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Little Barren River, Sulphur Well Historic District, Kentucky

  Crinoids are marine invertebrates that resemble flowers with clusters of waving arms atop a long stem. They are exclusively marine creatures and belong to the same family as starfish and sand dollars. Their presence in rock and sediment indicates an ancient marine environment. In fact, these fossils date to about 450 million years ago when warm tropical seas covered what is now Kentucky and much of the north-central US.

  Pieces of crinoids are abundant in this sample and show great variation in their morphology. The ribbed rod (lower left) is a stem; the rings are stem or stalk segments. Rings can be round or pentagonal star-shaped; some are perforated in their center.

  Many of the smaller grains are limestone—compacted limey mud from the ancient seas.

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