Bringing shape into focus: Assessing differences between blades and bladelets and their technological significance in 3D form

Laminar technologies have been adopted by Paleolithic foragers to produce a variate range of stone implements. Archaeologists have been capable of reconstructing the different reduction procedures involved in the production of laminar stone tools, often underlying a separation between the bigger blanks (i.e., blades) and smaller bladelets. However, these two blank types are in most cases poorly defined because their classification typically relies on arbitrary size thresholds that do not consider blank shape, which is a fundamental component of tool production and function. In this study, we investigate whether traditional classifications of blades and bladelets are meaningful in terms of morphology. For this purpose, we employ a three-dimensional geometric morphometric approach on a large sample of complete blanks retrieved from one of the earliest industries assigned to modern humans in southern Europe: the Protoaurignacian. We rely on a cutting edge protocol for acquiring virtual 3D meshes of stone tools using micro-computed tomography, which enables to scan large datasets of small-sized lithics. Our findings highlight distinct morphological tendencies across blank types that are in part triggered by the technological variability of the Protoaurignacian, including a shape component that significantly correlates with the three-dimensional size of the artifacts. Furthermore, we demonstrate the merits of combining 3D size and shape variables by running a discriminant function analysis that successfully classifies most artifacts into blades or bladelets. Overall, our results demonstrate that virtual analysis of stone tool form (both size and shape) can elucidate unknown aspects of lithic technology and its implications for human behavior in the past.