perforations were intentionally sought for, that humans perforated the shells themselves, or that they used a combination of both. This in turn, warrants investigations into the social and behavioral implications of these perforated beads. Further aspects of human involvement with the shells should be explored, for example, through use-wear analysis.