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Revision of the flexible crinoid genus Ammonicrinus and a new hypothesis on its life mode

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Bohaty J.

Acta Palaeontologica Polonica

2011

tom 56

nr 3

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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1 Acta Palaeontologica Polonica

1 Bohaty J.

1 2011

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Revision of the flexible crinoid genus Ammonicrinus and a new hypothesis on its life mode