Camerate Crinoid and Blastoid Association Plate
from the Burlington Formation

Description: Well-preserved examples of a Camerate crinoid of the Family Actinocrinitidae accompanied by a spiraculate blastoid, a close relative of the crinoids. The Burlington Formation is as much as 50 m in thickness, and covers a large portion of Missouri as well as Iowa and Illinois along the Mississippi River. It is composed largely of undolomitzied crinoidal limestone. The sediment was an unconsolidated, coarse-grained, and poorly sorted sand to gravel substratum which was episodically mobile. Such a substrate was not suitable for brachiopods, bryozoans, or corals, but was apparently ideal for the many types of camerate crinoids that have been found. While the material was episodically disturbed by storms, the rigidly sutured calyx of camerate crinoids were ideally suited to preservation. Few are found with attached arms or stems, but many parts are also found with the crowns in the “hash” that was preserved. It was also a suitable home for blastoids; indeed, some 20% of the known fossil blastoid taxa are known from the Burlington Formation. Here are 2 of the diverse forms preserved in this wonderful deposit, with the white crowns a stark contrast to the orange-brown matrix. There are other crinoid fragments to be seen as well, making a fine showcase of the materials found.