Response of the Silurian jawed polychaete fauna to environmental changes during the Mid-Ludfordian Glaciation in the Prague Basin (Czech Republic)

The Basal Chotec or jugleri Event, close above the Lower–Middle Devonian boundary, has been regarded as a minor but important eustatic transgressive event, which is characterized by significant environmental changes, faunal extinction, appearance of new forms, and maximum radiation, particularly among the goniatites. This study contributes to a more precise stratigraphic allocation of the event, and provides a reconstruction of paleoenvironmental settings in the type area of the event, the Prague Basin (Czech Republic). The beginning of a transgression is recorded already in the Třebotov Limestone (partitus Zone, Eifelian, early Middle Devonian). The basin-wide change in the sedimentation pattern (onset of peloidal and crinoidal grainstones (calciturbidites) of the Chotec Formation) corresponding to the uppermost partitus and costatus conodont zones, base of Nowakia (Dmitriella) sulcatasulcata dacryoconarid Zone, and Pinacitesjugleri goniatite Zone is interpreted here to be linked to a maximum flooding of the basin. A hypothesis of enhanced nutrient load during sedimentation of the Chotec Formation is suggested here as a triggering mechanism for intense micritization and peloid formation and prasinophyte blooms, which could be, along with a greater depositional depth, responsible for oxygen deficiency and consequent reduction of diversity and habitat tracking among benthic invertebrates.

This study adds new data to complete the taxonomic revision of arthrodire placoderms from the Early Devonian of the Prague Basin (Czech Republic). It focuses on re-describing arthrodire specimens from the Emsian strata published more than a hundred years ago and associating them with unpublished material. The observations contradict previous taxonomic determinations of the Emsian arthrodires, which distinguished four species of three genera. Only one new genus and species is recovered—Johannaspis bohemicus (Barrande, 1872). The previous taxonomic splitting of the material into various genera is explained as a factor of specific taphonomical preservation in different localities of the Prague Basin. Another factor enabling the artificial splitting was the present location of the material in different institutions around the world. Together with Antineosteus rufus Vaškaninová & Kraft, 2014 based on previously unpublished specimens, they are the only two placoderm species known from the Emsian of the Prague Basin. Both are assigned to the homostiid arthrodires—large suspension feeders. The abundance of the Emsian placoderm fauna is very low in the Prague Basin; only a few specimens are known from each locality. However, they occur in a number of localities of Emsian age in the Prague Basin and in different environments, from very shallow (A. rufus) to relatively deeper marine environments, with all the occurrences being in limestones. The palaeogeographical distribution of homostiid arthrodires in the late Early Devonian was limited to tropical and subtropical shallow marine environments mainly in the southern hemisphere. In the Middle Devonian, the homostiids are no longer recorded from the northern continental margin of Gondwana including the Prague Basin area. However, they appear in Laurussia, Siberia and eastern Gondwana. The disappearance of environments with abundant food resources favourable for these large suspension feeders in the Prague Basin area could be related to the narrowing of the Rheic Ocean and gradual emerging of dry land as an early manifestation of the proceeding Variscan orogeny. This specific local palaeogeographical development of the Prague Basin area is considered the main reason for the significant decrease in diversity and abundance of placoderm fauna, which is in contradiction to the general trend.Valéria Vaškaninová [va.vaska@gmail.com], Institute of Geology and Palaeontology, Faculty of Science, Charles University, Albertov 6, Prague, 128 43, Czech Republic.

Klapper, G. and Vodražkova, S. 2013. Ontogenetic and intraspecific variation in the late Emsian - Eifelian (Devonian) conodonts Polygnathus serotinus and P. bultyncki in the Prague Basin (Czech Republic) and Nevada (western U.S.). Acta Geologica Polonica, 63 (2), 153-174, Warszawa. Samples from populations of Polygnathus serotinus Telford 1975 and P. bultyncki Weddige 1977 from the Prague Basin and Nevada display normal variation for Devonian conodont species. A considerable number of previous authors, however, have proposed unnecessary synonyms of these two species, primarily because they have not recognized ontogenetic variation. In contrast, we interpret the variation as ontogenetic as well as intraspecific and present detailed synonymies as a result. A third species, P. praetrigonicus Bardashev 1992, which has been carried in open nomenclature for many years, is an important indicator of the basal costatus Zone in the Prague Basin, New York, and Nevada. We review the stratigraphic distribution of these three species and the conodont zonation across the Emsian-Eifelian (Lower-Middle Devonian) boundary. Polygnathus pseudocostatus sp. nov. (partitus-costatus zones, central Nevada) is described herein. We have observed a decrease in the pit size during ontogeny in P. bultyncki although we have not measured enough specimens to rule out intraspecific versus ontogenetic variation.

Regional overprint of the GOBE: Dendroid graptolites reveal palaeoecological bias

Latest Ordovician jawed polychaetes, chitinozoans and depositional environments of the Levín section, Prague Basin, Czech Republic

The occurrence of placoderms in the Prague Basin (Bohemian Massif; Czech Republic) shows a very unsteady distribution in space and time. The most abundant specimens are in the Lochkovian and, through decrease in the Pragian, they become rare towards the Givetian. The primitive acanthothoracids dominating in the Lochkovian and Pragian are completely replaced by arthrodires at the beginning of the Emsian. All placoderms in the Prague Basin, without any regard to their dimensions, had smooth jaws which is a proof of their non-predatory feeding habit. Although placoderm diversity is generally considered to reflect the Devonian nekton revolution, the abundance of these vertebrates in the Prague Basin displays a decrease, i.e. an inverse tendency to the global one.

δ13C records across the late Silurian Lau event: New data from middle palaeo-latitudes of northern peri-Gondwana (Prague Basin, Czech Republic)

Palaeo-, rock magnetic and geochemical studies were conducted on volcanic samples from the Listice area to improve the knowledge of Palaeozoic volcanic evolution in the Prague Basin. The magnetic data display no significant differences between two studied localities, indicating one magnetizing event for both localities. Geochemical data suggest that Listice basalt could have originated from deep melting of the garnet peridotite mantle source during the attenuation and rifting of the continental lithosphere connected with asthenospheric mantle upwelling. The dataset furthermore supports the evidence of syn- or post- intrusive fluid interactions and low-temperature stages of alteration. The Ti-magnetite within amygdales of the samples was found to be carrying the characteristic remanent magnetization and reflects probably the Permo-Carboniferous remagnetization of volcanic phases.

Three trepostome bryozoan species are described from the Upper Ordovician Zahořany Formation of Loděnice, Prague Basin, Czech Republic. One genus is new—Lodenicella gen. nov. One species is described in open nomenclature. The described fauna contains ramose colonies or ramose branched projections from encrusting tubular-shaped colonies which inhabited shallow environment with moderate wave energy and significant influx of clastic material.

Late Ludlovian Chitinozoa from the locality “Na Požárech” (Silurian, Prague Basin, Barrandian area, Czech Republic)

Microboring organisms — an overlooked Early-Mid Palaeozoic marine ecosystem: Case study from the Prague Basin (Czech Republic)

Invertebrate epibionts on Ordovician conulariids from the Prague Basin (Czech Republic, Bohemia)

Abstract: Nautiloids of the superfamily Rutoceratoidea from the late Emsian (late Early Devonian) of the Prague Basin (Czech Republic) are commented upon. Species recognized include the hercoceratidsHercoceras mirum,H.?transiens,Ptenoceras proximum,P. nudum,P. minusculumandAnomaloceras anomalum, as well as the rutoceratidsAdelphoceras bohemicum,Homoadelphoceras devonicans,Pseudorutoceras bolliandGoldringia?devonicans. In addition, four new species are described:Parauloceras regularesp. nov.,Roussanoffoceras chlupacisp. nov.,Otomarocerassp. nov. andGoldringiasp. nov. Morphology and distribution patterns of Pragian and late Emsian rutoceratoid faunas from the Prague Basin are compared. They show that an increased diversity was accompanied by a higher level of specialization of rutoceratoids, which manifested itself in low abundance, increased facies dependence and greater variation in shell size during the Early Devonian. The evolution of sculpture and a contracted aperture, both regarded as protective adaptive features, was also examined, but no adaptive trend towards more pronounced sculpture and constriction of the aperture was found to have occurred in the Early Devonian. A more distinctive sculpture was, however, observed in shallow‐water assemblages ofP. proximumin comparison with deeper‐water faunules, and two additional cephalopod species were examined in order to obtain comparative data. The presence of distinct sculpture patterns in coeval shallow‐ and deeper‐water assemblages suggests limited migration between them and consequently reflects some degree of territoriality in Devonian nautiloids. New data on early shell development inP. proximumare presented. During the Choteč Event, rutoceratoid generic diversity dropped dramatically, one family became extinct and the Early Devonian diversification of the group came to an end. The recovery of nautiloid faunas was slower than that of other cephalopods and associated, unrelated invertebrates. The absence of change in abundance patterns between Pragian and late Emsian rutoceratoid faunas, i.e. prior to and subsequent to ammonoid radiation, suggests that the appearance and radiation of the latter group in the early Emsian did not affect the structure of nautiloid assemblages, i.e. these two clades did not occupy the same niches.

The Kozlowskii Event extinction in the Prague Basin is not prominent in number of extinct taxa among Ludfordian extinctions, but by its short duration and changes in community structure in both nektonic, pelagic and benthic faunas of different depth zones. The number of taxa going extinct is relatively low because some sensitive benthic and nectobenthic organisms (e.g., trilobites, cephalopods, gastropods, brachiopods) disappeared already at the base of the Neocucullograptus kozlowskii Zone contemporaneous with the beginning of a sea level highstand. The Kozlowskii Event includes two phases of extinction coinciding with two erosional sequence boundaries. The event also coincides with climatic changes and alterations of the ocean current regime. Sedimentary facies indicate that the first phase of extinction in the upper N. kozlowskii Zone took place during a sea level highstand situation. A lowstand with associated reduction in current activity occurred during the second phase of extinction in the lowermost Pseudomonoclimacis latilobus Zone. Recovery was completed in the upper P. latilobus Zone. The Kozlowskii Event is in the Prague Basin is accompanied by an abrupt change of benthic and pelagic communities and by immigrations from Baltica, Avalonia and Laurentia. The initial δ13C excursion correlates in the Prague Basin with the uppermost N. kozlowskii Zone after the last appearance datum of the conodont Polygnathoides siluricus.

This paper deals with a diverse fauna of polychaetes possessing jaws (= scolecodonts) from the late Silurian Kopanina Formation of the Prague Basin (Czech Republic). The most common genera are Kettnerites, Oenonites and Pistoprion; the entire collection contains at least 16 genera. This is in stark contrast to the four genera recorded from this region by previous authors. The fauna described shows great similarities with coeval ones reported from the Baltic area (Gotland and Estonia), Siberia, Arctic Canada and the British Isles. These new data thus extend the palaeobiogeographical and palaeolatitudinal distribution of several taxa, particularly at the genus but also the species level. The sampled interval embraces the Kozlowskii event and its effects on the polychaetes are briefly discussed. Although the collections are relatively small, particularly from post-event strata, a faunal reorganisation is apparent. The studied collection enabled the stratigraphical ranges of some taxa, including tretoprionids and possibly polychaeturids, to be extended into the late Ludlow. One new species, Mochtyella pragensis, is described. (Less)