Phytoliths sample from a milling stone tool in Zone C (Piperno et al. 2000:895).
Piperno, D. R. 2009 Identifying crop plants with phytoliths (and starch grains) in Central and South America: A review and an update of the evidence. Quaternary International 193(1/2):146-159.
Piperno, D. R., A. J. Ranere, I. Holst and P. Hansell 2000 Starch Grains Reveal Early Root Crop Horticulture in the Panamanian Tropical Forest. Nature 407:894-897.