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Wisconsin State Fossil

Trilobite (Calymene celebra); photo by Jim Brace-Thompson / American Federation of Mineralogical Societies (all rights reserved; used by permission). 

Official State Fossil of Wisconsin

Wisconsin designated the trilobite (Calymene celebra) as official state fossil in 1985. Related to modern day crabs, lobsters, shrimp, spiders, and insects, this extinct marine arthropod flourished in shallow prehistoric salt waters during the early to middle Paleozoic age. All State Fossils

Like modern arthropods, they had to periodically molt their shells to grow, so one trilobite could have left a dozen or more shed carapaces to fossilize.