Triassic brittlestar beds of Poland: a case of Aspiduriella ludeni (v.HAGENOW, 1846) and Arenorbis squamosus (E. PICARD, 1858)

Abstract

Exemplified by a new occurrence site of mass-aggregated Aspiduriella ludeni (v.HAGENOW, 1846) from the Lower Muschelkalk (lowest Anisian) sequence of the Holy Cross Mountains, Central Poland, discussed are life conditions of ophiuroids in that region of the Muschelkalk Basin (Middle Triassic) in Central Europe. Postulated is their fast deposition (burial) by the rip-current transport of alive, possibly torpid, and/or newly dead specimens captured by stormy agitation from their shallow subtidal and/or intertidal habitats. The palaeogeographical setting of the Holy Cross region is compared to that of the Silesia region in southern Poland, highly influenced till the early-Middle Triassic by oceanic waters of the Tethyan Realm. Shortly reviewed and/or discussed are the formerly known ophiuroid occurrences in Silesia, to be supplemented by a mass-aggregated case of Arenorbis squamosus (E. PICARD, 1858). Commented are also other ophiuroid aggregations reported from the Muschelkalk Basin, and whose occurrence is considered in terms of their environmental conditions controlled both by physical (fluctuation of water parameters, and its dynamics) and biotic (low predation stress) agents. A biogeographical significance of the genus Aspiduriella during Triassic is outlined, to suggest its Muschelkalk-refugee provenance in the late Middle and Late Triassic of the Tethyan Realm.