Survival of crinoid stems following decapitation: evidence from the Ordovician and palaeobiological implications

It was recently discovered that the stems of extant crinoids may survive af ter detachment of the crown, presumably feeding by the absorption of nutrie nts through the ectoderm. Previously, only one analogous, albeit morphologi cally dissimilar, pattern of crownless survival has been recognized from th e fossil record. Certain Upper Ordovician (Cincinnatian) crinoid pluricolum nals from Kentucky, Ohio and Indiana, derived from the disparids Cincinnati crinus spp., have rounded terminations reminiscent of some modern bourgueti crinid overgrowths. Such specimens have hitherto been interpreted as distal terminations of mature individuals that have become detached from their at tachment structures and taken to an eleutherozoic existence. However, it is considered more probable that they represent overgrowths of the column fol lowing predatory decapitation. If this new interpretation is correct, then post-decapitation survival of crinoid stems is now recognized for most of t he history of the crinoids, 'lethal' predation on crinoid crowns occurred a t least as early as the Late Ordovician and ancient crinoid populations can no longer be determined merely by counting crowns.