ORDOVICIAN CRINOID FAUNAS FROM OHIO (PHYLUM ECHINODERMATA)

The Middle and Upper Ordovician strata in the Ohio-Indiana-Kentucky tri-state region are well known for crinoid faunas, yet these faunas have generally been viewed, at least informally, as a depauperate crinoid fauna. Is this true? Face-value global data on Ordovician through Llandovery crinoid faunas are evaluated to address this question.

The Cincinnatian (Edenian through Richmondian) of the tri-state region are correlative elsewhere with strata ranging in age from the middle Caradoc (Marshbrookian) through the Ashgillian (Rawtheyan). More than 39 valid species (assigned to 20 genera) are currently reported from the Cincinnatian. The generic assignments are viewed as robust, but a few species could become junior synonyms after systematic revision. The species and genus richness distribution through this stratigraphic interval is bimodal, with peaks in the Correyville and Waynesville formations (8 genera and 13 species; 11 genera and 15 species, respectively). Faunas from both of these formations are from the Ashgill, and their richnesses are within or exceed a single standard deviation of the mean for all other Ashgill faunas known globally. For other Ashgill crinoid faunas with more than one species reported, the genus richness mean is 6.1 (SD=4.8), and the species richness mean is 6.8 (SD=6.8). Relative to the other known Ashgill crinoid faunas the Correyville and Waynesville faunas are not depauperate.

However, Correyville, Waynesville, and other Cincinnatian faunas are depauperate if compared to older and younger faunas. The end-Ordovician event significantly affected the record of crinoid faunas. The genus and species richness of Ordovician through Llandovery crinoid faunas has a bimodal distribution with richness peaks during the Caradoc and the Telychian, thus relative to Caradoc and Telychian crinoid faunas, Ashgill, Rhuddanian, and Aeronian (as a whole) faunas are depauperate. This trend is exaggerated if all pelmatozoan echinoderms are considered.