[SunkenCiv]

I noticed that the text says "at least seven types... were edible" and that a number of the rest were extinct (meaning that there's no way to know for sure that they were edible). In any case, perhaps they ate the edible kinds, and used the others for something else, such as dyes, apparel, or decoration.

[Fedora]

What I'm wondering is how they got from shellfish to the conclusion that this was a civilization comparable to Mesopotamia's? The only indication of civilization I see in the article is the ziggurat mentioned in the last sentence, but that alone doesn't seem to justify the claim of the headline.