Platycrinites & Macrocrinus Crinoid Association - Illinois

About Crawfordsville Crinoid Fossils

Crinoids from the Ramp Creek Limestone of Crawfordsville, Indiana are world-famous for their extraordinary preservation and diversity. During the Mississippian Period, sudden storm events likely swept fine sediment from nearby deltas across the seafloor, rapidly burying living crinoids where they stood. This quick entombment protected even the most delicate structures, resulting in soft siltstone that can be carefully prepared to reveal fossils in stunning, fully three-dimensional relief.

The Crawfordsville area preserves one of the most important crinoid assemblages ever discovered, with hundreds of described species ranging from common forms to bizarre and highly specialized morphologies. Many specimens retain complete crowns, arms, stems, and even fine pinnules—details that are rarely preserved elsewhere. Because of this exceptional quality, Crawfordsville crinoids have played a major role in the scientific study of crinoid anatomy, evolution, and paleoecology.

Crinoids, often called “sea lilies,” are animals rather than plants and belong to the echinoderms, a group that includes starfish, sea urchins, and brittle stars. Like their relatives, crinoids exhibit radial symmetry, tube feet, a water vascular system, and body parts arranged in multiples of five. Crinoids first appeared in the Ordovician Period, nearly 488 million years ago, and while most of the elaborate stalked forms seen at Crawfordsville are long extinct, a small number of crinoid species still inhabit modern oceans today.