It has been argued that increases in predation over geological time should result in increases in defensive adaptations in prey taxa. Recent in situ and laboratory observations indicate that cidaroid sea urchins feed on live stalked crinoids, leaving distinct bite marks on their skeletal elements. Similar bite marks on fossil crinoids from Poland strongly suggest that these animals have been subject to echinoid predation since the Triassic. Following their near-demise during the end-Permian extinction, crinoids underwent a major evolutionary radiation during the Middle-Late Triassic that produced distinct morphological and behavioral novelties, particularly motile taxa that contrasted strongly with the predominantly sessile Paleozoic crinoid faunas. We suggest that the appearance and subsequent evolutionary success of motile crinoids were related to benthic predation by post-Paleozoic echinoids with their stronger and more active feeding apparatus and that, in the case of crinoids, the predation-driven Mesozoic marine revolution started earlier than in other groups, perhaps soon after the endPermian extinction.macroecology | macroevolution | predation | escalation | cidaroids P redator-prey interactions may represent a significant driving force of evolutionary change (1-4), but predation and its consequences are often difficult to assess in Recent communities and even more so in the fossil record. Data on fossil and extant crinoids, commonly known as sea lilies and feather stars (Echinodermata), indicate that they suffer from predation by fishes, and numerous evolutionary trends have been ascribed to such interactions (5-15). Among these are (i) crawling and swimming abilities in comatulids (6), (ii) choice of semicryptic habits and nocturnal-diurnal behavior among comatulids (6), (iii) increasing plate thickness and spinosity among Paleozoic crinoids (9), (iv) offshore displacement of late Mesozoic/Cenozoic stalked crinoids (11), and (v) origin of autotomy (shedding) planes in the stalk and arms (13). Some of these trends have served as examples of dramatic change in marine ecosystems, such as the Mesozoic marine revolution (MMR) (2, 16) and the middle-Paleozoic marine revolution (9).Although predation by fish has received the most attention, crinoids may be the prey of other organisms, most notably benthic invertebrates. Until recently, few data hinted at the importance of benthic predators to crinoids, including a swimming response in a comatulid when perturbed by the predatory sea star Pycnopodia helianthoides (17), the presence of crinoid pinnulars in the gut of the goniasterid Plinthaster dentatus (18), and a crinoid arm observed in the claw of the crab Oregonia gracilis (17). Recently, submersible studies of stalked crinoids belonging to the Isocrinidae have revealed that they are prey to cidaroids, or pencil urchins. Evidence for this interaction includes (i) in situ observations of cidaroids among large aggregations of motile isocrinid sea lilies (Neocrinus decorus and Endoxocrinus parrae), (ii) proximi...
