Detailed Ordovician Pleurocystites Cystoid Fossil

Pleurocystites squamosus

Phylum Echinodermata, Class Cystoidea, Order Rhombifera

Geological Time: Middle Ordovician

Size: Pleurocystites Cystoid is 30 mm long overall; Theca: 20 mm by 15 mm; Matrix: 80 mm by 60 mm.

Fossil Site: Galena Formation, Goodhue County, Minnesota, USA

Code: AW80

Price: $125

Description: This plate displays an example of the rhombiferan cystoid known as Pleurocystites. 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. This one must have been buried soon after death to be preserved in such a near complete state.

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