Abstract
Echinoderms have long been considered to be one of the animal phyla that is strictly marine. However, there is growing evidence that some recent species may live in either brackish or hypersaline environments. Surprisingly, discoveries of fossil echinoderms in non-(open)marine paleoenvironments are lacking. In Wojkowice Quarry (Southern Poland), sediments of lowermost part of the Middle Triassic are exposed. In limestone layer with cellular structures and pseudomorphs after gypsum, two dense accumulations of articulated ophiuroids (Aspiduriella similis (Eck)) were documented. The sediments with ophiuroids were formed in environment of increased salinity waters as suggested by paleontological, sedimentological, petrographical and geochemical data. Discovery of Triassic hypersaline ophiuroids invalidates the paleontological assumption that fossil echinoderms are indicators of fully marine conditions. Thus caution needs to be taken when using fossil echinoderms in paleoenvironmental reconstructions.
Highlights
Numerous studies dealing with salinity level and its impact on modern echinoderms showed that this parameter is important in terms of their spatial distribution and size [1,2,3,4,5,6,7,8]
Modern echinoderms have a more limited salinity range than any other invertebrates because they have a permeable body wall and lack differentiated osmoregulatory or excretory organs [2,3,4,5,6,7,8,9]. This limit can especially be drawn for fossil echinoderms, among which only stenohaline taxa have been documented
An ophiuroid Ophiophragmus filograneus (Lyman) constitutes an echinoderm species living in the lowest salinity in the field [13]
Summary
Numerous studies dealing with salinity level and its impact on modern echinoderms showed that this parameter is important in terms of their spatial distribution and size [1,2,3,4,5,6,7,8]. Modern echinoderms have a more limited salinity range than any other invertebrates because they have a permeable body wall and lack differentiated osmoregulatory or excretory organs [2,3,4,5,6,7,8,9]. This limit can especially be drawn for fossil echinoderms, among which only stenohaline taxa have been documented. An ophiuroid Ophiophragmus filograneus (Lyman) constitutes an echinoderm species living in the lowest salinity in the field [13]. It has been pointed out that low salinity may lead to size abnormalities (dwarfism) [17,18,19,20]
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