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Bulletin of Geosciences

Ghavidel-Syooki M, Popov LE, Álvaro JJ, Ghobadi Pour M, Tolmacheva TY, Ehsani M-H; Vol. 89, issue 4, pages 679 - 706The Lower-Middle Ordovician sediments exposed in the Faraghan Mountains, south-eastern Zagros Ranges, represent a condensed succession of siliciclastic-dominated rocks rich in palynomorph assemblages (acritarchs and subsidiary chitinozoans) and sparse shelly concentrations bearing biostratigraphically significant brachiopods and conodonts. The Lower Ordovician Zard-Kuh Formation comprises coarse-grained siliciclastic deposits rich in Cruziana ichnofossils. The lower 80 m of the overlying Seyahou Formation, late Floian to Katian in age, form a heterolithic succession composed of black and green shales, subarkoses and silty limestones. Its lower part is punctuated by a centimetric phosphoarenite that contains lingulate brachiopods (Atansoria yaseri sp. nov.) and conodonts (Baltoniodus aff. B. triangularis Lindström and Drepanoistodus sp.) that suggest a latest Floian age. The top of the condensed phosphoarenite is marked by a considerable hiatus that ranges the Dapingian and early Darriwilian interval. Overlying the hiatus, the Seyahou Formation comprises two fossiliferous levels, the oldest dated as mid-Darriwilian with chitinozoans characteristic of the Siphonochitina formosa Zone, and the youngest of the Katian Acanthochitina barbata Zone. Mid Ordovician phosphogenesis associated with starvation, reworking, resedimentation, and the onset of distinct stratigraphic gaps was a complex process recorded throughout the Arabian margin of Gondwana. In the Zagros Ranges, maximum flooding and phosphate precipitation are suggested as the counterpart of the Helskjer Drowning Event of Baltoscandia and the third-order maximum flooding surface that punctuates the Siphonochitina formosa Zone in North Africa.

http://www.geology.cz/bulletin/contents/art1453 2014/10/02 - 20:58

Hyžný M, Hoch I, Schram FR, Rybár S; Vol. 89, issue 4, pages 707 - 717A newly found specimen of an aeschronectid hoplocaridan Crangopsis cf. socialis (Salter, 1861) from the Lower Carboniferous (Mississippian) of the Ostrava Formation (Czech Republic) represents the first occurrence of Aeschronectida from continental Europe. The studied specimen preserves all thoracopods allowing careful description. Morphological similarities between the present material and its relative Kallidecthes richardsoni Schram, 1969 allows reassignment of Crangopsis from Aratidecthidae to Kallidecthidae, leaving the former family with only its type genus Aratidecthes. Thoracopod morphology of Crangopsis socialis based on the present material suggests an upraised posture of the animal during its life. The upraised posture might have developed independently at least twice within Hoplocarida, in Aeschronectida and Stomatopoda. The body of Crangopsis socialis, and consequently of all aeschronectids, is divided into four tagmata: the sensorial unit, the food-processing unit, the walking-appendage area, and the pleon plus tailfan in contrast to five in Stomatopoda.

http://www.geology.cz/bulletin/contents/art1458 2014/10/02 - 20:58

Duarte LV, Comas-Rengifo MJ, Silva RL, Paredes R, Goy A; Vol. 89, issue 4, pages 719 - 736Here, we present an integrated stratigraphical study across the Sinemurian-Pliensbachian interval cropping out into the Portuguese reference section of S. Pedro de Moel (Lusitanian Basin). Characterized by marl-limestone alternations of the Água de Madeiros Formation (subdivided into Polvoeira and Praia da Pedra Lisa members), this succession is particularly dominated by organic-rich facies (black shales) and contains a diverse fauna of benthic and nektonic macrofossils. This stratigraphic and sedimentary setting is the basis for a high-resolution carbon isotope study, constrained by new ammonite biochronostratigraphic determinations and other palaeontological data. The new ammonite collections characterize the Oxynotum and Raricostatum chronozones and the Raricostatum, Macdonnelli and Aplanatum subchronozones, and accurately identify the Sinemurian-Pliensbachian boundary in this western Iberian margin setting. Carbon isotope measurements were made from bulk carbonate (δ13Ccarb) from 351 samples, representing the Oxynotum to earliest Jamesoni (early Taylori) Chronozone intervals. The carbon isotope values exhibited a large range, varying between +2.85‰ in the Oxynotum Subchronozone to very negative values observed in some limestone beds from the Raricostatum Subchronozone (lowest reaching -6.7‰), a variation clearly controlled by lithological and facies changes. Despite these strong anomalous isotopically light values (below -2‰), which are clearly associated with organic matter degradation and early diagenesis, the δ13Ccarb curve shows a long-term negative trend across the Oxynotum to the early Taylori Subchronozone interval. This tendency is reversed around 5 m above the Sinemurian-Pliensbachian boundary, and the δ13Ccarb values become positive correlative with an absence of organic matter and argillaceous sediments in the limestone beds of Praia da Pedra Lisa Member. Although the δ13C data recorded across the Sinemurian-Pliensbachian of the Lusitanian Basin had been controlled by internal depositional conditions, the general evolution of carbon isotopes agrees with the trend recognized in other basins.

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Denayer J; Vol. 89, issue 4, pages 737 - 771In Northwestern Turkey, the Mississippian (Lower Carboniferous) Yılanlı Formation is composed of variegated shallow- water limestone containing rugose corals, tabulate corals and brachiopods. Six sections were sampled in the Zonguldak and Bartın areas, from east to west, there are Süzek, Topluca, Gökgöl, Kokaksu, Ulutam and Kisla sections. Among the rugose corals, a rich and diversified assemblage of Lithostrotionidae has been collected. The latter contains the species: Nemistium cf. affine, Siphonodendron ondulosum, S. martini, S. irregulare, S. pauciradiale, S. asiaticum, S. rallii sp. nov., S. scaleberense, S. kleffense, S. aff. kleffense, Lithostrotion araneum, L. vorticale, L. sp. and L. potii sp. nov. During the Moliniacian it is proposed that subcerioid colonies of S. ondulosum gave rise to cerioid colonies of Lithostrotion potii sp. nov., the latter constituting the oldest species of the genus previously considered to be Livian to Warnantian in age. This discovery led to an emendation of the phyletic lineage of the Lithostrotionidae. The biostratigraphy based on rugose corals indicates a Moliniacian (early Viséan) and Warnantian (late Viséan) age of the deposits with the absence of the intervening Livian (middle Viséan).

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Opluštil S, Pšenička J, Bek J, Wang J, Feng Z, Libertin M, Šimůnek Z, Bureš J, Drábková J; Vol. 89, issue 4, pages 773 - 818A Middle Pennsylvanian tuff bed (the Bělka bed) in the roof of the Lower Radnice Coal bears T0 t-forming vegetation preserved in growth position. This vegetation has been studied in detail at the 12 hectares large Ovčin coal deposit in the southern part of the Radnice Basin. Documentation of the fossil record in six excavations and that previously collected in the former opencast mine allowed for a detailed reconstruction of the local peat-forming lepidodendrid-cordaitalean forest structured into well-developed stories. It consists of about 33 species, which colonized the occasionally flooded planar peat swamp precursor of the Lower Radnice Coal. The canopy story of this vegetation was dominated by Lepidodendron (Paralycopodites) simile, L. lycopodioides, Lepidophloios acerosus and Cordaites borassifolius. They formed a relatively dense canopy, locally interrupted with significant gaps allowing development of a rich groundcover that together with liana-like plants represents the most diverse part of the forest. A less diverse understory composed of calamites, medullosan pteridosperms and Psaronius tree ferns displays a patchy distribution pattern presumably related to density of the canopy. The minimal area that sufficiently represents the pattern of this forest phytocoenosis is estimated to be about 200 m2, although lower stories are well represented even within much smaller areas of about 60 m2. Slight heterogeneity in the population density of dominant taxa (Cordaites vs. lepidodendrid lycopsids) was documented across the Ovčin coal deposit. The fossil record of the Bělka tuff bed also indicates that the coal-forest colonizing the peat swamp prior the generation of forest killed by volcanic ash fall, was destroyed, presumably due to long-lasting flooding and thus suggests that catastrophic events were probably a relatively common part of the evolution of peat-forming Pennsylvanian successions.

http://www.geology.cz/bulletin/contents/art1499 2014/10/02 - 20:58

Harzhauser M, Neubauer TA, Georgopoulou E, Harl J; Vol. 89, issue 4, pages 819 - 908We present a critical evaluation of the Early Miocene terrestrial and aquatic mollusc fauna of the North Bohemian Lake in the Most Basin in the Czech Republic. In total, 90 species (8 aquatic and 81 terrestrial gastropods, one bivalve) are documented from that lake system that had formed within the North Bohemian Rift. Only three of these species are newly recorded for the Most Basin, suggesting that the fauna is well sampled. Based on historical collections of the Natural History Museum in Vienna, which were partly acquired by quantitative bulk samples from Tuchořice, a rough estimate of the composition of the terrestrial assemblage can be presented. More than 80% of the >30,400 shells are represented by carychiids, vertiginids and valloniids, suggesting the presence of densely forested wetlands fringing the North Bohemian Lake. About 57% of the terrestrial species are known so far exclusively from the Most Basin. This high degree of “endemism”, however, is rather a result of the still very fragmentary knowledge of coeval European faunas. Discus rasseri Harzhauser, Neubauer & Georgopoulou sp. nov. and Discus zagorseki Harzhauser, Neubauer & Georgopoulou sp. nov. are described as new species and Esuinella Harzhauser, Neubauer & Georgopoulou gen. nov. (Valloniidae), Nordsieckula Harl & Harzhauser gen. nov. (Orculidae), and Manganellia Harzhauser, Neubauer & Georgopoulou gen. nov. (Discidae) are introduced as new genera. Serrulastra (Serruplica) tuchoricensis nom. nov. is proposed as replacement name for Clausilia laevigata Frankenberger, 1914.

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Noailles F, Lefebvre B, Kašička L; Vol. 89, issue 3, pages 451 - 476The morphology of the Late Ordovician solutan Dendrocystites is reevaluated based on more than 300 specimens from the Letná and Zahořany formations (Prague Basin, Czech Republic). This genus is reported for the first time from the Bohdalec Formation, and its presence is confirmed in the Vinice Formation. The morphology of all specimens of the stratigraphically older species D. barrandei (Sandbian) is identical to that of small to medium-size individuals of D. sedgwicki (Katian). Distinctive characters of D. sedgwicki occur only in the largest specimens, and are all size-related (more asymmetrical thecal outlines, stronger ornamentation, rosetting pattern of thecal plates, proliferation of platelets in the proxistele). Consequently, the transition from D. barrandei to D. sedgwicki is interpreted as the result of heterochronic processes, with the largest individuals of D. sedgwicki displaying hyperadult morphologies (hypermorphosis). Dendrocystites is locally abundant in both the Letná and Zahořany formations, but extremely rare in the deeper deposits of the Vinice and Bohdalec formations. This pattern coincides closely with first order fluctuations of the sea-level in the Prague Basin. The life orientation and implied feeding strategy of Dendrocystites and other solutans are both critically discussed. Several independent lines of evidence suggest that solutans were more likely detritus-feeders. Finally, it is proposed that two morphologically distinct patterns of dististele organization were elaborated independently from the polyplated, undifferentiated stalk-like appendage of Coleicarpus (plesiomorphic condition). Consequently, amajor subdivision of the class Soluta into two main clades (Dendrocystitida ord. nov. and Syringocrinida ord. nov.) is proposed. The monophyly of each order is supported by apomorphies based primarily on the organization of the dististele and the morphology of the periproct. “Dendrocystites” rossicus is reinterpreted as belonging to an unknown genus of syringocrinids, whereas Heckericystis kuckersiana may represent a third species of Dendrocystites.

http://www.geology.cz/bulletin/contents/art1475 2014/06/12 - 16:03

Maletz J ; Vol. 89, issue 3, pages 477 - 540This paper presents a proposal for a taxonomic approach to the classification of the Pterobranchia (Cephalodiscida and Graptolithina) to be adopted for the revision of the Treatise on Invertebrate Paleontology, Part V (Hemichordata), currently in preparation. A combination of traditional Linnaean taxonomy, supported by cladistic analyses in some groups is proposed herein as a practical solution for the classification of the Graptolithina as for many groups a cladistic analysis has never been attempted and is unlikely to be undertaken in the near future. The number of ranked taxa has been kept as low as possible, with all genus level taxa referred to a family. All families and higher taxonomic units are discussed, but new taxa have not been introduced. Paraphyletic (but not polyphyletic) taxa are accepted as useful units in this classification. A number of recently introduced taxonomic units, based on cladistic analyses (e.g. Eugraptoloida, Pan-Reclinata, Pan-Bireclinata), are discussed in the context of this classification and the usefulness of these taxa is critically evaluated. The solution proposed here opts not to name a number of nodes from the published cladistic analyses that potentially could be named and in some cases have been named - not to inflate the hierarchy of the used taxonomic system. Taxa are kept as close as possible to their original definition and not unnecessarily expanded or restricted. The taxonomy proposed here for the Graptolithina indicates that the extensive use of higher level taxa, e.g. orders for small groups of genera as has been done for many benthic graptolite groups in the past is unnecessary and should be avoided.

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Haug JT, H&uuml, bers M, Haug C, Maas A, Waloszek D, Schneider JW, Kerp H; Vol. 89, issue 3, pages 541 - 552Arthropod cuticles from the Mississippian (Early Carboniferous, Viséan) Hainichen Subgroup, Erzgebirge Basin, have been encountered in bulk-macerated samples from a roadcut exposure in Chemnitz-Glösa, eastern Germany. The cuticles are described in detail and compared with larger faunal components known from the same horizons. Part of the specimens represent remains of arthropod appendages, while others, though exhibiting fine detail of surface texture, could not be assigned to certain body regions. In all cases it remains difficult to assign the fragments from Chemnitz-Glösa to taxa known from the Hainichen Subgroup or from other localities yielding arthropod remains of similar preservation. However, it is suggested that several specimens may represent scorpion remains, either limb parts (piece of the pedipalp, distal claw of walking limb) or fragments of the body surface. One specimen, a single appendage element, could represent the first insect fragment from this locality. All fragments appear to be terrestrial faunal components. Chemnitz-Glösa is one of the very few Lower Carboniferous localities to yield remains of terrestrial arthropods and the only one outside Scotland.

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Ortega-Blanco J, McKellar RC, Engel MS; Vol. 89, issue 3, pages 553 - 571Platygastroid wasp diversity in Álava amber is reviewed. Platygastroids are the most numerous group of Hymenoptera in Spanish amber, a pattern typical for many Cretaceous amber deposits, with species of the superfamily sometimes more abundant than all other arthropod lineages. Herein we report on 87 specimens, 62 of them sufficiently preserved to permit specific identification, and all dating from the Lower Cretaceous (middle Albian). Eight new genera and nine new species are described and figured as Proterosceliopsis gen. nov., Proterosceliopsis masneri sp. nov., Bruescelio gen. nov., Bruescelio platycephalus sp. nov., Tithonoscelio gen. nov., Tithonoscelio resinalis sp. nov., Amissascelio gen. nov., Amissascelio temporarius sp. nov., Juxtascelio gen. nov., Juxtascelio interitus sp. nov., Alavascelio gen. nov., Alavascelio delvallei sp. nov., Electroteleiopsis gen. nov., Electroteleiopsis hebdomas sp. nov., Perimoscelio gen. nov., Perimoscelio tyrbastes sp. nov., and P. confector sp. nov. Morphological interspecific variability is low, hindering identification, and as such, taxa are principally diagnosed on structure of the female antenna, tibial spur formula, mesoscutal form, and head and metasomal anatomy. The taxa are discussed in relation to other fossil lineages of platygastroids as well as modern counterparts. All species belong to the “Scelionidae”, a paraphyletic group relative to Platygastridae as currently circumscribed (including Platygastrinae, Scelioninae, Teleasinae, Telenominae). Platygastroid diversity will certainly rise in Spanish amber as abundant new material becomes available from the El Soplao and San Just outcrops. The name Jordanoscelio nom. nov. is proposed to replace the homonymous Microptera Kaddumi for a Jordanian amber (Early Cretaceous) genus of Scelionidae, resulting in Jordanoscelio attiki (Kaddumi) comb. nov.

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López-Guerrero P, Álvarez-Sierra MA, García-Paredes I, Peláez-Campomanes P; Vol. 89, issue 3, pages 573 - 592A new species of Cricetodontini (Cricetidae, Rodentia, Mammalia), Cricetodon nievei sp. nov. from the Toril section (Toril 3A, Toril 3B, Toril 2) and Las Planas 5H is described. All this sites belong to the local biozone G3 (late Aragonian, late middle Miocene) from the Calatayud-Daroca Basin (Zaragoza, Spain). The new species displays a mosaic pattern consisting in a combination of primitive and derived characters: the upper molars have a basal Cricetodon-like pattern - short and not complete ectolophs -, whereas the lower molars share several derived features with the older representatives of Hispanomys - absence of metalophulid II. The generic assignation of the new taxon is further discussed and it is compared with all the species of Cricetodon and Hispanomys described until date. This mosaic evolutionary pattern of dental characters is also recognized in other species of Cricetodontini from Europe during the late Aragonian, although involving different combination of morphological characters. At this time, the diversity of the tribe increases, including species with complex morphology and higher intraspecific variability than the older representatives. The new species proposed here is morphologically close to Cricetodontini recorded outside the Calatayud-Daroca Basin, especially C. albanensis and H. decedens from France. Finally, the palaeoecological context of the new species is discussed; the stratigraphical distribution of Cricetodon nievei sp. nov. coevals changes in the faunal assemblages which are possibly related to an increase of humidity detected in the Calatayud-Daroca Basin.

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Niedźwiedzski G, Narkiewicz M, Szrek P; Vol. 89, issue 3, pages 593 - 606The dolomitic deposits of the Middle Devonian Wojciechowice Formation exposed at the tetrapod tracksite in the Zachełmie Quarry in the Holy Cross Mountains (Poland) are characterised by a low diversity of invertebrate trace fossil association. Four ichnoassemblages can be identified in the track-bearing, lower part of the succession. The most conspicuous are trace fossils produced by arthropods (probably crustaceans), which can form distinctive and large horizontal burrows. The described ichnotaxa (cf. Skolithos isp., cf. Balanoglossites isp., Alcyonidiopsis isp., Spongeliomorpha isp., Gordia isp., and Rhizocorallium isp.) are well known from typical marginal-marine and shallow-marine deposits. Nevertheless, the studied assemblages were found in sparsely distributed horizons and are dominated by a single or a few ichnotaxa with locally high trace-densities. Distribution and composition of the trace fossil assemblages probably reflects occurrence of the impoverished, stressed Cruziana ichnofacies. It was affected by changes in water depth with intermittent periods of subaerial exposure connected with salinity fluctuations. The invertebrate trace fossil assemblage, tetrapod tracks and associated sedimentological features point to deposition in a marginal-marine, mostly peritidal and lagoonal environment with minor terrestrial influences.

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Sartenaer P; Vol. 89, issue 3, pages 607 - 616Jacoburbirostrum gen. nov., type species Atrypa duplicata Hall, 1843, is described from the middle Famennian (II-G) of southwestern New York State, and a lectotype is formally designated. New family Jacoburbirostridae is established.

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Frýda J, Frýdová B; Vol. 89, issue 3, pages 617 - 634The Homerian (late Wenlock, Silurian) carbon isotope excursion is documented for the first time from peri-Gondwana based on new data from the Barrandian (Perunica). It is also the first time that this excursion has been found outside of the palaeoplates that subsequently formed the supercontinent Laurussia (i.e., Laurentia, Baltica and Avalonia). The typical two-peaked Homerian δ13C excursion is documented from a highly fossiliferous shallow-water limestone succession formally established here as the Kozel Limestone Member of the Motol Formation. Application of δ13C chemostratigraphy considerably improves the stratigraphic resolution within the Kozel Limestone Member and enables more precise dating of its very diverse fauna. The present data reveal recovery of benthic communities after a series of mid-Homerian extinction events (i.e., the Mulde conodont and the end lundgreni graptolite bioevents) started much earlier than has been hitherto described from other world occurrences.

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Vaškaninová V, Kraft P ; Vol. 89, issue 3, pages 635 - 644Antineosteus rufus sp. nov. from the upper Emsian of the Czech Republic is described based on two fragments of large dermal plates discovered in the Suchomasty Limestone. The original length of the animal is inferred to have exceeded that of Tityosteus rieversae - the largest Lower Devonian placoderm recorded so far. The occurrence of A. rufus in the Prague Basin is consistent with other giant homostiids in several areas. These animals were apparently adapted to plankton- feeding, although they appeared in the conditions of collapsed diversity of the planktic communities during the “Devonian Nekton Revolution”. This successful feeding strategy made them the first vertebrates occupying the nutrient-rich ecospace producing the largest animals up to the present.

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Baranov VV, Slavík L, Blodgett RB ; Vol. 89, issue 3, pages 645 - 678In late Pragian and early Emsian strata of the Izvestkovyi Karier - II section of Northeast Asia is found a continuous sequence of representatives of the family Polygnathidae which testify to the synthetic nature of the currently used conodont zonal scales. In this time interval are recognized three phylogenetic lineages of polygnathids: Polygnathus sobolevi Po. ivanowskyii, Polygnathus kitabicus →Po. bardashevi and Polygnathus settedabanicus →Po. nothoperbonus. Fifteen species of polygnathids including mostly newly described taxa are documented here: Polygnathus alkhovikovae sp. nov., Po. arthuri sp. nov., Po. bardashevi sp. nov., Po. dehiscens (Philip & Jackson, 1967) late morphotype, Po. excavatus (Carls & Gandl, 1969), Po. ivanowskyii sp. nov., Po. karsteni sp. nov., Po. kitabicus (Yolkin et al., 1994), Po. lezhoevi sp. nov., Po. michaelmurphyi sp. nov., Po. nothoperbonus (Mawson, 1987), Po. perbonus (Philip, 1966), Po. sobolevi Bardashev, Weddige & Ziegler, 2002, Po. settedabanicus sp. nov., and Po. yakutensis sp. nov. Early Emsian time in Northeast Asia is characterized by an intense speciation and radiation within its conodont fauna during a relatively short interval between the Polygnathus excavatus and Polygnathus nothoperbonus zones. The Pragian Stage (Middle Early Devonian) is characterized by a maximum transgression that led to increased migration of faunal associations of tabulate and rugose corals, brachiopods and conodonts in the marginal seas of Angarida. The position of the lower and upper boundaries of the Pragian Stage in this region is clarified and their correlations are shown with the adjoining Verkhoyansk-Chukotsk (Kolyma region), Taimyr, West Siberian, and Altai-Sayan marginal seas.

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Budil P, Fatka O, Holloway D, Hughes NC; Vol. 89, issue 2, pages 201 - 202

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Bruton DL; Vol. 89, issue 2, pages 203 - 206

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Shiino Y, Kuwazuru O, Suzuki Y, Ono S, Masuda C; Vol. 89, issue 2, pages 207 - 218The mode of life of the remopleuridid trilobite Hypodicranotus striatulus Walcott (1875) was examined hydrodynamically with a special focus on the relationship between the autecological performances of swimming and feeding. To understand the effect of swimming height from the sea bottom on the hydrodynamic performance of the exoskeleton, we performed computational fluid dynamics simulations on four models at differing distances from the sea bottom. The results indicated that Hypodicranotus could launch itself from the sea bottom with a relatively strong hydrodynamic lift force from slow walking or swimming speeds. However, the lift force decreased as the swimming height increased at slow swimming speeds. Hence, Hypodicranotus would have had to increase its swimming speed to greater than 0.2 m/s and to obtain the most stable lift force at a swimming height equal to half of its own body height. Its exoskeletal morphology, with a forked hypostome, enabled it to launch itself at a slow velocity and swim at a modest distance, i.e., close to its own height, from the sea bottom. Feeding from the median vortex flows along the food groove between the two prongs of the hypostome may have been the best strategy near the sea bottom, where a large amount of food matter would have been available. Because arthropod musculature consists of striated muscles, which exhibit inferior endurance, Hypodicranotus most likely adapted to the near-bottom environment, where it could rest at times on the sea bottom as part of a nektobenthic mode of life.

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Hughes NC, Kříž J, Macquaker JHS, Huff WD; Vol. 89, issue 2, pages 219 - 238Excavation of Joachim Barrande’s classic fossil locality of the “Aulacopleura shales” exposed on Na Černidlech Hill, near Loděnice reveals that most specimens were recovered from a 1.4 m interval exposed in “Barrande’s pits”. These are located at the eastern end of a 0.4 km trench dug in the mid 1800’s to expose the interval along strike. Over an hundred bedding planes occur within the 1.4 m interval, and thousands of articulated trilobites have been collected at the site. Individual bed surfaces vary in the density, size, and taxonomic composition of the fossils contained. Some preserve a diverse benthic shelly fauna, others are almost exclusively dominated by the trilobite Aulacopleura koninckii, and a third variety is apparently barren of all shelly fossils. Isolated sclerites of A. koninckii are rare, and on almost all bedding surfaces exoskeletons are predominantly partially articulated and lack both alignment and sclerite fragmentation. The occurrence of A. koninckii conforms in many ways to the characteristics of a Type I trilobite lagerstatte of Brett et al. (2012). The presence of enrolled A. koninckii suggests that final burial may have resulted from relatively rapid obrution, although the condition of partial articulation indicates that many carcasses or exuviae partially disaggregated before burial. The mean size and density of A. koninckii specimens varies markedly among bedding planes, with some assemblages entirely comprised of juveniles, suggesting that notably dense trilobite clustering was not restricted only to reproductively mature individuals. The presence of multiple clusters of different mean specimen size partly accounts from the unusually comprehensive record of the articulated meraspid and holaspid ontogeny of this species at this locality. Limited bioturbation suggests a dysoxic substrate, and the olenimorphic form and distribution of A. koninckii, combined with a lack of encrustation or predation upon it, suggests that this species may have periodically bloomed in abundance at particular oxygen concentrations that largely excluded other skeletonized benthos. Some bedding plane assemblages might represent mass mortality events, perhaps as available oxygen passed below levels necessary to maintain the metabolism of A. koninckii.

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Aceñolaza GF, Albani R, Bernárdez E, García-Bellido DC, Gutiérrez-Marco JC, Rábano I, Sá AA; Vol. 89, issue 2, pages 239 - 244The first Furongian trilobites are described herein from the Cambrian of the Cantabrian Zone,NWSpain. They were collected during the construction of the “Túnel Ordovícico del Fabar” from the shales of “El Fabar Beds” in the La Matosa member of the Barrios Formation. The assemblage includes the aphelaspidine genus Maladioidella, with a specimen identified as M. cf. colcheni, a species previously known from Sierra de la Demanda (Spain), and possibly Sardinia and Oman. Fragments of an indeterminate olenid trilobite and phyllocarid crustaceans have also been recorded. Based on the acritarch assemblage, these beds are considered as late Jiangshanian or earliest Stage 10 of the Cambrian System. The ichnofossil Cruziana semiplicata has also been collected in the tunnel from the upper part of the Ligüeria Member (Tremadocian) of the Barrios Formation, clearly postdating the occurrence of Maladioidella colcheni, its supposed tracemarker according to some authors. The separate record of both taxa (a Furongian trilobite and a Cambro-Ordovician trace fossil) does not support this statement, so their relationship would be refuted in this case.

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Hýžný M, Kočová Veselská M, Dvořák P; Vol. 89, issue 2, pages 245 - 256Because of close morphological affinities, fossil cheliped fragments of the ghost shrimp Ctenocheles (Decapoda, Axiidea, Ctenochelidae) can be easily misidentified as remains of different decapod crustacean taxa. Re-examination of the Cretaceous decapods deposited in the National Museum in Prague revealed that all supposed specimens of the lobster genus Oncopareia found in the Middle Coniacian calcareous claystones of the Březno Formation, including one of the Fritsch’s original specimens of Stenocheles parvulus, actually belong to Ctenocheles. This material together with newly collected specimens from the same locality, allowed for erection of a new species, Ctenocheles fritschi. Its major chela possesses a serrated ischium and ovoid, unarmed merus; therefore, it is considered a close relative of the extant C. collini and C. maorianus. Ctenocheles fritschi sp. nov. represents the first report on the occurrence of the genus from the Bohemian Cretaceous Basin. It is one of the oldest records of Ctenocheles and simultaneously one of the best preserved fossils of the genus reported to date. Confusing taxonomy of S. parvulus is reviewed and shortly discussed.

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Budil P, Manda Š, Tetlie OE; Vol. 89, issue 2, pages 257 - 267The eurypterid record from the Prague Basin includes occasional Ludlow faunas, but in the uppermost Silurian (Přídolí) eurypterids suddenly become common in relatively deep water facies. Pterygotids clearly dominate these late Silurian faunas, whereas carcinosomatids are represented by the single species Eusarcana acrocephala, known from only a few specimens. This species is revised and its validity is discussed herein. A new eurypterid fauna found in deep water shale facies is described from the lower and middle part of the Motol Formation, Wenlock, Sheinwoodian-Homerian, Cyrtograptus murchisoni to C. lundgreni graptolite biozones, at Praha-Lochkov. It consists of common fragments of the carcinosomatid eurypterid described here as Eusarcana? sp. A and rare possible pterygotid fragments. This is the earliest evidence of carcinosomatids outside Laurentia and one of the earliest records of the group worldwide. This early occurrence outside a hypothetical Laurentian evolutionary centre is discussed with respect to the palaeobiogeography of other faunas colonising peri-Gondwanan basins after the decline of widespread early Silurian anoxia. A previous suggestion that carcinosomatids (presumed basal members of the Carcinosomatoidea) had similar distribution patterns to pterygotoids is discussed. Eurypterids migrated into the peri-Gondwanan realm from the tropical zone, but the dispersion potential of carcinosomatids into the temperate and cool water realm was probably lower than that of pterygotids. In the Prague Basin, the carcinosomatid-dominated fauna of the Wenlock age was replaced in the late Silurian by a pterygotid-dominated fauna.

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Lerosey-Aubril R, Hegna TA, Babcock LE, Bonino E, Kier C; Vol. 89, issue 2, pages 269 - 282The Guzhangian Weeks Formation (House Range, Utah, USA) contains a virtually unstudied but diverse assemblage of "soft-bodied" organisms. This fauna includes several enigmatic appendages of arthropods that are described in this contribution. Six appendages (two isolated and four paired appendages) are interpreted as frontal appendages of a probably new species of Anomalocaris. They are characterized by a slender morphology, 14 podomeres, ventral spines alternating in size, up to three auxiliary spines per ventral spine, and only two dorsal spines. Another isolated appendage is also tentatively assigned to Anomalocaris, but it exhibits a more robust morphology, a stronger distal tapering, and apparently simple ventral spines, suggesting that it may represent a distinct taxon. These frontal appendages represent the youngest occurrence of anomalocaridids in Laurentia and demonstrate the persistence of older, Burgess Shale-type taxa in the Weeks Formation. An assemblage of four antenniform and six robust and heavily-armed appendages is also described. These are interpreted as the serially arranged, anterior appendages of a single individual of an undetermined arthropod species. This association of three pairs of robust, spiny appendages with two pairs of antenniform structures in a Cambrian arthropod is unique.

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Esteve J, Zamora S; Vol. 89, issue 2, pages 283 - 291Enrolled agnostids have been known since the beginning of the nineteenth century but assemblages with high number of enrolled specimens are rare. There are different hypotheses about the life habits of this arthropod group and why they enrolled. These include: a planktic or epiplanktic habit, with the rolled-up posture resulting from clapping cephalon and pygidium together, ectoparasitic habit or a sessile lifestyle, either attached to seaweeds or on the sea floor. Herein we describe two new assemblages from the middle Cambrian of Purujosa (Iberian Chains, North Spain) where agnostids are minor components of the fossil assemblages but occasionally appear enrolled. The taphonomic and sedimentological data suggest that these agnostids were suddenly buried and rolled up as a response to adverse palaeoenvironmental conditions. Their presence with typical benthic components supports a benthic mode of life for at least some species of agnostids.

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Laibl L, Fatka O, Crônier C, Budil P; Vol. 89, issue 2, pages 293 - 309Preservation of ontogenetic stages of trilobites from the Cambrian of the Skryje-Týřovice Basin (Barrandian area) has been known from several localities in the upper part of the Buchava Formation. The most complete information on exoskeletal changes during ontogeny was based on material assigned by Barrande (1852) to Sao hirsuta. Based on quantitative methods and detailed study of the morphology of the exoskeleton, we recognize three protaspid and two early meraspid instars of Sao hirsuta. We also describe the protaspid stages of two indeterminate taxa of Ptychopariida, one originally determined as the protaspides of Sao hirsuta and the other referred to by Růžička (1943) as “Barrande’s larva”. Protaspides of Sao hirsuta have an adult-like morphology, and their presumed benthic mode of life is consistent with the restricted palaeogeographic distribution of this genus.

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Schoenemann B, Clarkson ENK, Castellani C, Waloszek D, Maas A, Meyer-Rochow VB; Vol. 89, issue 2, pages 311 - 324The exceptionally good preservation of phosphatised, three dimensionally preserved “Orsten” arthropods permits insight into the internal morphology of ancient compound eyes. Analysis, presented here, of the stalked eyes of a Cambrian “Orsten” crustacean reveals structures such as a cornea, a crystalline cone, rhabdomers belonging to possibly five or six sensory cells and an absence of a gap (known as the clear-zone) between dioptric structures and the retina. All these features collectively suggest that this compound eye is of the apposition type. Thus, the principle of mosaic vision likely dates back to Cambrian times, more than half a billion years ago. Using well-established methods this eye can be characterised as dim-light adapted and is likely to have belonged to a benthic organism like many others known from fossils of the Cambrian Alum Shale of Sweden. This seems to be one of the oldest known apposition eyes, and the structural differences between it and eyes more closely conforming to the tetraconate system are likely to be related to the small size of the eye and the photic environment in which it had to operate. Differences from typical compound eye organisation, such as for instance a smaller number of retinula cells than the more typical eight found in most tetraconate arthropods, suggest that either the tetraconate system is not basal and universal, as is often assumed, or that modifications to the system enabling the eye to improve photon capture had already occurred during the Cambrian.

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Budil P, Fatka O, Rak Š, H&Ouml, rbinger F; Vol. 89, issue 2, pages 325 - 334Rare remains of Reussiana cf. brevispicula Hörbinger, 2000 have been collected near the Praha-Lochkov, together with a rich faunal association characteristic of the upper part of the Lochkov Formation (Lower Devonian, Lochkovian, Monograptus hercynicus graptolite Biozone). This occurrence confirms the earlier assumption that large Devonian dalmanitids (“odontochilinids”) appear in the Prague Basin below the Basal Pragian Regressive Event. The unique discovery represents one of the earliest occurrences of Devonian dalmanitids worldwide and sheds light on the migration and early radiation of dalmanitids within the Rheic Ocean realm during the Early Devonian.

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Pegel TV; Vol. 89, issue 2, pages 335 - 345The Diringde reef complex (Kotuy River Basin, Southwest of the Anabar Region, northern Siberian Platform, Russia) has formed during the late mid-Cambrian-early Furongian at the shelf margin of the epicontinental marine basin. Two detached carbonate buildup complexes originated. The southern mid-Cambrian buildup complex is replaced laterally by shale-carbonate rocks of the open basin slope. The northern mid-Cambrian-Furongian buildup complex passes laterally into the inner shelf dolomites. The trilobite associations of the central parts of both buildup complexes consist of rare endemic polymerids, distributed mainly in interbeds between algal buildups. The trilobite associations in narrow facial transition zones (reef flanks) to surrounding stratified deposits differ in having more abundant polymerids, higher taxonomic diversity, and include also agnostoids. The trilobite associations are similar to the assemblage of the reef-dominated mid-Cambrian-Furongian Chukuka Formation that is widespread in the neighboring South Anabar Region. The associations from the reef flank of the southern buildup complex consist mainly of species distributed in Cambrian shallow- water deposits of the Saami, Sakha, Nganasany and Tavgi horizons in the Kulyumbe River reference section, northwestern Siberian Platform. The trilobite assemblages of deeper water deposits of the Eyra Formation that are found on the open marine side of the Diringde reef complex combine typical elements of mainly endemic, shallow-water associations of the southern buildups and the slope basin associations with various cosmopolitan pre-Furongian agnostoids enabling international correlations.

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Bushuev E, Goryaeva I, Pereladov V; Vol. 89, issue 2, pages 347 - 364Possibly the most ancient trilobites on the Siberian platform, belonging to the the Superfamily Fallotaspidoidea, were collected 36 m above the base of the middle Tyusser Formation, traditional lower Cambrian (Global Stage 3), in the Ulakhan-Aldyarkhai Creek section on the northern edge of the Cambrian Yudoma-Olenek sedimentary basin. These trilobite remains are probably slightly older that the first occurence of Profallotaspis jakutensis Repina, 1965 at other localities. Profallotaspis tyusserica sp. nov., although an olenellid, is characterised, among other features, by the “facial lines” that are possible incipient facial sutures, present anteriorly of ocular lobes and crossing the anterior margin of the cephalon. The occurrence of Profallotaspis tyusserica sp. nov. in the section is referred to the Profallotaspis Zone. The trilobites from the Pagetiellus anabarus-Nevadella Zone of the Cambrian Stage 3 were found 14.2 m above the FAD of Profallotaspis

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Rábano I, Gutiérrez-Marco JC, García-Bellido DC; Vol. 89, issue 2, pages 365 - 374Illaenid trilobites were relatively scarce in south-polar peri-Gondwanan areas during the Ordovician, with all their African occurrences restricted to the Middle and Upper Ordovician of Morocco. At a specific level, only the Bohemian form Ectillaenus benignensis (Novák) has been positively identified from the Middle Ordovician of that region. In the present work we add the discovery of the new form Caudillaenus nicolasi gen. et sp. nov., occurring in a single bed of late Darriwilian 2 age within the Taddrist Formation of the Rahiat region (south of Alnif), in the central Moroccan Anti-Atlas. The new genus is characterized by a large and subtriangular pygidium, a cephalon with relatively large eyes, a broad rostral plate with a short upwardly and forwardly turned posterior flange, and a globose hypostome. It shows a spheroidal enrolment type previously unknown in illaenids, with the pygidium protruding beyond the cephalon, and the cephalic margin fitting into a shallow and wide coaptative furrow on the pygidial doublure.

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Geyer G, Peel JS, Streng M, Voigt S, Fischer J, Preu&szlig, e M; Vol. 89, issue 2, pages 375 - 400Early Middle Cambrian bituminous coquinoid limestones from a tectonically isolated outcrop in southwestern Kyrgyzstan yield a remarkably diverse fauna, with stem-group cnidarians, trilobites, rhynchonelliformean brachiopods, and other shelly fossils. The fossil site is in the northern foothills of the Turkestan Range and thus forms part of the westernmost extension of the South Tien Shan. The fauna includes two fairly well known trilobite species, Glabrella ventrosa Lermontova, 1940 and Dorypyge richthofeniformis Lermontova, 1940, that provide confident support for an Amgan age of the rocks. New described taxa include the stem-group cnidarian Cambroctoconus kyrgyzstanicus Peel sp. nov., the trilobite Olenoides sagittatus Geyer sp. nov., and the helcionelloid Manasoconus bifrons Peel gen. et sp. nov. Additional fossils within the samples include the trilobites Olenoides sp. A, Kootenia sp., and Pseudoeteraspis? sp.; the rhynchonelliform brachiopods Narynella cf. ferganensis (Andreeva, 1962), Narynella? sp., Austrohedra? sp. nov., and two species of uncertain generic affinity; the tommotiid Tesella sp.; the hyolithelminth Hyolithellus sp.; and the palaeoscolecid Hadimopanella oezgueli Gedik, 1977. Of particular interest is Cambroctoconus kyrgyzstanicus with an octagonal corallum and a sparsely septate calyx.

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Mergl M; Vol. 89, issue 2, pages 401 - 412A new association of odontopleurid trilobites is described from calcareous claystone to marlstone, the so-called “Perník Bed”, of the topmost part of the Králův Dvůr Formation. The association includes Diacanthaspis krizi sp. nov., associated with Bojokoralaspis peregrina (Barrande, 1872) and other rare and poorly known odontopleurids preliminary referred to Chlustinia Přibyl & Vaněk, 1965, Proceratocephala Prantl & Přibyl, 1949 and Eoleonaspis Sheng, 1974. This association indicates a closer relationship to the late Katian and early Hirnantian odontopleurid faunas of Baltica and Avalonia than to those of Armorica (Spain, Sardinia), where the genera Calipernurus Whittington, 1956a, Diacanthaspis Whittington, 1941, Dicranurus Conrad, 1841, Hispaniaspis Hammann, 1992, Radiaspis Richter&Richter, 1917, and Whittingtonia Prantl&Přibyl, 1949 are present in carbonatic buildups of the late Katian age. It is assumed that the deposition of “Perník Bed” is a result of the early Hirnantian sea level lowering and not of the warming related to the Boda event.

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Fatka O, Szabad M; Vol. 89, issue 2, pages 413 - 429Previously published biostratigraphical subdivisions of the “middle” Cambrian succession of the Příbram-Jince Basin in the Barrandian area are summarized and a modified subdivision of twelve biozones proposed. Nine of the biozones are delimited by the first appearance of the eponymous species; five of these are interval zones and four are taxon-range zones. The youngest stratigraphical levels of the fossiliferous sequence in the Litavka River Valley, which lack any characteristic taxa, are assigned to one assemblage zone that is subdivided into two levels defined by the presence of two trilobites and two lingulate brachiopods. The Kodymirus vagans, Hypagnostus parvifrons and Dawsonia bohemica zones, and the Barren interzone between Paradoxides (Eccaparadoxides) pusillus-Paradoxides (Paradoxides) paradoxissimus gracilis, are newly established; the other zones are redefined or the earlier definitions retained.

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Pärnaste H, Bergstr&ouml, m J; Vol. 89, issue 2, pages 431 - 450Recent revision of the Ölandian trilobite faunas in Baltoscandia and the Ural Mountains throws new light on the development of the trilobite faunas in Baltica and possible migration links to surrounding terranes. The trilobite assemblages of 104 genera on the Uralian side of Baltica show different development patterns for the south and north through the Tremadocian to the Darriwilian. The oldest Uralian trilobites - disputably of latest Cambrian or earliest Ordovician age - arrived probably from the Siberian and Kazakh terranes being represented by mostly endemic genera such as Kujandaspis and Jdyia, but also with pandemic Akoldinioidia and Micragnostus. The following Kidryasian, Kolnabukian and Kuagachian faunas change gradually to show increasing difference between the sections in the South Urals and those in the northern Polar Urals or Pay-Khoy. In Kidryasian the olenids dominate in the South Urals as they do in many other regions during the early Tremadocian. The Kolnabukian trilobites represent the most diverse trilobite association in the region, and are comparable to the Ceratopyge fauna. The Kuagachian fauna contains a few additional elements, increasing the difference between south and north but with reduced generic diversity. The routes of faunal exchange are modified too. Thus during the Early Ordovician migration between the Uralian side of Baltica and the Baltoscandia, Kazakh and Altai-Sayan terranes becomes more important than that between the Uralian side of Baltica and the Siberia, North and South China plates. The Darriwilian Karakoľ-Mikhailovskian faunal association shows a clear separation between north and south Urals with the former region, as in Baltoscandia, dominated by asaphids, while in south a reefal illaenid-cheirurid association of Laurentian genera occurs. This is rather intriguing given the widely accepted palaeogeographical disparate position and latitude of Laurentia at the time.

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Rodríguez-Tovar FJ, Reolid M; Vol. 88, issue 4, pages 697 - 712A geochemical analysis has been conducted in the Fuente de la Vidriera section of the External Subbetic (Betic Cordillera, southern Spain) in order to interpret the incidence of the Toarcian Oceanic Anoxic Event (T-OAE) in the westernmost end of the Tethys. The obtained values of detrital, redox and palaeoproductivity proxies throughout the succession show minor fluctuations, but only punctual significant changes. Detrital input is nearly constant during the studied interval, except punctually in the lower part of serpentinum Zone, characterized by an increase in both fluvial and eolian detrital transport. Associated to this local higher fluvial and eolian activity, a comparatively higher concentration of organic matter is punctually registered, as revealed by the comparatively highest total organic carbon (TOC) value (0.99 wt.%). The remaining part of the section shows TOC values in the lower range of those registered in the Tethyan Toarcian sections (< 0.4 wt.%). The obtained ratios of redox-sensitive trace metals lead to the interpretation of oxic to dysoxic bottom-waters, with a singular sharp decrease in oxygenation corresponding to a short interval within the serpentinum Zone (sample FV-18) correlated to the T-OAE. The minor incidence of the T-OAE registered in this westernmost end of the Tethys, in which punctual dysoxic conditions are restricted only to a decimetre-scale interval reveals the importance of regional context and local oceanic-atmosphere dynamics on the local record of this phenomenon.

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Van Iten H, Muir LA, Botting JP, Zhang YD, Lin JP; Vol. 88, issue 4, pages 713 - 722Conulariella sp. and possibly one other conulariid species occur in close association with Sphenothallus sp. in the lower part of the early Floian Tonggao Formation near the town of Sandu, Guizhou Province, China. This is the only known occurrence of Conulariella in Early Ordovician rocks outside of Bohemia (Perunican terrane), and also the first report of Sphenothallus from the Ordovician of China. The apertural margin of Conulariella appears to have been mostly straight, and apertural lappets probably were not present in this genus. Some Tonggao conulariids may have attached to orbiculoid brachiopods in life. Based on the most recent palaeogeographical reconstructions of Gondwana and associated terranes, Conulariella could have had a dispersal path along the Gondwanan margin.

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Schulbert C, Nützel A; Vol. 88, issue 4, pages 723 - 778A rich gastropod fauna is decribed from the Early/Middle Jurassic boundary (late Toarcian/early Aalenian) of Franconia (N Bavaria, South Germany). It comprises 35 nominate species and additional 9 species are treated in open nomenclature. With a few exceptions, the studied material comes from the Jurensismergel and the Opalinuston formations of the Mistelgau clay pit near Bayreuth. These sediments represent marine soft bottom environments. Gastropods are the most diverse and the most abundant group of the benthic communities in the Mistelgau clay pit. Bivalves, ophiurid and crinoid ossicles as well as foraminifera are also abundant. Among the bivalves, the paper pecten Bositra buchi and the inoceramid Pseudomytiloides dubium are especially abundant. Most of the members of the benthic fauna are small (< 15 mm) or even minute. Only the bivalve Pseudomytiloides dubium, some of the vetigastropods (e.g., Pleurotomarioidea) and the family Gordenellidae (Turritelloidea and Proacirsa) attain a size larger than 2 cm. However, these large species are rare. The most abundant gastropods are the caenogastropod species Coelodiscus minutus and Toarctocera subpunctata. Both species are especially abundant in the lowermost portions of the sampled section. Towards the Aalenian, an increase in diversity can be observed. This reflects recovery from the late Pliensbachian/early Toarcian extinction event. This event was connected with early Toarcian anoxia in Central and Northern Europe including black shale deposition (Posidonienschiefer). The studied gastropod fauna lived during still impoverished but improving environmental conditions. The relatively high diversity and abundance of the benthos suggest aerobic or dysaerobic conditions, however with possible fluctuations of oxygen concentrations. The fauna was also constrained by soft bottom conditions. 12 species are described as new: Mistelgauia monarii, Hummelgauia microstriata, Jurilda zapfi Schulbert, Nützel & Gründel sp. nov., Franconicilda juliae, Carinathilda? dieneri, Conusella convexa, Cossmannina eggmaieri, Sinuarbullina? mistelgauensis, Striactaeonina waltschewi Schulbert, Nützel & Gründel sp. nov., Striactaeonina richterorum Schulbert, Nützel & Gründel sp. nov., Parvulactaeon imprimum Schulbert, Nützel & Gründel sp. nov. and Parvulactaeon inclinatum Schulbert, Nützel & Gründel sp. nov. Three genera are described as new: Hummelgauia, Mistelgauia and Franconicilda. The family Coelodiscidae Gründel&Nützel fam. nov. is described as new based on the probably holoplanktonic gastropod genus Coelodiscus.

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Haug JT, Leipner A, Wappler T, Haug C; Vol. 88, issue 4, pages 779 - 791We report fragmentary specimens from the Piesberg quarry (Upper Carboniferous, Northwestern Germany) that represent exuviae of nymphal blattoids (Dictyoptera). Most of the remains are isolated abdomina, one specimen also preserves a wing pad. The specimens document two developmental stages and include the smallest Palaeozoic blattoid nymph found to date. The specimens from the Piesberg quarry closely resemble other Palaeozoic blattoid nymphs, for example, specimens from the famous Mazon Creek Lagerstätte (Upper Carboniferous, Illinois, USA), at least as far as external morphology is concerned. As for preservation, the specimens from the Piesberg quarry show strong resemblance to specimens from the Lower Permian Elmo Lagerstätte (Kansas and Oklahoma, USA). The two Lagerstätten, although differing in age, appear therefore to be interesting candidates for a palaeoecological comparison. The find of immature insects at the Piesberg quarry is another example of fossilised development in arthropods from this Lagerstätte, other examples are known from Euproops, Arthropleura and Aphantomartus pustulatus

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Frank J, Wilmsen M, Košťák M; Vol. 88, issue 4, pages 793 - 812The endemic Late Cretaceous nautilid genus Deltocymatoceras Kummel, 1956 is represented by Deltocymatoceras leiotropis (Schlüter, 1876) and D. rugatum (Fritsch Schlönbach, 1872). Characteristic for this genus is a bulbous involute shell with strong radial ribbing and a ventral keel, which appears in post-juvenile ontogenetic stages. The combination of these morphological features is unique among post-Palaeozoic nautiloids. Both species are restricted to the Late Turonian–Middle Coniacian of Central Europe and England. Until now, the type species D. leiotropis was known based only on the holotype specimen. This specimen is re-described with revised occurrence and for the first time photographically illustrated. The only preserved syntype from the type specimens of D. rugatum was re-discovered during this revision and more than thirty other specimens were studied. Representatives of Deltocymatoceras show clear morphological changes during their ontogeny and acquisition of maturity, most notably the appearance of a ventral keel in premature stages and its disappearance at maturity. The hypothesis of a close phylogenetic affinity of Deltocymatoceras to the genus Cymatoceras Hyatt, 1884 is based on similar morphological features such as the suture, ribbing, shell shape and early ontogenetic development. The ventral keel is quite an exceptional feature of morphology in post-Palaeozoic nautiloids. In particular the combination with an involute depressed shell is only shared with representatives of the genus Angulithes Montfort, 1808 (Cretaceous–Palaeogene) and Gryponautilus Mojsisovic, 1902 (Triassic). The combination with a compressed and evolute planispiral shell is more common in Palaeozoic and some post-Palaeozoic nautiloids. The ventral keel is discussed here in relation to its functional aspects (hydrodynamic stability) in combination with the strong radial ribbing (protection of the shell against mechanical damage). The appearance of the genus concurred with the late Turonian shallowing/cooling associated with the “Hyphantoceras Event” and the availability of an ecologic niche (i.e., absence of medium-sized, keeled ammonites at that time). Low abundance, an endemic occurrence, and the very short stratigraphic range of the genus (~3.5 Ma) reflect the limited evolutionary success of the Deltocymatoceras lineage.

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