Wouldn’t you just love to know what the prehistoric Jomon toilet was like?
Studies show (yes, somebody studies things like that) that the Jomon people went regularly to (and their housedogs were toilet-trained as well to) poop, more properly, to defecate onto a shell midden. The shell middens, which were basically their kitchen dumps, were located outside their dwellings or a short walk away. After the grand business was finished, they covered up their mess with more shells.
What happened then was that calcium seeped out of the shells and permeated the excrement(poop). The excrement then hardened and turned into a stone-like state. You know how poop usually has a sort of ice cream shape, and scientists call that ice-cream-shaped excrement – coprolites. The coprolites naturally stuck to the shells maintaining their original shape.
As it turns out, this was a very satisfactory arrangement as it left the area around Jomon homes sanitary and unpolluted, so the people only had insects and weeds to contend with. Studies also show that the roundworm didn’t appear until after the Jomon era ended and until the Yayoi people who came later had changed the Jomon toilet arrangements.
Heritage of Japan 