INSIGHTS INTO THE TAXONOMY AND PALEOECOLOGY OF THE ‘BEAD BED' CRINOID (ECHINODERMATA: CRINOIDEA) BASED ON NEW MATERIAL FROM THE LOWER SILURIAN BRASSFIELD FORMATION OF EAST-CENTRAL KENTUCKY

Abstract

The lower Silurian Brassfield Formation crops out throughout eastern midcontinent North America as a prominent carbonate deposit representing a variety of shoal to shallow shelf environments. The upper portion of this unit throughout Ohio and Kentucky is characterized by the exceptional abundance of distinctive crinoid columnals historically referred to as ‘beads'. Although recognized for more than a century, the taxonomic identity of the crinoid responsible for producing these elements remains unknown; this is due largely to the taphonomic state of ‘beads', which are nearly always preserved as isolated ossicles not commonly discovered as articulated segments and never in direct association with identifiable calyx plates or arm segments. Recently discovered material from east-central Kentucky allows these columnals to be confidently attributed to the morphogenus Floricolumnus (col.) Donovan and Clark. These elements are now recognized as components of a coiled dististelar attachment structure. There is also an association between ‘beads' and crown material, namely small, uniserial, pinnulate brachials. Collectively, this material supports the interpretation that the producer of these columnals was a large diplobathrid camerate, almost certainly a dimerocrinitid.