Onychocrinus & Macrocrinus Crinoid Association - Indiana

This is a cool association of two different species of crinoids, Onychocrinus ulrichi & Macrocrinus mundulus. The quality of preparation on this fossil is exquisite - using skillful air-abrasion techniques under a stereo microscope.

It is believed that crinoids from the Ramp Creek Limestone were buried in sediment from nearby deltas during storms. The resulting siltstone deposits are soft enough that fossils can be extracted in exquisite, three-dimensional relief.

Crinoids are commonly known as sea lilies, though they are animals, not plants. They are echinoderms related to starfish, sea urchins, and brittle stars. They attached themselves to the sea floor and had feathery, tentacle-like appendages which they used to capture particles of food. First appearing in the Ordovician period, 488 million years ago, they still survive to this day in deep water.