A REVIEW AND REASSESSMENT OF PREDATION-DRIVEN EVOLUTIONARY TRENDS IN CRINOIDS IN LIGHT OF NEW DATA ON PALEOZOIC PREDATION INTENSITIES

Predation has been argued as a major driving force of evolutionary innovation and morphological change among many taxa and crinoids are no exception. Trends of increasing plate thickness and spinosity among Paleozoic crinoids, onshore-offshore diversity patterns of post-Paleozoic stalked crinoids, origination of autotomy (shedding) planes in the stalk and arms of articulates, crawling and swimming abilities, choice of semicryptic habitats and nocturnal-diurnal behavior among comatulids, and planktonic and pseudoplanktonic life styles have all been attributed to predation pressure. To evaluate the supposed predation-driven trends in crinoids, we review the patterns, the evidence of predation among extant crinoids, and predation evidence from the fossil record.

In modern settings, direct evidence of predation on crinoids is sparse, consisting of a few reports of fish-comatulid interactions and a single report of an echinoid-isocrinid interaction. More easily accessible, though slightly more difficult to interpret, have been indirect data, such as arm regeneration frequencies among comatulids and isocrinids and crinoid-rich gut contents of supposed predators.

Compared to neontological data on crinoid predation, which, although sparse, indicate that crinoids today are attacked, the fossil record of predation has been largely anecdotal and inconclusive. No direct evidence has been reported, and indirect evidence consists of a few post-Paleozoic examples of arm regeneration, crinoid-rich fecal pellets, and regenerated arms and spines. No systematic attempt to gather predation data for Paleozoic crinoids has been reported. Here, we provide two preliminary examples of regeneration frequencies in the arms and spines of Mississippian crinoids that suggest that Paleozoic predation intensities on these animals may have been moderately high. These data suggest that predation-driven morphological and behavioral trends in crinoids may be expected, and that the fossil record contains information relevant to testing such evolutionary scenarios.