Identifying intentional flake production at the dawn of technology: A technological and 3D geometric morphometric study

The production of sharp-edged stone flakes is often viewed as a unique adaptation specific to the hominin lineage. The discovery of large stone cores and flakes dated to 3.3 Ma has shown that the earliest evidence of hominin stone flake production differs from the later Oldowan (dated to 2.6 Ma) record. Recent discoveries have shown that capuchin monkeys (Sapajus libidinosus) can unintentionally produce sharp-edged flake assemblages as a by-product of percussive behaviour. Capuchin monkeys are the only wild primate to intentionally strike two stones together (stone-on-stone percussion) to produce quartz powder. In doing so, they unintentionally produce high frequencies of sharp-edged flakes. It has been suggested that these possess the same technological attributes commonly used to describe intentional hominin stone flakes. Here we directly compare the basic morphometric descriptions, technological and 3D morphometric properties of unintentional capuchin flakes with experimentally produced flakes derived from two intentional flaking techniques employed during the Plio-Pleistocene, freehand and passive hammer knapping and a sample of Oldowan freehand flakes from Olduvai Gorge (Tanzania). Our results show that unintentional stone-on-stone flakes overlap in terms of their shape, size and technological attributes with those produced through intentional knapping techniques. We, however, identify attributes that may be critical for differentiating between intentional knapping techniques documented in the early archaeological record and unintentional flakes. Using these data we show that Oldowan flakes more closely resemble intentional freehand techniques.