Oldowan - b) Olduvai BK spheroids, c. 1.8MYA;

Comment: Archaeological concensus is that spheroids are end-product of hammerstone use. On the other hand, some spheroids are too large to be usable hammerstones, suggesting non-utilitarian, aesthetic and 'symbolic' meaning.

Photo © Leakey, M. (1971). Olduvai Gorge, Vol. 3. Cambridge: At the University Press: pl. 24.