[Nebullis]

I think the question isn't how so many could exist, they were, afterall, a very successful species, but how they could have disappeared so rapidly. The concentration of fossils is attributed to rapid drying, not flooding, of sea-waters during ice-ages, resulting in the Ordovician extinction.

[viaveritasvita]

"The concentration of fossils is attributed to rapid drying, not flooding, of sea-waters during ice-ages, resulting in the Ordovician extinction."

An interesting theory. I'll be most curious to read Austin's paper.