Predation, Resistance, and Escalation in Sessile Crinoids.

[摘要] As animal life diversified over the course of the Phanerozoic, the intensity of predator-prey interactions increased in several phases. Crinoids (Phylum Echinodermata: Class Crinoidea) were a dominant constituent of Paleozoic shallow marine faunas and constitute a lesser component of post-Paleozoic faunas; as most of them are sessile suspension feeders, they provide a good case study for the effect of increasing predation pressure on the Paleozoic evolutionary fauna. Herein are presented injury frequencies and examples of anti-predatory adaptations from a variety of modern and fossil crinoids, discussed with reference to those from previous studies. Rates of regenerating injuries in the modern sessile bathyal crinoid Holopus mikihe are shown to be comparable to those of shallow-water Mesozoic relatives and many Paleozoic taxa, and lower than any other measured injury rates in living crinoids. Regenerating injuries on disarticulated spines of Paleozoic crinoids similarly show an increase in regeneration frequency between the Paleozoic and Recent. Changes in arm branching morphology that increase resilience to predation are shown to have begun in the Early Paleozoic and reached their maximum by the Early Devonian; on this basis we infer that predators influenced crinoid evolution from the Ordovician, before the appearance of predatory vertebrates and echinoids known to prey on crinoids during later times. Beginning in the Devonian, snails parasitizing crinoids are associated with more frequent crinoid arm regeneration and with the presence of spines on the oral surface near their usual position, consistent with the hypothesis that the snails were targeted by predators with crinoids incurring collateral damage. Calyx spines were common in the Devonian and less common in the Mississippian, but tegmen spines associated with predation on parasitic snails persist up to the Late Mississippian. We also find indications that predation on crinoids decreased into the Permian. Our results support the hypothesis that escalation in the crinoid-predator relationship occurred during the Paleozoic during several different episodes of escalation related to new ecological developments. However, rather than a consistent upward trend in all types of defensive adaptations, we find that some defenses may be associated with types of hostile interaction that later lost ecological importance.

[发布机构] University of Michigan

[效力级别] crinoids

[关键词] predator-prey interactions;crinoids;paleoecology;Geology and Earth Sciences;Science;Geology