A geoarchaeological reassessment of the co-occurrence of the oldest Acheulean and Oldowan in a fluvial ecotone from lower middle Bed II (1.7ma) at Olduvai Gorge (Tanzania).

The coexistence of the oldest Acheulean and Oldowan industries means that the appearance of the former cannot be due to an anagenetic development from the latter. At Olduvai Gorge, Tanzania, both industries are found within the same chronostratigraphic unit, the Lower Augitic Sandstone (LAS; 1.7 Ma), at HWK, HWK-E, HWK-EE (Oldowan) and FLK-W and FLK-N (Acheulean). Recently, McHenry and Stanistreet (2018) and Stanistreet et al. (2018) have argued that the Acheulean site of FLK West is actually located within a more recent stratigraphic unit, the Middle Augitic Sandstone (MAS). If so, the Acheulean could potentially have evolved from the Oldowan anagenetically. We test this hypothesis by reviewing the stratigraphy of the LAS from the HWK area to the FLK-W site. Hay's (1976) previous work stresses the continuity of the LAS from HWK-EE to FLK-NN, and stratigraphic and sedimentological evidence indicates that while the MAS has eroded away, the LAS is continuous throughout the study area. According to Hay (1976), Uribelarrea et al. (2017) and this work, the LAS is present at HWK-EE, HWK-E, HWK, HWK-W, FLK-S, FLK-W, FLK-N and FLK-NN. The emergence of the Acheulean at Olduvai Gorge ca. 1.7Ma and its coexistence with the Oldowan thus demonstrates a cladogenetic, rather than an anagenetic, origin for the Acheulean. This has implications for the behavioral and biological interpretations of the origin and co-existence of both types of industries.