What?!? This is FASCINATING. I become increasingly intrigued by the Pre-Columbian history of the Americas. Like the following passage -- doesn't it seem to describe not just these societies in the Amazon, but nearly every society that was present when Europeans arrived, from Iroquois to Incas?
"Little is known about the culture practiced by the people in these mound villages. But preliminary research suggests that this culture's ceramics were 'cruder' than those of the culture that preceded them, known as the Geoglyphs, who lived in that region from about 400 B.C. to A.D. 950." (from the livescience article)