Simakocrinus, Prokop, 2013

Prokop, Rudolf J., 2013, Simakocrinus Gen. Nov. (Crinoidea, Col.) From The Bohemian Early And Middle Devonian Of The Barrandian Area (The Czech Republic), Acta Musei Nationalis Pragae Series B 69 (1 - 2), pp. 65-68 : 65-66

Simakocrinus gen. nov. (col.)

T y p e s p e c i e s: Simakocrinus facilis sp. nov.,

Early Devonian, Pragian, Bohemia.

D e r i v a t i o n o m i n i s: In honour of Ing. Vladislav Šimák, my late friend and for many years standing collaborator of the Paleontological Department of the National Museum in Prague.

D i a g n o s i s. Stem homeomorphic bilateral, composed of minute but relatively hight columnals, roundedly trapezoidal to semielliptical in outline. Latera flat or slightly convex, mostly smooth; rarely with short, sporadicaly dislocated basal parts of cirri. Synarthry articulation. Articular facets plane, with a prominent fulcral ridge, created by two gently curved branches, i.e between the relatively narrow fine-grained inner ligamentary area and wide, coarse-grained outer ligamentary area. Lumen central, circular or semicircular formed by adjoining fulcral ribs accompanied by minute secondary axial canals.

C o m p a r i s o n. The columnals of the genus Simakocrinus gen. nov., (col.) resemble skeletal ossicles of some Silurian and Devonian myelodactylid crinoid genera especially Myelodactylus HALL, 1852 and Crinobrachiatus MOORE, 1962 . They differ from these genera in the prominent deep fulcral ridge, roundedly trapezoidal to semielliptical shape in transverse section, plane articular facet without distinct crenellae in the inner ligamentary area and most importantly, in the circular or semicircular lumen accompanied by minute secondary axial canals.

P a l e o e c o l o g y. Most skeletal remains of Simakocrinus gen. nov. (col.) were found in the washings from biosparitic and viz. biomicritic limestones which represent the arenaceous or clay marly sediments indicating that these minute crinoids lived on a soft sea bottom.

The crinoid living and anchoring strategy for soft bottom dwelling has been discussed by many authors, especially Springer 1926, Breimer 1978, Eckert and Brett 1985, Seilacher and McClintock 2005 and Donovan 2006.

The flexible stem and cirri are dislocated only lateraly and dorsally on columnals in the middle and proximal parts of stem, I assume that living simakocrinoids resembled a related myelodactylid species Crinobrachiatus brachiatus (Hall) from the Silurian of North America (see text-fig. 1 ).

R e m a r k s. Similar species to the genus Simakocrinus gen. nov. are known also from washings from weathered limestones from the other Pragian facies in the Barrandian Area, i.e. Koněprusy Limestone and Dvorce-Prokop Limestone. They were found also in the Kotýz Limestone (Lochkovian) and from the Middle Devonian Choteč Limestone of Eifelian age (see record of localities on p. xx.).

Figures

Text-fig. 1. Restoration of Crinobrachiatus brachiatus (HALL), a crinoid probably related to Simakocrinus, in semi-recumbent orientation. Cirri are depicted on one side of column only. Scale bar is 1 cm. (After Eckert and Brett, 1985).