Unusual Cystoids Death Assemblage

Pleurocystites sp.

Phylum Echinodermata, Class Cystoidea, Order Rhombifera

Geological Time: Middle Ordovician

Size: Cystoid fossils are 52 mm to 95 mm long

Fossil Site: Sugar River Formation, Trenton Group, Sackets Harbor, New York

Pleurocystites CystoidsDescription: This plate displays a death assemblage of no less than SEVEN rhombiferan cystoids known as Pleurocystites. Two are seen in dorsal aspect, while the remaining five are preserved ventrally. Cystoids are relatives of the crinoids that have oval rather than rounded calyces. They were either stalkless or attached to a stalk much like crinoids. Their triangular pores distinguish them from all other echinoderms. They arose during the Late Cambrian and became extinct during the Late Devonian (~500-375 million years ago). Like all other echinoderms they typically would disarticulate shortly after death. These must have been quickly buried to allow them to be preserved as you see them here.

click crinoid pictures to enlarge

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