Environmental and Taxonomic Control of Growth, Morphology, Taphonomy, and Sediment Production in Living Stalked Crinoids (Echinodermata)

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9628215 Messing Stalked crinoids represent a major component of living assemblages and contribute substantially to modern skeletal sediments along the western flank of the Little Bahama Bank. Three aspects of stalked crinoid biology and taphonomy are examined in order to better understand the processes and rates of production, and post-mortem modifications of modern crinoidal sediments, as follows: 1) How do growth rates among different species and within species vary at different depths and under different environmental conditions? Growth rates are measured directly via proven methods of tagging and recovery that permit in situ maintenance of specimens. 2) To what extent do depth and environmental conditions control crinoid morphology? Many features currently applied to crinoid species diagnoses and phylogenetic hypotheses vary ontogenetically, ecophenotypically, geographically and/or bathymetrically. Clear understanding and recognition of crinoid species are critical to biostratigraphic analyses and paleoecological reconstruction and hypothesis-testing. Application of previously successful tag-and-recovery experiments will permit specimens to be transplanted to different habitats and depths. 3) How do morphological and ecological variations among and within taxa affect taphonomic processes such as patterns of stalk disarticulation, skeletal sediment production rates, and the nature of skeletal grains contributed to sediments, and how can this information be applied to reconstruction of fossil assemblages? A combination of anatomic and petrographic thin sections and scanning electron microscopy of living and experimentally decomposed crinoid stalks, and skeletal grains retrieved from sediments are used to examine ligament anatomy, the pattern of ligament decay and the development of cements relative to increasing stalk degradation. The study organisms have a fossil record dating to the Triassic. As such, these modern assemblages represent an excellent analogue for better understan ding paleoecological processes and interpreting ancient crinoidal deposits. The aspects of crinoid ecology and taphonomy proposed for study are thoroughly interconnected and represent a logical extension of the successful research program carried out under prior NSF funding at previously established study sites.