Paleobiologic and taphonomic aspects of the "granulosa" trilobite cluster,Kope Formation (Upper Ordovician, Cincinnati Region)

A new, low-density trilobite body cluster from an Upper Ordovician Kope For mation mudstone in the Cincinnati region is characterized by well-preserved , articulated specimens. This cluster is polytaxic, size-segregated, and sh ows an unusual variety of flexure postures in the most common taxon, Flexic alymene aff. granulosa. Specimens show internal pyritization and associated pyrite-filled tubular burrows, and were preserved by rapid deposition of m ud from a sediment-laden flow. Size-segregation among species, but size-con sistency within species, coupled with sedimentological data and apparently haphazard body orientation data, suggest that the trilobites represent a bi ological association, rather than the product of mechanical sorting. While the majority of specimens are inverted, many are dorsal-up, and some are in clined to bedding. Postures include prone (i.e., nonflexed), simple dorsal or ventral flexure, and complex stances that combine both dorsal and ventra l flexure. Flexure pattern appears largely unrelated to sediment compaction . We interpret the cluster as an association of live trilobites that were e ntombed in situ. Specimens may have inverted prior to burial as a behaviora l posture, or as a response to onset of burial. The animals were likely pre served in the process of escaping, as they tried to free themselves from be ing buried. This is in contrast to the tightly enrolled stance in some tril obites, especially other Flexicalymene, commonly associated with rapid buri al events, and indicates a new behavioral aspect of trilobite paleobiology. The distribution of associated burrows suggests that the rotting carcasses attracted scavengers.