File:Ectenocrinus simplex fossil crinoids (Kope Formation, Upper Ordovician; Petersburg, Kentucky, USA) 5.jpg

English: Ectenocrinus simplex (Hall, 1847) - fossil crinoids in fossiliferous limestone from the Ordovician of Kentucky, USA. (CMC IP 38442, Cincinnati Museum of Natural History & Science, Cincinnati Museum Center, Cincinnati, Ohio, USA)

Crinoids (sea lilies) are sessile, benthic, filter-feeding, stalked echinoderms that are relatively common in the marine fossil record. Crinoids are also a living group, but are relatively uncommon in modern oceans. A crinoid is essentially a starfish-on-a-stick. The stick, or stem, is composed of numerous stacked columnals, like small poker chips. Stems and individual columnals are the most commonly encountered crinoid fossils in the field. Intact, fossilized crinoid heads (crowns, calices, cups) are unusual. Why? Upon death, the crinoid body starts disintegrating very rapidly. The soft tissues holding the skeletal pieces together decay and the skeleton falls apart.

The rock shown above is the underside of a fossiliferous limestone bed from the Upper Ordovician of Kentucky. The long structures are stretches of articulated crinoid stems. The brush-like structures are intact crinoid heads of Ectenocrinus simplex. Notice the overall oriented nature of the stems and crowns - they were likely rolled on the seafloor by storm currents before final burial. The presence of multiple, articulated crinoid heads indicates rapid burial - a thicket of Ectenocrinus crinoids on an ancient, relatively shallow seafloor was knocked down by a storm event and buried. Limestone beds that represent storm events are called tempestites.

Classification: Animalia, Echinodermata, Crinoidea, Disparida, Homocrinidaee

Stratigraphy: Kope Formation, Edenian Stage, lower Cincinnatian Series, lower Upper Ordovician

Locality: Petersburg, northwestern Boone County, far-northern Kentucky, USA

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See info. at:

en.wikipedia.org/wiki/Crinoid