Crinoid Ecological Morphology

Recent studies of crinoids reveal that their connective tissue, known to be mutable, is also contractile, and that certain stalked taxa are capable of crawling and subject to predation by cidaroid sea urchin. Aspects of crinoid functional morphology, ecology, and paleobiology are reviewed in the context of these findings. Mutability and contractility of ligament are important to autotomy, posture maintenance, and motility, and those, in turn, are shown to play a role in how crinoids acquire nutrients, select habitats and respond to predation pressure. A review of predation on crinoids supports the view that it is ecologically significant. Motility, a trait critical for handling predation pressure by stalkless crinoids, is shown to play an analogous role in stalked crinoids. The distribution of traits required for motility among extant and fossil crinoids reveals that their frequency increased dramatically following the Permo-Triassic extinction, with low values characterizing the Paleozoic and high values characterizing the post-Paleozoic.