CRINOIDS AS PREY AND PREDATORS: DIVERSE EVIDENCE FROM THE FOSSIL RECORD AND RECENT (Invited Presentation)

Until relatively recently, it was a widespread myth that crinoids were not subject to common predation, but studies of boreholes and arm regeneration have shown that they are, indeed, good to eat. Again, why did some ancient crinoids develop such obvious anti-predatory defenses, like thorny stems and cups? Lane postulated that the large anal sacs and tubes of at least some Paleozoic crinoids may have housed the gonads, which were thus a target for predators. Decapitated crinoids are known from the Late Ordovician, Triassic and Recent, and are probably the result of predatory cephalopods or fishes eating the crown. Scavenging or predation by benthic molluscs on crinoids dates back to the Late Ordovician. Arm autotomy is widely recognized as an anti-predatory defense; autotomy within the stem or beneath the crown may have been important in Paleozoic clades as in the post-Paleozoic isocrinines. For example, Springer (1926, Proc. USNM) remarked on a large collection (30+ specimens) of headless individuals of the Silurian myelodactylid Crinobrachiatus brachiatus (Hall) that were otherwise well preserved.

But perhaps some ancient crinoids were predators, not prey. Grimmer & Holland (1990, Acta Zool., fig. 5) noted “partly digested remains of some relatively large prey items” in the rectum of extant Holopus rangii d’Orbigny, presumably trapped by the enrolled, abutting arms. Similar arms are not unknown in the Paleozoic in, for example, many flexibles.