Growth patterns and evolutionary trends of Devonian crinoid columns |
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| Institution: | 1. Key Laboratory of Orogenic Belt and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China;2. ARC Centre of Excellence in Ore Deposits (CODES), University of Tasmania, Private Bag 79, Hobart 7001, Australia;3. School of Resources and Environmental Engineering, Hefei University of Technology, Hefei 230009, China;4. Department of Sciences and Technology, The Inner Mongolia Autonomous Region, Hohhot 010010, China;1. Division of Paleontology, American Museum of Natural History, Central Park West at 79th St., New York, NY 10024, USA;2. Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, P.O. Box 37012, MRC 121, Washington, D.C. 20013-7012, USA;3. School of Earth Sciences, The Ohio State University, 125 South Oval Mall, Columbus, OH 43210, USA |
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| Abstract: | The general morphology of the crinoid column is briefly reviewed; growth patterns deduced from the study of stem fragments and dissociated columnals are analysed in the two commonest groups occurring in the Devonian strata of France: the Cyclici and the Pentameri. Problems concerning the introduction of new columnals beneath the calyx and the differentiation of cycles in the proximal part of heteromorphic stems are set. Evolutionary trends affecting various morphological elements include size increase, ornamentation development, cirri insertion and distribution, epifacet regression and formation of composite and secondary holdfasts. At present, these trends appear to be limited to small systematic units but proxistelisation, defined as the downward extension of proxistele characters to the other stem regions, seems to be wide-spread in the Pentameri. The difficulty in determining the evolutionary process (neoteny, progenesis…) due to the lack of information on early ontogenetic stages is emphasized. |
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