Novy nalez temer kompletniho jedince morske hvezdice z ceske svrchni kridy

The occurrence of asteroids in the Bohemian Cretaceous Basin is very limited. Their truly abundant occurrence is known only from the Upper Cenomanian and Lower Turonian strata of the so-called surf facies (e.g., the localities of Skalka near Velim, Kamajka, etc.). However, without exception, these occurrences (together with other fauna) consist only of isolated elements accumulated after the complete disintegration of the asteroid skeletons. The principal factor limiting the preservation of asteroid is their complicated skeleton consisting of many articulated elements. The muscular and ligamentary articulations between them decompose easily, which causes complete post-mortem destruction of the skeletons. Therefore, more complete individuals of asteroids are rare, and their preservation necessitates specific conditions. A nearly complete specimen has recently been found at Radouč locality in the town of Mladá Boleslav in Central Bohemia. The rock exposure is formed by medium-grained calcareous sandstone passing upwards to coarse-grained calcareous sandstone of the uppermost part of the Jizera Formation (apparently the Mytiloides labiatoidiformis inoceramid zone and the Subprionocyclus neptuni ammonite zone of the Upper Turonian). These levels correspond lithostratigraphically to the lower part of the Teplice Formation in the western part of the Bohemian Cretaceous Basin. The asteroid individual is rather well preserved. However, the detailed surface sculpture of the marginal parts seems to be damaged, probably by dissolution during diagenesis of the sediments. The preservation of the overall shape of the skeleton of the individual indicates its rapid post-mortem burial, probably with the dorsal side facing upwards. Only the distal parts of 2 arms have rapidly disintegrated at the site of its final deposition (Figs. 3a–c). The individual reaches the size of approximately 9 cm in the radial–interradial direction. It has relatively long and narrow arms with more than half of the supramarginal parts of each arm in dorsal contact. At the same time, there is a corresponding reduction in the disc size. The arrangement and the character of small disc elements are strongly disturbed by post-mortem decay. In conclusion, taxonomic determination of the find as Nymphaster sp. (Family Goniasteridae) can be tentatively considered. To refine it, richer material is needed. The described asteroid is deposited in the collections of the Chlupáč Museum, Faculty of Science, Charles University, Prague, No. CHMHZ MS 2892.

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