TAXONOMIC RE-EVALUATION OF FOSSIL CRINOIDS FROM THE BOBCAYGEON AND VERULAM FORMATIONS (UPPER ORDOVICIAN) NEAR BRECHIN, ONTARIO

The Ordovician is a key interval for understanding the evolutionary history and diversification of crinoids (Echinodermata, Crinoidea) because nearly all major clades first appear in Ordovician strata. After their initial diversification during the Early Ordovician, crinoids subsequently underwent a taxonomic and morphologic radiation coincident with the Great Ordovician Biodiversification Event (GOBE) and reached peak Ordovician diversity during the Sandbian. Following the GOBE, crinoid taxonomic diversity dramatically declined during the end-Ordovician mass extinction.

The Upper Ordovician (lower Katian) Bobcaygeon and Verulam Formations near Brechin, Ontario are comprised of a highly diverse, well-preserved crinoid fauna. These “Brechin Fauna” crinoids are preserved alongside a rich Late Ordovician echinoderm community including representative ophiuroids, paracrinoids, cystoids, edrioasteroids, edrioblastoids, cyclocystoids, and homalozoans. This fauna provides an exceptional window into a taxonomically diverse Late Ordovician crinoid community from the interval between the Sandbian diversity peak and the end-Ordovician extinction. Although the sedimentology, stratigraphy and paleoecology of these Upper Ordovician strata have been studied in detail, the Brechin Fauna crinoids have not had a comprehensive taxonomic evaluation since Frank Springer’s (1911) classic monograph.

A survey of newly collected material from the Bobcaygeon and Verulam Formations reveals a large number of exceptionally preserved crinoid specimens with arms, stems, and attachment structures intact. Because many of these taxa were previously described based on incomplete material, this new collection provides an opportunity to more fully describe morphologic details of known Ordovician crinoid taxa and to conduct a taxonomic re-evaluation. An initial survey of the new material indicates nearly uniform taxonomic diversity among cladids (seven genera), camerates (eight genera), and disparids (seven genera) with lower generic diversity for flexibles (one genus) and hybocrinids (one genus). Our preliminary investigation also suggests several new, currently undescribed, taxa may also reside in the collection.