The bedrock in your area should be Cretaceous, but that coral bearing  rock sure looks Paleozoic to me.  It may perhaps be a glacial erratic – a piece of rock scraped up by an ice sheet during their advance, which is then left behind when the ice melts and retreats.

Thanks for the information. The roughly equivalent Formation here in my area would be the Pella Fm, which is Chesterian.  The Pella has lots of great stuff in it, but nothing that reminds me of those fabulous productids of yours, that’s for sure.

There must have been shell banks of those things in your area for you to find so many slabs full of…[Read more]

Echinoconchus are quite large and occur is some abundance in the Keokuk Formation in my neck of the woods (Midwest USA). I believe the time frame on that Fm is late Osagean, but I may be off a Stage.  Still, that should be similar in age to your stuff.  Index Fossils of N America states that spines are present on both valves of Echinoconchus, b…[Read more]

What part of South Dakota was this found in? It does look like a coral, probably a Paleozoic one to my eye.  Was this near the Black Hills area?

Any chance those might be Echinoconchus sp?

A great list!  I’d be happy to try and help with cephalopods, and would have a general knowledge of Iowa Paleozoic fossils, especially Ordovician and Devonian.