Revision of the Flexible Crinoid Genus Ammonicrinus and a New Hypothesis on Its Life Mode

  • Bohatý J
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Abstract

The lecanocrinid Ammonicrinus (Flexibilia) is newly interpreted based on new material from the Middle Devonian of the Rhenish Massif (Eifel and Bergisches Land, Germany). The species have echinoid-like tubercles on the attachment and on the column, which bear articulated spines. The intraspecific variability of the column is discussed for three facies-controlled morphotypes, herein classified as standard ``exposed-{''} or ``encased roller-type{''} and the rare ``settler-type{''}. New specimens have floating transitions between different plate sculpturing and between those individuals with none or one to several columnals with herein termed ``lateral columnal enclosure extensions{''} on the proximal-most, barrel-like dististele and the following mesistele, which is solely distinguished by these extensions. Based on this interpretation, Ammonicrinus kongieli is evaluated as a subjective junior synonym of Ammonicrinus sulcatus. The latter species was first recognised from the Eifel (Germany). ``Ammonicrinus wachtbergensis{''}, from the upper Eifelian of the Eifel, is declared a subjective junior synonym of Ammonicrinus doliiformis. The first nearly complete specimen of Ammonicrinus kerdreoletensis is described from the lower Eifelian of Vireux-Molhain (southern Ardennes, France). Two new species are described: Ammonicrinus jankei sp. nov. and Ammonicrinus leunisseni sp. nov. A functional morphologic trend in perfecting the crown encasement by continuous modification of the lateral columnal enclosure extensions of the mesistele from the Eifelian to the Givetian, indicates a vagile benthic ``predator{''}-driven evolution of ammonicrinids in the Eifel area. Several ammonicrinid species are herein defined as spined soft-bottom dwellers, feeding in low-intensity current water, possibly through a self-produced water flow. The first known postmortem encrusting epizoans on ammonicrinid endoskeletons are reported.

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Bohatý, J. (2010). Revision of the Flexible Crinoid Genus Ammonicrinus and a New Hypothesis on Its Life Mode . Acta Palaeontologica Polonica, 56(3), 615–639. https://doi.org/10.4202/app.2010.0020

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