European Echinoderms Colloquium
Date: July 20-23, 2014
Place: University of Portsmouth, UK
PRESENTATIONS and ABSTRACTS
1) Baumiller, T.K., Syverson, V.J. and Gahn, F.J. Predation on Paleozoic crinoids: evidence from regenerating spines
Indirect evidence of predation in the geological past often comes in the form of features found among fossils inferred as anti-predatory. Spines represent one such feature. Spines are relatively common among Paleozoic crinoids, which were particularly vulnerable to predators, since as passive suspension feeders they had to remain exposed to currents and lacked the ability to locomote. If crinoid spines did indeed serve a defensive role they would do so either by deterring attacks entirely or by injuring the predator; in the latter case, some of the spines might also be injured. Given the exceptional regeneration abilities of crinoids, such injured spines would be expected to regrow following non-fatal encounters. The goals of this study were to (1) find regenerating crinoid spines as evidence of their defensive function, (2) obtain spine regeneration frequencies as a proxy of unsuccessful attacks, and (3) collect data on temporal patterns in spine occurrence among Paleozoic crinoids. Analysis of several hundred crinoid spines of the camerate crinoid, Gennaeocrinus, from a single Middle Devonian locality, revealed many regenerating spines. Instances of spine regeneration were also found among over one thousand spines belonging to the cladid pirasocrinids collected at several Pennsylvanian-age localities in Texas. However, the Devonian and Pennsylvanian samples contain many spines that were broken by post-mortem processes, making it difficult to accurately assess regeneration frequencies. We developed a maximum likelihood approach to estimate regeneration frequencies using all spine data; using this method, the results for both time intervals indicate that ~10% of the spines were regenerating. Given that this value represents a minimum estimate of predatory encounters, because neither fatal encounters nor fully regenerated spines are included in the metric, these data suggest that middle and late Paleozoic crinoids were under significant predation pressure. An analysis of genera described in the Treatise of Invertebrate Paleontology reveals that spinosity increased dramatically from the early to middle Paleozoic, reaching its peak among camerates in the Devonian, and only later among the cladids, which became the most diverse group in the late Paleozoic.