File:Onychocrinus exculptus fossil crinoid (Edwardsville Formation, Lower Mississippian; Crawfordsville area, Montgomery County, Indiana, USA) (17204172290).jpg

Onychocrinus exculptus Lyon & Casseday, 1860 - fossil crinoid from the Mississippian of Indiana, USA. (William Morgan collection)

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.

This is an articulated crown of Platycrinus saffordi from the famous Crawfordsville crinoid fauna in Indiana. The deposit is well known for its abundance of exceptionally preserved, articulated fossil crinoids and other echinoderms. This crinoid occurrence is one of the most spectacular on Earth - it contains at least 63 different crinoid species (Ausich, 1999), many of which are quite sizable.

Classification: Animalia, Echinodermata, Crinoidea, Flexibilia, Taxocrinida, Synerocrinidae

Stratigraphy: Edwardsville Formation, Osagean Stage, upper Lower Mississippian

Locality: near Crawfordsville, Montgomery County, western Indiana, USA

Reference cited:

Ausich, W.I. 1999. Lower Mississippian Edwardsville Formation at Crawfordsville, Indiana, USA. pp. 145-154 in Fossil Crinoids. Cambridge, U.K. Cambridge University Press.

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