The biostratigraphic and palaeoenvironmental significance of Lower Cambrian (Botomian) trilobites from the Ak-Kaya section of the Altai Mountains (southern Siberia,Russia)

The presence of one of the oldest records of polycystine Radiolaria in the Lower Cambrian sedimentary sequence of the Ak-Kaya section (Gorny Altai) requires a biostratigraphic dating. The trilobites found recently a few tens of meters below the radiolarian-bearing level belong to Calodiscus resimus Repina, Serrodiscus fossuliferus Repina and Alacephalus aff. contortus Repina; they suggest that this part of the Shashkunar Formation can be correlated with the lower part of the Botomian stage. The absence of eyes in the two former species suggests a mode of life buried in the fine pelagic sediments. Indications of the presence of a strongly developed musculature on the third species point to a palaeoenvironment characterized by a relatively high hydrodynamic regime.     

The oldest Lingulids of the Siberian Platform: Microornamentation and shell structure

New brachiopod genus of the order Lingulida Sukharilingula with new type species S. luchininae is described from the Lower Botomian (Lower Cambrian) of northwestern Siberian Platform, basin of the Yenisei River, section on the Sukharikha River. The study of the microornamentation and shell structure of the new genus revealed that the initial shell structure of lingulid shells could transform in the course of early diagenesis. The importance of reconstruction of burial conditions of the valves for the reconstruction of posthumous transformations is discussed.     

Trilobites from the lower and lowermost middle Cambrian of the Kiya River reference section (Kuznetsk Alatau)

The Kiya River reference section is characterized by trilohites confined to units X–XV of the Lower Cambrian Usa Formation and to the base of the lowermost Middle Cambrian Berikul Formation. Trilobites are represented by 130 species assigned to 77 genera. The given paper describes 38 species belonging to 27 genera. 16 species, 2 genera and one subfamily are new. All of them occur in the Usa Formation and in the Lower Cambrian pebbles of the Berikul Formation. Biostratigraphic analysis shows that the trilobite fauna contains characteristic trilobite assemblage elements of the Lower Cambrian regional stages in the Altay-Sayan Fold Belt, i.e. the Kiya and Kameshki regional stages (Atdabanian Stage), the Sanashtykgol regional stage (Botomian Stage), the Obruchev regional stage (Toyonian Stage). Table I shows trilobite species composition and vertical distribution in the reference section.     

On the genus Auricullina Vassiljeva, 1998 and shell pores of the Cambrian helcionelloid mollusks

The genus Auricullina Vassiljeva, 1998 and its type species A. papulosa Vassiljeva, 1998 are redescribed based on new well-preserved material, which allows me to revise the generic diagnosis and greatly add to the morphological characterization of the type species. A new species, A. granulosa sp. nov., is described from the Botomian of Australia. The synonymy of the taxa is improved. The morphology and function of shell pores in Cambrian univalved mollusks are discussed.     

Shell structure of <Emphasis Type="Italic">Kutorgina</Emphasis> Billings (Brachiopoda,Kutorginida)

Shell structure in members of the genus Kutorgina, Lower Cambrian brachiopods with calcareous shells and primitive articulation, is described for the first time. This type of shell structure resembles that of the Lower Cambrian mollusks and hyoliths rather than of brachiopods.     

Lower Cambrian (Atdabanian/Botomian) Shallow-Marine carbonates of the Görlitz Synclinorium (Saxony/Germany)

Summary Geological, papaeontological and microfacies studies in the Lower Cambrian carbonate complex of the G?rlitz Synclinorium (eastern Germany/Saxony/Lusatian region) provide new data for the fossil content, depositional history and palaeogeography. The Lower Cambrian of the G?rlitz Synclinorium belongs to the facies zones 5, 7 and 8 ofWilson (1975)-platform rim with connections to the open ocean and to the restricted platform areas. An extraordinarily rich fauna was found with elements which are in some cases new for Europe (Rhombocorniculum cancellatum Cobbold,Fordilla sibirica Krasilova, Calodiscus lobatus Hall,Archaeooides granulatus Qian,Archiasterella pentactina Sdzuy,Allonia sp.,Obliquatheca aldanica Sysoiev,Conotheca circumflexa Missarzhevsky,Microcornus elongatus Missarzhevsky,Lenalituus sp.,Pelagiella cf.lorenzi Kobayashi,Beshtashella sp.,Comluella sp.,Cambroclavithidae gen. et sp. indet., Helcionellidae gen. et sp., indet. Eocrinoidea gen. et sp. indet.) This fauna indicates Lower Cambrian (higher Atdabanian/Botomian) age and reveals palaeobiogeographical connections to the Siberian Platform, to the Mediterranean area and to China. A somewhat new stratigraphical subdivision of the Lower Cambrian sequence (Zwetau Formation) is described. New units are established within the Ludwigsdorf Member (the carbonatic lower part of the sequence), the ‘Lower Ludwigsdorf Member’ (massive dolostone) and the ‘Upper Ludwigsdorf Member’ (bedeed limestones and their equivalents). The subsequentLusatiops Member is subdivided intoSerrodiscus Bed (claystones) andLusatiops Bed (siltstones).     

Retrograde evolution of Albaillella during the Permian-Triassic crisis

In the present paper, we discuss the evolution of an upper Permian anagenetic lineage of polycystine radiolarians belonging to the genus Albaillella. This genus is characterized by increasing curvature of the shell during the upper Permian and the trend is reversed (proteromorphic retrogradation) in the Lower Triassic with the sudden appearance of forms that are homeomorphic to the earliest Permian representative of the genus. These primitive-looking forms are derived from their immediate ancestors by retrograde evolution, a phenomenon which has been described as proteromorphosis.     

New data on the morphology of ancient gastropods of the genus Aldanella Vostokova, 1962 (Archaeobranchia, Pelagielliformes)

The position of attachment of the shell muscle is discovered in the columellar area of the shell of the Early Cambrian univalved genus Aldanella (family Aldanellidae, order Pelagielliformes, subclass Archaeobranchia), the structure of its protoconch is described, and the presence of series of septa in the embryonic part of their shell is confirmed. These new features confidently support the position of the family Aldanellidae within the gastropod class and allow them to be considered ancestral to younger gastropod lineages with a turbospiral shell.     

A first report of Sphenothallus Hall, 1847 in the Cambrian of Variscan Europe

Ten specimens of two phosphatic fossils have been recently discovered in lower and middle portions of Middle Cambrian Jince Formation in the Czech Republic. They are attributed to the genus Sphenothallus Hall, 1847 and described as two separate species; comparatively small conchs are described as S. kozaki sp. nov., the much larger specimens characterized by its smooth and partly flexible organo-phosphatic walls of shell are determined as ?S. kordulei sp. nov. Sphenothallus is known to range from Cambrian to Permian and accommodates numerous species. However, its Cambrian distribution is considerably restricted. Generally rare specimens have been described from Lower to Middle Cambrian of Laurentia and from the Lower Cambrian of Gondwana and peri-Gondwana. The new record of Sphenothallus from the Jince Biota represents a notable extension of their geographic range.     

Structure of shell muscles in the Cambrian gastropod genus Bemella (Gastropoda: Archaeobranchia: Helcionellidae)

Zones with peculiar microornamentation interpreted as muscle scars were found on the internal molds of the Early Cambrian gastropod genus Bemella Missarzhevsky, 1969 (family Helcionellidae). Shell muscles of helcionellids are reconstructed based on the topographic pattern of muscle scars, i.e., the pedal, cephalic, and mantle retractors are recognized. The reconstruction proposed here of the shell musculature corroborates affinity between ancient gastropod and helcionelloid mollusks.     

Light and electron microscopic observations of the reproductive swarmer cells of nassellarian and spumellarian polycystines (Radiolaria)

We observed reproductive swarmer cells of the nassellarian and spumellarian polycystine radiolarians Didymocyrtis ceratospyris, Pterocanium praetextum, Tetrapyle sp., and Triastrum aurivillii using light, scanning and transmission electron microscopy. The swarmer cells had subspherical to ovoid or spindle shapes with two unequal flagella tapered to whip-like ends. The cell size was approximately 2.5–5.5 μm long and 1.6–2.2 μm wide, which is significantly smaller than that of the collodarian (colonial or naked) polycystine radiolarians. Transmission electron microscopy revealed that the swarmer cells possessed a nucleus, mitochondria with tubular cristae, Golgi body, and small lipid droplets in the cytoplasm; they also had a large vacuole in which a single crystalline inclusion (approx. 1.0–1.5 μm) that was probably celestite (SrSO₄) was enclosed. The swarmer cells were released directly from the parent cells. At that time, morphological change such as encystment was not observed in the parent cells, and the axopodia remained extended in a period of swarmer reproduction for floating existence. This may have prevented the polycystine swarmers from rapidly sinking down to great depths. Thus, we concluded that the polycystine radiolarians release the swarmer cells into the photic layer in the same way as the symbiotic acantharians.     

A Stem Group Brachiopod From The Lower Cambrian: Support For A Micrina (Halkieriid) Ancestry

The shell structure of the Lower Cambrian Mickwitzia , a bilaterally symmetrical bivalve hitherto doubtfully assigned to the Brachiopoda, confirms that the genus shares characters with linguliform brachiopods. The columnar lamination of its organophosphatic shell is homologous with that characterizing acrotretides. The shell, however, is also pervaded by striated apatitic tubes indistinguishable from those permeating the sclerites of the problematic organophosphatic, laminar–shelled Micrina which is close to Halkieria . No crown group brachiopods have such tubes that are presumed to have contained setae. The presence of both these features in the Mickwitzia shell suggests that the stock is a stem group brachiopod with a halkieriid ancestry.     

Ultrastructural and molecular characterization of cyanobacterial symbionts in Dictyocoryne profunda (polycystine radiolaria)

Cyanobacterial symbionts were detected in the extracytoplasm of the polycystine radiolarian Dictyocoryne profunda Ehrenberg. The bacterial symbionts were observed as numerous spherical bodies ~0.5?C1.0???m in diameter under transmission electron microscopy. They were present in a very restricted location close to the periphery of the host radiolarian shell, adjacent to the central capsular wall. Several cells of them may have been in the process of cell division or just divided. The symbionts had thylakoid-like structures, which ran around the cell periphery in two or three concentric layers. Based on the small subunit ribosomal DNA (16S rDNA) phylogenetic analyses, the intracellular symbiotic bacteria grouped with cyanobacteria belonging to the genus Synechococcus. Three sequences, one from each of three specimens of D. profunda, collected in March/October 2009 and March 2010 from the East China Sea, were the same and branched within Synechococcus clade II, that is characterized by strains with low amounts of phycourobilin (PUB).     

Wandel der Vorstellungen von der Frühevolution der Mollusken,besonders der Gastropoda und Cephalopoda

The ancestors of the molluscs are still unknown. Arguments in favour of flatworm-relationship are just as valid as those proposing segmented annelid-like worms as their closest relatives. The earliest molluscs lived before the onset of the Cambrian; but only at the end of this period the now existing classes of conchifers made their first appearance. Early and Middle Cambrian molluscan fossils are problematic. The hyoliths, for example, show relations to such fossils asSalterella andVolborthella, while closest living relatives can be found among tube-building annelids. Scars produced by tissue attached to the shell are of no use in the reconstruction of molluscan phylogeny, but a very useful tool in the analysis of the function regarding the body in interaction with its shell. The ontogenesis of the shell and muscles attached to it in recentFissurella (archaeogastropod) is presented as an example. Well known ontogenies in recent molluscs can aid to the reconstruction of fossils, demonstrated by some fossil gastropods. The interaction of soft and hard tissues, the function and structure of the shell of recent molluscs enables us to interpret the fossil forms, as for example the Lower Devonian coleoid cephalopods from the Hunsrück Schiefer. Reconstruction of the course of evolution is only possible, if information on living molluscs is integrated into historical data provided by the fossils.     

Shell microstructure and imprints of cells of the outer mantle epithelium of <Emphasis Type="Italic">Monticlarella</Emphasis> Wisniewska (Brachiopoda: Rhynchonellida,Norelloidea)

The shell microstructure of the genus Monticlarella Wisniewska, 1932 is studied for the first time, with the species M. nova (Karakash, 1907) and M. lineolata (Phillips, 1835) from the Upper Hauterivian–Lower Barremian of Crimea being used as an example. It is shown that there is a strong similarity between the shell structure of this genus and another representative of the family Norellidae, Suiaella, thus supporting the possibility of using the shell microstructure as a diagnostic feature of the family Norellidae.     

A new rhynchonelliform brachiopod Longtancunella with soft-part preservation from the Hongjingshao Formation (Cambrian Stage 3) in Yunnan,South China

Rhynchonelliform brachiopods made their first appearance in early Cambrian, and became a major group within the palaeozoic evolutionary fauna since late Cambrian. Exceptionally preserved fossils from the early Cambrian Lagerstätten provide valuable chances to investigate their phylogeny and ecology. Longtancunella is one of the most interesting early rhynchonelliforms, and has been mainly recovered from the Chengjiang Lagerstätte (Series 2, Stage 3). Here, we report a new rhynchonelliform Longtancunella xiazhuangensis n. sp. from the lower Hongjingshao Formation (upper Stage 3) in Yunnan Province, China. These specimens were well preserved with soft parts, including pinnate mantle canal system and a pedicle. It is identified as a new species based mainly on its difference in shell ornamentations, pinnate mantle canals and pedicle morphology from the type species. Its pedicle looks unusually stout with distinct annulated lamellae on the surface, and reveals crucial evidence in illustrating its ecology and settling strategy as an early marine epifauna. The ecological interaction between L. xiazhuangensis and other marine animals also provides insights into the food web structure in the early Cambrian.     

Lower Ovetian (Lower Cambrian) trilobites and biostratigraphy of the Pedroche Formation (Sierra de Córdoba, southern Spain)

The low Lower Cambrian rocks from the Sierra de Córdoba, which consist of well exposed mixed facies and abundant fossil assemblages showing long stratigraphic ranges throughout the Pedroche Formation, represent one of the best successions of this age in Europe. The fossil assemblages include diverse Ovetian archaeocyaths, trilobites, small shelly fossils, calcimicrobia, trace fossils and stromatolites. Trilobites are still poorly known, and thus they are the main objective of this work. The trilobites studied originate from three sections. At the Arroyo de Pedroche 1 section, cf. Bigotinella and Bigotinabivallata are replaced towards the top by Lemdadellalinaresae, Lemdadellaperejoni sp. nov. and, finally, by Eoredlichia cf. ovetensis. At the Arroyo de Pedroche 2 section, Lemdadellalinaresae is replaced by Lemdadellaperejoni sp. nov. and Eoredlichia cf. ovetensis, while at the Puente de Hierro section Lemdadellalinaresae, L. aff. linaresae and Serraniaverae occur together. These new biostratigraphic data confirm that the Pedroche Formation, originally defined as a repetitive sequence of four members, contains only two members. The new trilobite discoveries permit the first tentative correlation between the Ovetian of southern Spain and Lower Cambrian strata from the High Atlas (Morocco), Siberia, Antarctica and Carteret (France).     

A Middle and Late Cambrian age for the Booley Bay Formation,County Wexford,Ireland: New acritarch data and its implications

A well preserved Ediacara-type fauna was recorded for the first time a few years ago from the bases of seven sandstone beds in the type section of the Lower Palaeozoic Booley Bay Formation in County Wexford, Ireland. Four microfossil samples from mudstones interbedded with the sandstones yielded an acritarch microflora considered indicative of a late Late Cambrian age for the Ediacara fauna, thus suggesting extension of its range from the Neoproterozoic to the Late Cambrian, rather than to the Middle Cambrian as had been previously suggested. The current study examines the microfossils in more detail, with 18 samples, all of which were productive. One additional Ediacara bed approximately 100 m above those recorded earlier was also observed. The exceptionally well preserved acritarch assemblages indicate a clear Middle Cambrian age for the Ediacara beds, thus predating the previously suggested upper limit for Ediacara faunas. The uppermost part of the formation, above known occurrences of Ediacara beds, is younger; that is, early Late Cambrian, probably coeval with the Olenus trilobite zone. In addition, the age now proposed for the Booley Bay Formation shows that it is part of the Lower Palaeozoic Ribband Group of southeast Ireland, and not part of the Cahore Group as has recently been suggested by the Irish Geological Survey. Thirty-seven acritarch species (or species groups) are distinguished and illustrated. One new species, Stellechinatum ? mariatheresae Vanguestaine, is established.     

Middle Cambrian trilobites from Borehole Nizhny Imbak 219 (northwestern Siberian Platform)

Borehole Nizhny Imbak 219 is situated in the northwestern Siberian Platform. Paleontological material comes from the clayey–limestone series at a depth of 2333.3–2314.3 m referred to the Ovatoryctocara and Kounamkites zones of the Middle Cambrian Amgan Stage and from the overlying limestone series at a depth of 2264.1–2244.0 m referred to the upper part of the Kounamkites Zone and an unnamed zone of the Amgan Stage and also to the Solenopleura patula and Dorypyge olenekensis–Corynexochus perforatus zones of the Middle Cambrian Mayan Stage. The questions of the traditional Lower–Middle Cambrian boundary and the role of Siberian sections in the construction of the International Chronostratigraphic Chart are considered. The trilobites collected are described.