Paleospolecenstva hadic (ostnokozci) ze stramberske spodni kridy

Early Cretaceous brittle stars (ophiuroids) have not been systematically studied in the territory of the Czech Republic yet. The studied fauna comes from three thick limestone bodies in the immediate proximity of the town of Štramberk. Most localities with ophiuroid finds (Fig. 1) belong to the Kopřivnice Formation of Late Valanginian age (sensu Houša 1976) in the Kotouč Quarry (localities 6, 20 and 25), in the Obecní Quarry (locality 3) and in the lower Blücher Quarry (locality 1). Locality 2 in the Obecní Quarry pertains to the Hradiště Formation according to Svobodová et al. (2011), being of Hauterivian and Barremian age.

The herein preliminarily described material was gathered from old rock samples, tentative old rock washings and sets of Štramberk Early Cretaceous fossils collected and studied in the 1960s–1980s. During many years of research, only three hundred disarticulated skeletal elements of brittle stars have been found here. They are therefore extremely rare in the Štramberk area.

Several assemblages of ophiuroid ossicles from the Kopřivnice Formation contain only arm vertebrae. As suggested by the wide morphological variety of the vertebrae, the presence of many species now lacking a closer systematic classification can be expected here. However, the assemblage from the Hradiště Formation (Obecní Quarry, locality 2) contains taxonomically important lateral arm plates, which enabled the study of ophuiroid diversity. Here, the dominant genera are Ophiotitanos (Ophiodermatina) and Squamophis? (Euryalidae). On the other hand, taxa Ophiomusa sp. (Ophiomusaidae), Dermocoma sp. (Ophiodermatina) and Ophiacanthina fam. et gen. indet. are rare. As concerns the drawings by Mauric Remeš (1902), it is evident that his specimens were only two fragmentary vertebrae, but due to the poor state of preservation, they cannot be assigned to any taxon. The places of deposition of these specimens are not known today.

As far as palaeoecology concerns, we cannot determine why Ophiotitanos was so abundant in Štramberk (especially in the Hradiště Formation) and what type of food it preferred. The occurrence of Squamophis? in the Kopřivnice and Hradiště Formations points to at least partly similar living conditions in a wider area, their survival for a prolonged time interval (Late Valanginian, Hauterivian, Barremian) or the re-establishment of the necessary living conditions. These euryalids are able to attach to objects rising above the bottom, spread their arms into the water current and feed on zooplankton.

Fauna from the Obecní Quarry, locality 2, is very different from the ophiuroid assemblages of the Aptian of Cuchía (Spain) and Wizard Way (Texas) (Thuy et al. 2014) but is very similar to the fauna from the Barremian of Serre de Bleyton (France; Thuy – Kroh 2011). Fauna from Blake Nose (Aptian and Albian, Atlantic Ocean off Florida; Thuy et al. 2012, Thuy 2013) also bears some resemblance to the aforementioned ophiuroid assemblage. It is also remarkable that, much like the localities of the nearshore depositional environments of the Bohemian Cretaceous Basin (Upper Cenomanian and Lower Turonian) (e.g., Štorc 1997), the assemblage from the Hradiště Formation comprises euryalids, ophiomusaids and ophiacanthins, with Ophiotitanos being the most frequent taxon.

References

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