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19 hours ago · Chasmataspis, a horseshoe crab-like chasmataspid arthropod: Winneshiek Shale. 460 Ma Decorah, Iowa. A Middle Ordovician site confined to a large impact Crater that is known for exceptionally exquisite preservation of conodonts, bivalved arthropods, and the earliest eurypterids in the fossil record. Pentecopterus, the oldest known eurypterid
