Found in Sully Co SD on a field border. Picture 2 has a men’s size 7 boot next to it for size reference. Picture 3 (image 3727) is a close-up of part of the item. It is possible to go get additional pictures of the item soon as snow is mostly gone if more detail is needed. Thank you all!
Hi Gail! Thanks for the heads up. Cool specimen, but I suspect it’s a limestone concretion of some sort. Not a vertebrate specimen unfortunately, so no mosasaurs yet! LOL! The weird weathering pattern on the surface suggests there are fossils in it. Looks like corals again or possibly crinoids. Paleozoic most likely… brought in by the glaciers. I’d be interested in hearing the opinions of everyone else though!
Looks solid enough to remove and at least see what is on the other side. If you do decide to move it, please post some more pics. Gotta love a good mystery!
PS: I attached a more detailed SD geologic map for your records just in case you didn’t have it yet.
If its Paleozoic, there are few possibilities for the age. It could be Mississippian (Early Carboniferous) limestone, similar to the one which makes up Wind Cave in the Black Hills, much farther west. But more likely I think it could be the Cambrian Deadwood Formation, which is most common in the Black Hills, but is found as far northeast as North Dakota and Manitoba. However if these are echinoderms, I think that they are much more likley middle Palezoic crinoids, than Cambrian eocrinoids or cystoids. The most likley possibility is that if its Palezoic and echinoderm, than its probably Orodvician, a small remainder of the Pleistocene glacier carving.