MISSISSIPPIAN PELMATOZOAN COMMUNITY REORGANIZATION - A PREDATION-MEDIATED FAUNAL CHANGE

Crinoid genera of the subclass Camerata generally dominated Late Silurian through Middle Mississippian pelmatozoan echinoderm assemblages. This dominance reached a peak during the early and middle Mississippian (Kinderhookian-Meramecian), but abruptly ended at the close of the Genevievian Stage (= lowermost Chesterian) in eastern North America. During the Genevievian Stage, crinoids of the subclass Inadunata became taxonomically more diverse but a few camerates, especially Platycrinites and Batocrinus, continued to be numerically dominant in many pelmatozoan assemblages. In eastern North America, platycrinids and batocrinids were reduced drastically near the Genevievian-Gasperian boundary. So obvious is this faunal change that, until recently, the Meramecian-Chesterian Series boundary was recognized as the last occurrence of Platycrinites penicillus. The sudden and drastic decline of numerically dominant platycrinids and batocrinids in eastern North America suggests a mass extinction, but is better interpreted as a range contraction and loss of dominance. Platycrinids, in particular, continued to be significant components of pelmatozoan assemblages in Europe and Asia long after the end of the Genevievian Stage. We infer that this reorganization of pelmatozoan assemblages in eastern North America was a product of predation, siliciclastic tolerance, and current-energy preference, with predation playing a major role. Reorganization resulted in post-Genevievian dominance by (1) cladid crinoids, (2) camerate crinoids that were cladid homeomorphs, and (3) the blastoid Pentremites. Foraminifera, conodonts, corals, brachiopods, bryozoans, and other echinoderm groups were affected little, if any, during this same time.