Xenocrinus baeri

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.

Below are photos of a limestone slab from the Upper Ordovician of southwestern Ohio with dozens of intact crinoids (heads attached to stems). This is a monospecific assemblage of the camerate crinoid Xenocrinus baeri (Meek, 1872) (Animalia, Echinodermata, Crinoidea, Monobathrida, Xenocrinidae). This fossil assemblage represents sudden burial of a crinoid thicket by a storm event. The limestone is channelform, and the surface facing the viewer is the underside (= base of channel).

Stratigraphy: Whitewater Formation, upper Richmondian Stage, upper Cincinnatian Series, upper Upper Ordovician.

Xenocrinus baeri (Meek, 1872) crinoids in fossiliferous limestone from the Whitewater Formation (upper Upper Ordovician) of Warren County, southwestern Ohio, USA.