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Abstract
Two specimens of crinoid columnals with previously undocumented lumen morphologies are described from Silurian (Wenlock) strata of the Cincinnati Arch region, eastern-midcontinent North America. An attachment structure with a prominent tetralobate lumen, the first tetralobate lumen in a columnal reported from the Silurian, was recovered from a microbioherm in the Massie Formation of southeastern Indiana. An isolated columnal ossicle with a large hexalobate lumen, the first hexalobate lumen-bearing columnal documented, was recovered from a skeletal dolowackestone in the Lilley Formation of southwestern Ohio. These discoveries significantly increase the disparity of the otherwise morphologically conservative Silurian crinoid-columnal fauna.
Acknowledgements
Funding for this study was provided by a Dry Dredgers Paul Sanders Grant awarded to JRT. The owners and management of the New Point Stone quarry at Napoleon graciously allowed access to the tetralobate lumen-bearing holdfast locality. Earlier drafts of this article were improved by discussions with Carlton E. Brett (University of Cincinnati) and the constructive reviews provided by William I. Ausich (Ohio State University) and Fiona E. Fearnhead (Birkbeck College, University of London). This is a contribution to the International Geoscience Programme (IGCP) Project No. 591 – The Early to Middle Paleozoic Revolution.