Pycnocrinus dyeri (fossil crinoids) (Arnheim Formation, Upper Ordovician; Dent, Ohio, USA) 3 – Detroit Picture

Pycnocrinus dyeri (fossil crinoids) (Arnheim Formation, Upper Ordovician; Dent, Ohio, USA) 3

Pycnocrinus dyeri (Meek, 1872) – fossil crinoids from the Ordovician of Ohio, USA. (Department of Geology collection, Wayne State University, Detroit, Michigan, USA)

This remarkable crinoid plate is from the famous Cincinnatian Series of the tristate area of Ohio-Kentucky-Indiana. Rocks in the Cincinnatian were deposited in relatively shallow marine facies during the Late Ordovician. The Cincinnatian succession is mostly interbedded limestones and shales. Most of the limestones are event beds (= tempestites), deposited during ancient storms.

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), such as the examples seen here, 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.

Classification: Animalia, Echinodermata, Crinoidea, Camerata, Monobathrida, Glyptocrinidae

Stratigraphy: Arnheim Formation, lower Richmondian Stage, upper Cincinnatian Series, upper Upper Ordovician

Locality: unrecorded/undisclosed site at or near the town of Dent, Cincinnati urban area, Hamilton County, southwestern Ohio, USA
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See info. at:
en.wikipedia.org/wiki/Crinoid

Image published by James St. John on 2018-07-06 19:58:17 and used under Creative Commons license.

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