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New echinoderm Lagerstätte from the Letná Formation (Sandbian, Upper Ordovician) of Bohemia
... Craniid brachiopods, bryozoans, edrioasteroid echinoderms, monoplacophorans and sphenothallids are often found attached to conulariid shells or, rarely, to exoskeletons of the odontopleurid trilobite Selenopeltis (Prokop 1965;Bruthansová and Van Iten 2020). The sandstones of the Letná Formation have yielded some exceptionally preserved weakly sclerotized, mainly euarthropod fossils, such as Furca, Duslia, aglaspidids and thylacocephalans, and other bivalved forms (Chlupáč1999a; Rak et al. 2009Rak et al. , 2013Van Roy et al. 2021); trilobites with preserved guts and frontal auxiliary impressions (Fatka et al. 2013;Fatka and Budil 2021); and unusual echinoderm assemblages (Nohejlová et al. 2019). This Konservat-Lagerstätte shows strong affinities to some of the Upper Ordovician Moroccan siliciclastic sequences of the Tafilalt Biota (Nohejlová et al. 2019;Van Roy et al. 2021;Budil and Fatka 2022). ...
... The sandstones of the Letná Formation have yielded some exceptionally preserved weakly sclerotized, mainly euarthropod fossils, such as Furca, Duslia, aglaspidids and thylacocephalans, and other bivalved forms (Chlupáč1999a; Rak et al. 2009Rak et al. , 2013Van Roy et al. 2021); trilobites with preserved guts and frontal auxiliary impressions (Fatka et al. 2013;Fatka and Budil 2021); and unusual echinoderm assemblages (Nohejlová et al. 2019). This Konservat-Lagerstätte shows strong affinities to some of the Upper Ordovician Moroccan siliciclastic sequences of the Tafilalt Biota (Nohejlová et al. 2019;Van Roy et al. 2021;Budil and Fatka 2022). The fine-grained distal sediments of the Letná Formation contain rare linguliform brachiopods, an atheloptic trilobite association and cyclopygid trilobites (Fatka and Mergl 2009;Fatka et al. 2013). ...
The lower Palaeozoic succession of central Europe exposed in the Bohemian Massif is a classic area of geology with a long-standing tradition of research dating back to the 18th century. The Ordovician rocks form parts of sections in several units that sit on the Cadomian basement. These sedimentary and volcano-sedimentary fillings of partial depressions in the basement are relics of the system of rift basins in the Gondwanan margin reflecting the rifting of the Rheic Ocean. The Ordovician sections are related to the subsidence period during the extensional regime accompanied by volcanism. They are underlain by Neoproterozoic or Cambrian rocks and continue up usually without breaks. After closure of the Rheic Ocean due to the Gondwana-Laurussia collision, the Ordovician successions were incorporated into the Variscan Orogen belt and preserved in denudation relics such as the Bohemian Massif and its units. Ordovician strata with Gondwanan shelf affinities can be traced along the Variscans from Spain to central Europe, and are reflected in the regional stratigraphic scale based mainly on the succession in the Prague Basin. The Ordovician fill of this accumulation centre, together with relics of another preserved in the Schwarzburg Anticline, represent the main exposures in the Bohemian Massif. The individual features of the Ordovician successions, such as facies developments, fossil associations, and volcanism, make them model areas both for understanding the palaeogeographic and geotectonic evolution of the peri-Gondwanan margin and as cool-water stratigraphic standards.
... In the Upper Ordovician of Bohemia and the Central Iberian Zone, Dendrocystites occurs in shallow environmental conditions and is associated with echinoderm faunal elements both very similar to those documented in the western Tafilalt area. For example, the recently discovered Chrustenice echinoderm Lagerstätte (Sandbian, Letná Formation) yielded slabs covered by abundant, densely packed, current-oriented, fully articulated specimens of Dendrocystites (Fig. 7), associated with crinoids, edrioasteroids, ophiuroids, glyptocystitid rhombiferans (Homocystites) and stylophorans (Nohejlová et al. 2019). Similarly, Dendrocystites was collected at Viso del Marquès (southern Central Iberian Zone) in shallow, storm-generated, fine black shales with intraformational pebbles of the Cantera Shale, associated with crinoids, glyptocystitid rhombiferans (Homocystites) and stylophorans (Gil Cid et al. 1996;Lefebvre et al. in press). ...
... sedgwicki. In the Upper Ordovician of the Prague Basin, several new, yet undescribed examples of edrioasteroids attached to the thecal surface of Dendrocystites could support the brachiole downward orientation model(Nohejlová et al. 2019). ...
... In the Upper Ordovician of Bohemia and the Central Iberian Zone, Dendrocystites occurs in shallow environmental conditions and is associated with echinoderm faunal elements both very similar to those documented in the western Tafilalt area. For example, the recently discovered Chrustenice echinoderm Lagerstätte (Sandbian, Letná Formation) yielded slabs covered by abundant, densely packed, current-oriented, fully articulated specimens of Dendrocystites (Fig. 7), associated with crinoids, edrioasteroids, ophiuroids, glyptocystitid rhombiferans (Homocystites) and stylophorans (Nohejlová et al. 2019). Similarly, Dendrocystites was collected at Viso del Marquès (southern Central Iberian Zone) in shallow, storm-generated, fine black shales with intraformational pebbles of the Cantera Shale, associated with crinoids, glyptocystitid rhombiferans (Homocystites) and stylophorans (Gil Cid et al. 1996;Lefebvre et al. in press). ...
... sedgwicki. In the Upper Ordovician of the Prague Basin, several new, yet undescribed examples of edrioasteroids attached to the thecal surface of Dendrocystites could support the brachiole downward orientation model(Nohejlová et al. 2019). ...
In the western Tafilalt area, eastern Anti-Atlas (Morocco), solutan echinoderms are a major faunal element of most echinoderm Lagerstätten occurring within the Lower Ktaoua Formation (late Sandbian-early Katian). For the first time, members of the class Soluta are formally described from Morocco and Africa. All solutans from the Lower Ktaoua Formation are identified as Dendrocystites aff. sedgwicki . Three size-related morphotypes, probably corresponding to successive growth stages (‘juvenile’, ‘adult’ and ‘gerontic’), could be distinguished within the abundant and well-preserved material from Morocco. The occurrence of the genus Dendrocystites in the western Tafilalt confirms the strong faunal affinities between Morocco and other regions of the Mediterranean Province (Czech Republic and Spain) in Late Ordovician times. In high palaeolatitude (peri-)Gondwanan areas, Dendrocystites was a gregarious solutan living in shallow, siliciclastic settings at or above storm-wave base.
In the Lower Ordovician of Morocco, solutan echinoderms are relatively common, locally abundant, geographically widespread (Central and Eastern Anti-Atlas), and biostratigraphically long-ranging (late Tremadocian–mid Floian) components of the Fezouata Biota. The lower part of the Fezouata Shale (late Tremadocian) yielded one specimen, here tentatively identified as a Castericystis-like syringocrinid, with exceptionally preserved internal soft parts presumably corresponding to the distal region of the gut. Most solutan remains from the Fezouata Shale are assigned to Plasiacystis mobilis, which was already known from the late Tremadocian of France and the Darriwilian of the Czech Republic and United Kingdom. Several isolated dististeles provisionally identified as Plasiacystis sp. may belong to large individuals of P. mobilis or a new taxon. Several specimens of late Tremadocian solutans from the Fezouata Shale, morphologically intermediate between Minervaecystis vidali (late Tremadocian, France) and Plasiacystis mobilis, are assigned to Nimchacystis agterbosi gen. et sp. nov. The diagnosis of the syringocrinid family Minervaecystidae is modified to include the four genera Minervaecystis, Nimchacystis, Pahvanticystis, and Plasiacystis, all characterised by an ovoid theca, a laterally inserted feeding appendage, and a twisted, flattened dististele. Minervaecystids are interpreted as active epibenthic detritus feeders, using their dististele to crawl on soft substrates. The newly described solutan taxa highlight that the benthic communities of Fezouata Biota are more diverse than what was previously described.
Cornute stylophorans are a minor, though typical component of Middle-Late Ordovician echinoderm assemblages adapted to soft siliciclastic substrates, in high latitude peri-Gondwanan regions. All previously reported occurrences of Darriwilian-Katian cornutes from Czech Republic, France, Morocco and Spain are revised and their plate homologies reassessed. The genera Beryllia and Juliaecarpus are reinterpreted as junior synonyms of Domfrontia , and Thoralicystis is synonymised with Bohemiaecystis . Several Mediterranean scotiaecystids previously assigned to Bohemiaecystis and/or Scotiaecystis are placed within Thoralicarpus gen. nov., and cornute taxa originally left in open nomenclature by Chauvel are formally described as Bohemiaecystis chouberti sp. nov. (AVI) and Destombesicarpus izegguirenensis gen. et sp. nov. (AVIII). Other new Mediterranean taxa include Arauricystis clariondi sp. nov., Destombesicarpus budili gen. et sp. nov., Milonicystis reboulorum sp. nov., Thoralicarpus bounemrouensis gen. et sp. nov., and T . prokopi gen. et sp. nov. The six cornute genera identified in Darriwilian-Katian Moroccan echinoderm Lagerstätten are also present in coeval assemblages of at least one other Mediterranean region, thus supporting the existence of strong faunal affinities between the Anti-Atlas, the Armorican Massif, the Barrandian area and the Iberian Peninsula.
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