Not a biologist, but OTOH they might have had a very different body structure that doesn't conserve well, e.g. like molluscs. Or maybe we _did__ find their rem

Not a biologist, but OTOH they might have had a very different body structure that doesn't conserve well, e.g. like molluscs. Or maybe we _did__ find their remains and just have no idea they were part of an intelligent civilization. I mean, that's not a question any respectable researcher would be inclined to raise in the paper about the discovery...