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The ichnology of the Middle Ordovician Winnipeg Formation has been analysed based on the study of cores from five wells drilled in southeast Saskatchewan (Canada). Six sedimentary facies, ranging from upper shoreface to lower offshore settings in a shallow‐marine environment, have been characterized. Ichnological attributes are consistent with those in currently proposed models for shallow‐marine wave‐dominated settings, but ichnodiversity is lower than in post‐Palaeozoic settings. Low ichnodiversity in the Winnipeg Formation most likely reflects evolutionary factors rather than environmental controls. Interestingly, low‐energy, distal deposits of the Winnipeg Formation display intense degree of bioturbation, reflecting a well‐developed mixed layer and underscoring the importance of the Great Ordovician Biodiversification Event in terms of sediment mixing. [ABSTRACT FROM AUTHOR]

It is hypothesized that the contrast observed between different Cambrian and Ordovician diversity trends could be explained by an ecological process linking animal dispersal with speciation and extinction rates. During the Early Ordovician (possibly earlier), local dispersal (within the same region) occurred asynchronously. When dispersal occurred following environmental changes, invading taxa could have triggered the disappearance of specialized ones, that were unable to adapt to these changes, eventually leading to increased extinction rates. Where local dispersal did not occur, the increase in diversity would have not been obscured by extinctions. This complex interplay of events during the Early Ordovician gave rise to intricate diversity patterns in the Middle Ordovician. The Middle Ordovician is characterized by a particular palaeogeographical context favouring speciation during episodes of inter-regional dispersal. Speciation rates would be partially obscured if local dispersal did not occur in the Early Ordovician, as more specialized taxa that survived the Early Ordovician will eventually go extinct during regional Middle Ordovician dispersal. As such, the contrasting diversity trends may be the result of the asynchronicity of dispersal between animal groups and regions during the Cambrian and the Ordovician. [ABSTRACT FROM AUTHOR]

Five quartzose sandstone slabs hosting small groups or mass associations of Anaconularia anomala are described from the Upper Ordovician Letná Formation in the Prague Basin. The slabs contain from 4 to 59, mutually adjacent or contiguous conulariids ranging from 5 to 89 mm in length and situated on a single bedding plane. Associated with the conulariids are small mudstone intraclasts and other fossils, mostly disarticulated brachiopods and trilobites. All 101 studied conulariid specimens are oriented parallel to bedding and show strong preferential alignment, with the apical ends pointing in the same general direction. Sixteen of the conulariids terminate adapically in a probabe schott and/or exhibit a possible internal schott, while five specimens preserve one or two apertural lappets. The investigated conulariids lived in clumps and were buried catastrophically following alignment by unidirectional currents or flows acting on bodies that may have been leaning in the down–current direction and/or which had their center of mass displaced toward their apical end. Neither these nor 3000 additional specimens of A. anomala from the Sandbian Letná and Zahořany formations show any evidence of clonal budding; however, the hypothesis that clumping resulted from asexual proliferation cannot be ruled out. Finally, the periderm of A. anomala was compaction– resistant and smooth, lacking both corrugation (transverse ribs) and nodes, but whether the angular groove present at the facial midline of casts is a mould of a midline sulcus or of an internal carina remains unclear. [ABSTRACT FROM AUTHOR]

Ordovician conodonts have been extensively documented in the Argentine Precordillera, providing a robust database for a diverse set of palaeontological studies. Despite the numerous studies, the published taxonomy and stratigraphical ranges, data remain contradictory for particular time intervals. Data from a new conodont collection from the Gualcamayo Formation exposed at the Cerro La Chilca section, and new information on the occurrence and ranges of species from the Las Chacritas and Las Aguaditas sections are presented herein. We used a computer‐assisted numerical sequencing program (CONOP9) to construct a composite stratigraphical range chart from data of 57 conodont species in four sections from the Argentine Precordillera. The identified zones of Lenodus variabilis, Yangtzeplacognathus crassus, Eoplacognathus pseudoplanus and Eoplacognathus suecicus allowed us to verify and adjust the biostratigraphical scheme for the Darriwilian of the Central Precordillera. Additionally, species of the genera Histiodella, namely Histiodella sinuosa, Histiodella holodentata, Histiodella kristinae and Histiodella bellburnenisis, enable a reasonable correlation between the Histiodella‐based zonation and the Baltoscandian zonation. Conodont diversity is evaluated using conventional measures (total diversity and normalized diversity) and an interval‐free approach with CONOP9 software. Our data show a positive pattern in conodont diversification, increasing rapidly through the L. variabilis to the Y. crassus zones and reaching a peak in the E. pseudoplanus Zone. When analysing diversity fluctuations with respect to the environmental changes within the depositional basin, migrations in and out of the basin related to local sea level fluctuations appear to be an important process driving the conodont diversity pattern in the Precordillera. [ABSTRACT FROM AUTHOR]

A high‐resolution chemostratigraphical (coupled δ13Ccarb and δ18Ocarb) study of the topmost Floian through the middle Darriwilian (Ordovician) succession at the Hällekis quarry, Kinnekulle, southern Sweden, shows relatively steady isotopic values with overall minor changes, although some notable short‐ and long‐term shifts are discernible. A pronounced positive shift in δ13C in the uppermost part of the study succession is identified as the Middle Darriwilian Isotopic Carbon Excursion (MDICE), representing the only named global isotopic excursion in the data set. Regional and global comparisons suggest that few details in the different carbon and oxygen isotope curves can be confidently correlated, but longer‐term patterns appear quite consistent. Trends in the isotope data are in agreement with palaeogeographical reconstructions. Differences in stratigraphical patterns of both carbon and oxygen isotopes between localities suggest strong secular development at several spatiotemporal scales; any global signal involving relatively minor isotopic shifts is often masked/subdued by local and regional overprinting and care should be taken not to overinterpret data sets. Collectively, the data suggest rising sea levels and cooling climates through the studied time interval, but detailed interpretations remain problematic. [ABSTRACT FROM AUTHOR]

Following the appearance of numerous animal phyla during the ‘Cambrian Explosion’, the ‘Great Ordovician Biodiversification Event’ (GOBE) records their rapid diversification at the lower taxonomic levels, constituting the most significant rise in biodiversity in Earth's history. Recent studies suggest that the rapid rise in phytoplankton diversity observed at the Cambrian–Ordovician boundary may have profoundly restructured marine trophic chains, paving the way for the subsequent flourishing of plankton‐feeding groups during the Ordovician. Unfortunately, the fossil record of plankton is incomplete. Its smaller members represent the bulk of the modern marine biomass, but they are usually not documented in Palaeozoic sediments, preventing any definitive assumption with regard to an eventual correlation between biodiversity and biomass at that time. Here, we use an up‐to‐date ocean general circulation model with biogeochemical capabilities (MITgcm) to simulate the spatial patterns of marine primary productivity throughout the Ordovician, and we compare the model output with available palaeontological and sedimentological data. [ABSTRACT FROM AUTHOR]

This study presents a compilation of the temporal distribution of 200 bryozoan genera during the Ordovician. Bryozoans appeared in the earliest Ordovician (Tremadoc), diversified rapidly until the late Sandbian, and then suffered three distinct extinctions in the Late Ordovician. In the early Katian, the first significant extinction eliminated 22.7% of bryozoan genera. That was the highest taxonomic loss in the Ordovician; however, due to high origination rates, the magnitude of this extinction was the lowest among the three extinctions. The second extinction wave occurred in the late Katian, resulting in taxonomic loss of 22.4%. This event can be estimated as the most severe for bryozoans during the Ordovician because of extremely low origination rates what resulted in the highest net decrease of diversity. The third extinction of bryozoans occurred during the Hirnantian resulting in the lowest taxonomic loss (16.5%) and intermediate net decrease of diversity. The diversity dynamics of bryozoans in the Ordovician was apparently controlled by climatic changes, provinciality and food availability. [ABSTRACT FROM AUTHOR]

During the Great Ordovician Biodiversification Event (GOBE), the number of marine invertebrate families more than tripled. Fundamental shifts in clade dominance and ecological structure led to the rise of the Palaeozoic Fauna and the second Palaeozoic Ecological Evolutionary Unit (EEU P2 of Sheehan), which revolutionized benthic ecosystems for the next 200 million years. Although general global signals of increased diversity and ecosystem restructuring are known, direct links between these changes are more poorly constrained on high‐resolution local scales. To address this, rhynchonelliformean brachiopod assemblages of the Middle Ordovician Simpson Group (Oklahoma, USA) were assessed before, during and after maximum local diversity increase related to the second global pulse of the GOBE. Stratigraphically constrained brachiopod species occurrence and abundance data were collected for Dapingian‐lower Sandbian strata via field study. Brachiopod assemblages exhibited declining dominance and increasing evenness from the Dapingian through middle Darriwilian stages followed by high volatility in index values during and after the GOBE interval. These patterns document local faunal turnover and shift from EEU P1 to P2. Furthermore, the average species body volume statistically increased over this interval, a pattern that is independent of phylogenetic constraints. Paired increase in mean body size and size disparity is evidence of niche specialization and utilization of additional food resources. Together, changes in body size, evenness and dominance indicate that increasing ecological complexity was coincident with diversification in Oklahoma. This suggests that a common mechanism, such as climate optimization or increased food abundance, was locally responsible for building both taxonomic diversity and ecological complexity during the GOBE. [ABSTRACT FROM AUTHOR]

The Bohemo-Iberian regional scale for South Gondwana, involving the 'Mediterranean Province', comprises five regional stages (Arenigian, Oretanian, Dobrotivian, Berounian and Kralodvorian) plus the global Tremadocian and Hirnantian. The predominance of shallow-water taxa in those high-latitude faunas imposes serious difficulties for correlating the regional succession with the formal global chronostratigraphy because of the almost total absence of the key graptolites and conodonts defining the base of the standard series, stages and stage slices. Instead, the abundant benthic faunas (trilobites, brachiopods, molluscs, echinoderms) of South Gondwanan origin largely dominated in the area from the middle Darriwilian to the late Katian. The poleward faunal migration of originally Avalonian, Baltic, Laurentian and even Asiatic taxa during the Boda Event of global warming progressively ends with the endemicity in the region, where the ensuing benthic assemblages were severely affected by the Hirnantian glaciation. The regional scale significantly improves the precision of correlations between Ordovician strata from SW and central Europe, North Africa and a large part of the Middle East. An updated record of palaeontological data from areas where Mediterranean faunas remain practically unknown, or are still poorly investigated, is also included. Palaeobiogeographical relationships based on the distribution of faunas across South Gondwana are suggested as an improvement for positioning many territories in modern palaeogeographical reconstructions and offer a constructive approach to problems related to the pre-Variscan and pre-Alpine orogenic puzzles. [ABSTRACT FROM AUTHOR]

The reefs of the Vasalemma Formation, late Sandbian, Late Ordovician, of northern Estonia contain an exceptional rich and abundant bryozoan fauna. They are an example of contemporaneous bryozoan-rich reefs known from around the world, representing the peak diversification interval of this group during the Ordovician. The global Ordovician bryozoan diversification was associated with a decrease in provinciality, a pattern known from other skeletal marine metazoans of this period. The diversification is associated with climatic cooling and increasing atmospheric and sea water oxygenation. However, the mechanisms that led to the bryozoan diversification are poorly known. Here we estimate the bryozoan richness (α and γ diversity) and turnover (β diversity) at the level of samples, reefs, and formations in the Vasalemma Formation and in contemporaneous reef limestone occurrences of the Baltoscandian region. The resulting richness and turnover values differ among the three observational levels and hence are scale dependent. A consistent pattern with lowest between-reef turnover and relatively high between-sample turnover could be detected, reflecting high small-scale (within reef) heterogeneities in lithology and original bryozoan habitat. This is consistent with published work, in which evidence has been presented for small-scale substrate heterogeneity as the most important diversification driver of the Ordovician brachiopod diversification in the Baltoscandian region. The fact that reefs and their local substrate are strongly organism moderated environments sheds light on the potentially important ecosystem engineering role of organisms, such as bryozoans, for the Ordovician diversification. [ABSTRACT FROM AUTHOR]

The precise age of the Winneshiek Shale, a recently discovered Konservat‐Lagerstätte located in a very unusual depositional setting inside the Decorah impact structure, has remained uncertain in the absence of biostratigraphically highly diagnostic fossils. This chemostratigraphical study, based on δ13Corg data from 36 drill core samples through the shale, shows that the age ranges from the upper part of a small unnamed δ13C excursion in the Dw1 Stage Slice of the Darriwilian Global Stage to the lower part of the MDICE excursion in Stage Slice Dw2 of the same stage. This Dw1–Dw2 interval has an isotopic age of ~464–467 Ma. The gradational contact between the Winneshiek Shale and the underlying, rapidly deposited, impact breccia indicates minimal time difference between the impact event and the Winneshiek Shale. New age data show that the Decorah impact event was coeval with the early Darriwilian abnormally high influx of micrometeorites and meteorites recorded in sections in Baltoscandia, Russia and China and that the Decorah crater can be included among the unusually large number of meteorite craters formed during Middle and early Late Ordovician time. As is commonly the case in black shale deposits, the partly uniquely preserved Winneshiek Shale crater fauna is impoverished taxonomically and adds numerically relatively little to the conspicuous and much discussed Darriwilian global biodiversification increase. [ABSTRACT FROM AUTHOR]

The Ordovician biodiversification has been recognized since the 1960s; the term ‘The Great Ordovician Biodiversification Event’, abbreviated by many as the ‘GOBE’, has been used for the past 20 years. The conceptual development and terminology applied to this crucial episode in marine life signify its considerable complexity. The GOBE includes successive biodiversity phases of the pelagic and benthic biotas, possibly decoupled. Put simply, the GOBE can be seen as a sequence of diversifications of the planktonic (late Cambrian–Early Ordovician), level‐bottom benthic (Early–Middle Ordovician) and reef communities (Middle–Late Ordovician), although the boundaries of these ‘events’ are diachronous (as for the entire GOBE), and it is logical to assume that these communities co‐evolved and interacted. The GOBE also includes several Biotic Immigration Events (BIMEs), such as the ‘Richmondian Invasion’ and the ‘Boda Event’, recording the large‐scale dispersal of taxa from one biogeographical area to another. The GOBE is thus the sum of the diversity trends of all individual fossil groups showing rapid increases, diachronously, during different intervals and across different regions. It thus spans the entire Ordovician, capturing the increasing total diversity of marine organisms during the period. The GOBE is not simply one, but many sequential events. [ABSTRACT FROM AUTHOR]

The Ordovician and Silurian of the Baoshan and Mangshi regions in western Yunnan Province, SW China, have long been regarded as being continuous and representative of the Sibumasu terrane. However, our recent biostratigraphical investigations of three Katian to Llandovery sections of predominantly clastic facies reveal a significant, largely correlative disconformity within the Upper Ordovician. These sections include the Laojianshan and Feida Storehouse sections in Baoshan, and the Shaodihe section in Mangshi. In the Baoshan region, the disconformity lies at the base of the overlying Jenhochiao Formation and spans a time interval from earliest late Katian (Dicellograptus complexus Biozone) to early Hirnantian (lower Metabolograptus extraordinarius Biozone), as constrained by the trilobites and brachiopods from the underlying strata and the graptolites from the overlying strata. In the Mangshi region, the disconformity lies at the base of the overlying Wanyaoshu Formation, spanning nearly the entire late Katian (Dicellograptus complexus Biozone to lower Paraorthograptus pacificus Biozone), as constrained by graptolites, trilobites and brachiopods from underlying and overlying beds. A considerably diverse, typical Hirnantia fauna occurs in the Wanyaoshu Formation, which is correlated with the same fauna from the Kuanyinchiao Formation in the Yangtze region, South China, and its equivalents elsewhere. A weathering crust of 10–20 cm in thickness occurs ubiquitously in both regions, in association with the disconformity. This stratigraphical gap within the Upper Ordovician in western Yunnan is probably resulted from the abrupt sea‐level drop induced by Late Ordovician Glaciations, or alternatively and less likely result from a regional tectonic uplift in northern Sibumasu terrane. [ABSTRACT FROM AUTHOR]

The so‐called Big Five mass extinctions of the Phanerozoic include two prominent Palaeozoic episodes: the end‐Ordovician and end‐Permian events, both with large biodiversity loss. We consider that the end‐Ordovician (Hirnantian) extinction could be best compared to the Middle Permian end‐Guadalupian (=Capitanian) extinction, rather than to the end‐Permian (Permo‐Triassic boundary; PTB) extinction. The end‐Guadalupian extinction, ca. 8 Myr before the PTB extinction, occurred as an independent episode under extremely unique global setting with the lowest sea level and lowest Sr isotopic ratios in seawater of the Phanerozoic. Multiple similarities exist between the end‐Ordovician (Hirnantian) and the end‐Guadalupian (Capitanian) events, such as the preferential elimination of sessile biota in the tropics, a global sea‐level drop and secular changes in seawater C and Sr isotope ratios, occurring under global cooling. The limited development of land vegetation suggests that the Ordovician extinction was restricted solely to the marine realm, with no prominent damages on land, and no large igneous province (LIP) recognized in the Ordovician. The comparison indicates that the two extinctions of the Hirnantian and of the Capitanian have been essentially triggered by similar causes/processes; nonetheless, biotic responses were different, owing to the more oxygenated status of surface environments in the Permian after the mid‐Palaeozoic terrestrialization. [ABSTRACT FROM AUTHOR]

The Fezouata Lagerstätte, discovered in the Lower Ordovician rocks of Morocco, is a Konservat‐Lagerstätte of prime scientific importance. It provides access not only to the ‘shelly’ (skeletonized) part of its fossil assemblages, but also to non‐biomineralized to lightly sclerotized organisms and to exceptionally preserved soft tissues of a complex ecosystem, mixing elements of both the ‘Cambrian Explosion’ and the ‘Great Ordovician Biodiversification Event’ (GOBE). The Fezouata Lagerstätte occurs at different intervals in the Fezouata Shale, a formation ranging from the lower Tremadocian to the upper Floian (Lower Ordovician). In spite of recent major advances in the detailed biostratigraphy of the Fezouata Shale, there is currently no consensus on the precise age of the fossiliferous levels yielding exceptionally preserved assemblages. Consequently, all available biostratigraphical evidence based on several fossil groups is here critically reviewed and discussed. It can be concluded that exceptional preservation is restricted to a few thin, discontinuous, lens‐shaped horizons occurring in two distinct parts of the Fezouata Shale: a lower interval (260–330 m above the base of the formation) and an upper interval (570–620 m). Integrated biostratigraphical studies, essentially based on investigations of graptolites, acritarchs and conodonts, indicate that the lower interval can be correlated with the upper Tremadocian, whereas the upper interval corresponds to the middle Floian. [ABSTRACT FROM AUTHOR]

This study presents a Cambrian–Ordovician (Cambrian, ‘Series 3’ – Katian, Ka4) brachiopod α‐diversity curve for the Iberian terrane. Three diversity pulses characterized the northern Gondwanan margin through the studied interval; an initial increase in linguliformean diversity that culminated during the Tremadocian (Tr3); a second, Darriwilian (Dw2) pulse caused primarily by a rise in orthid species; and a third pulse during Katian times (Ka3–4) marking the most diverse and phylogenetically complex faunas recorded in this study. Each of the three diversity pulses is phylogenetically distinct and characterized by large turnover rates. The first pulse consists almost exclusively of remnants of the Cambrian Evolutionary Fauna, whereas the second pulse shows a sudden rise of clades typical of the Paleozoic Evolutionary Fauna. The fact that otherwise typical Cambrian clades also radiated at the dawn of the Ordovician suggests that whatever facilitated the emerging Ordovician Radiation, also benefitted these ancient lineages. However, eventually the succeeding Paleozoic Evolutionary Fauna came to dominate during the second diversity pulse. This pulse represents a high‐latitude correlative to the main pulse of the Ordovician Radiation. Although it coincides with a globally occurring transgression of eustatic nature, our analysis shows that the generic composition remained overwhelmingly endemic up through the Darriwilian–Sandbian interval. Opposed to this, the third pulse coincides with the globally occurring Boda warming event, which also marks a time of global dispersal. In Iberia, this is reflected by almost entirely cosmopolitan brachiopod faunas, suggesting that the phases of rapid speciation which characterize the Ordovician Radiation had ceased by the mid‐Katian. [ABSTRACT FROM AUTHOR]

Chitinozoans are a key group in Ordovician and Silurian biostratigraphy, and the Baltic region hosts some of the largest collections of these microfossils in the world. Here, we present an online database – ‘CHITDB’ – for documenting and analysing the distribution of chitinozoans in the Baltic region. The system is integrated with the Estonian geocollections database and includes a public query portal (< http://chitinozoa.net>), which allows browsing and searching for chitinozoan taxa, samples, sections, references and SEM images, downloading raw data by sections, and generating range charts, summary reports and CONOP9 input files. The chitinozoan database holds currently over 35000 occurrence records of 300 chitinozoan taxa from 6400 micro‐palaeontological samples and 100 sections. Quantitative stratigraphical analysis of this data set enabled compilation of the highest resolution chitinozoan diversity curves through the Ordovician and Silurian to date, and assessment of the rates of evolutionary changes. The new model incorporates K‐bentonite and carbon isotope data that help to constrain time relationships between bioevents and environmental changes. The highest chitinozoan diversity in the Baltic region is encountered in late Darriwilian to mid‐Katian and in the Telychian, when the standing diversity reached 30–35 species. Overall, the latest Ordovician and Silurian faunas show more dynamic diversity patterns, with higher extinction and origination rates, than was typical for most of the Ordovician Period. [ABSTRACT FROM AUTHOR]

First Appearance Datums (FADs) of selected, easily recognizable acritarch morphotypes are assessed to determine their potential contribution to correlation between Lower and Middle Ordovician stages and substage divisions along the Gondwanan margin (Perigondwana) and between Perigondwana and other palaeocontinents. The FADs for 19 genera, species and species groups are recorded throughout their biogeographical ranges. The taxa investigated fall into three groups. Some have FADs at about the same level throughout their biogeographical ranges and are useful for long‐distance and intercontinental correlation. Among these are Coryphidium, Dactylofusa velifera, Peteinosphaeridium and Rhopaliophora in the upper Tremadocian Stage; Arbusculidium filamentosum, Aureotesta clathrata simplex and Coryphidium bohemicum in the lower–middle Floian Stage; Dicrodiacrodium in the upper Floian Stage; Frankea in the Dapingian–lower Darriwilian stages; and Orthosphaeridium spp., with FADs in the Dapingian–lower Darriwilian stages of Perigondwanan regions and at about the same level in Baltica. Other taxa, however, have diachronous (or apparently diachronous) FADs, and this needs to be taken into account when using them for correlation. A second group of genera and species, comprising Striatotheca, the Veryhachium lairdii group and the V. trispinosum group, have a recurring pattern of FADs in the Tremadocian Stage on Avalonia and in South Gondwana and West Gondwana, but in the Floian Stage of South China and East Gondwana. The third group, consisting of Arkonia, Ampullula, Barakella, Dasydorus, Liliosphaeridium and Sacculidium, have FADs that are markedly diachronous throughout their biogeographical ranges, although the global FADs of Arkonia, Ampullula, Liliosphaeridium and Sacculidium are apparently in South China and/or East Gondwana. It is possible that diachronous FADs are only apparent and an artefact of sampling. Nevertheless, an alternative interpretation, suggested by recurring patterns, is that some as yet undetermined factor controlled a slower biogeographical spread over time, resulting in diachroneity. [ABSTRACT FROM AUTHOR]

The Great Ordovician Biodiversification Event (GOBE) represents a diversification at lower taxonomic levels of most body plans that had appeared during the Cambrian explosion. Among trilobites, several novelties related to enrolment evolved during the GOBE. A kinematic analysis by means of 3D modelling of some new enrolment types shows no relationship with those of the Cambrian trilobites. While some structures emerged for the first time in Ordovician trilobites (e.g. articulations and panderian organs), other structures (e.g. anterior and posterior arch in head and tail) appear earlier in Cambrian trilobites. Our results suggest that the evolution of some groups was clearly rooted in the Cambrian explosion while others clearly appeared during the GOBE. [ABSTRACT FROM AUTHOR]

The Middle Ordovician (Darriwilian) Winneshiek Shale from Winneshiek County, Iowa, USA, hosts a Konservat‐Lagerstätte that has yielded a diverse fauna including soft‐bodied fossils. The shale is rich in organic content; in particular, algal material and fragmentary cuticular remains. Palynological acid treatment alongside modified, low‐manipulation processing enables the extraction of these ‘small carbonaceous fossils’ (SCFs) from the matrix, allowing a more detailed view of their morphology. Together these methods have yielded exceptionally well‐preserved crustacean‐type setae and a population of distinctive microfossils which we identify as the feeding appendages of a small‐bodied arthropod. We present two hypotheses for their identity: as either pancrustacean mandibles, or euchelicerate coxae. Overall, the detailed topological similarities and implied functional equivalence to the coxae of xiphosurid chelicerates, in particular, outweigh the resemblance to certain branchiopodan and hexapodan mandibles. In turn, however, the restricted size range and lack of associated limb or carapace fragments pose a taphonomic conundrum, suggesting an extreme biostratinomic bias. By comparison with previously described arthropodan SCFs from the Cambrian of Canada, the Winneshiek fossils extend the geographic, palaeoenvironmental and temporal range of this taphonomic window and provide a complementary tool for reconstructing the diversity and ecology of the Winneshiek biota. [ABSTRACT FROM AUTHOR]

Components of biodiversity are strongly scale dependent, but the relative importance of the patterns that operate at different scales and the links between them have been overlooked. To disentangle the ecological structure of Cambro-Ordovician trilobite assemblages from the Argentine Cordillera Oriental at different scales, we explore patterns of abundance, dominance and occupancy across the onshore-offshore profile, and through three time intervals: Furongian, earliest Late Tremadocian (Tr2), latest Middle Floian-earliest Late Floian (Fl2-Fl3). At the regional scale, single taxa are overwhelming dominant in the Furongian ( Parabolina) and in the earliest Late Tremadocian ( Leptoplastides). Several dominants occur in the Floian, but just one ( Famatinolithus) attains high occupancy and, rarely, high dominance. In contrast, only the Furongian records highly dominated local assemblages, whereas dominance distinctly decreases among Tr2 and Fl2-Fl3 ones. Thus, when both scales of analysis are combined, an unexpected scenario becomes evident: Tr2 assemblages resemble those of the Furongian at the regional scale, but mirror those of the Floian at the local scale. These results highlight a decoupling in local versus regional structures triggered by an earlier switch in dominance in local communities and a delayed change at the regional scale. Interestingly, this decrease in local dominance matches previous analyses accounting for a coeval step-up in local evenness, suggesting that the Tr2 appears as a pivotal interval in the reorganization of communities in the Cordillera Oriental. This scenario emphasizes that biogeographical regions witnessed different regional-scale processes, and suggests that scaling local and regional patterns provides new insights to unravel the history of biodiversity among benthic communities. [ABSTRACT FROM AUTHOR]

A carbonate ramp in the shallow-marine northwestern part of the Central Tarim Uplift, Bachu, NW China, exhibits an extraordinary Late Ordovician reef complex along the Lianglitag Mountains, exposed for a distance of about 25 km. Seven localities within the 'Middle Red Limestone' of the Upper Member of the Lianglitag Formation (Katian, Late Ordovician) illustrated the changes in biofacies and lithofacies: northern, seaward-directed patch reefs are replaced towards the south by coeval grain banks. The patch reef units are dominated by microbial and calcareous algal components. The reefs at the northernmost locality are knoll-shaped, kalyptra-shaped or irregularly shaped with sizes of individual reefs increasing from about 2 m in height and diameter. Stratigraphically upward, reefs notably expand to larger structures by several mounds coalescing; they are generally about 10 m thick and tens of metres in lateral extent. The maximum thickness of the main patch reef is more than 30 m, and its diameter is around 100 m. The reefal units turn into biostromes with gentler relief southward and still further south grade into banks composed of peloids and coated grains. The southernmost locality is still a shallow-water bank, and the coastline is not documented in the study area. The present evidence indicates that the Late Ordovician palaeo-oceanography provided a number of environments for the optimal growth of carbonate build-ups; microbial-calcareous algal communities could thrive in areas where the innovative metazoan reef frameworks consisting of corals and stromatoporoids did not play a significant role. The ramp morphology, especially changes in water depth, controlled the configuration of the reef complex. [ABSTRACT FROM AUTHOR]

The Tremadocian‐to‐Floian siliciclastic deposits of the Shirgesht Formation in the Kalmard Block of central Iran show abundant occurrences of the mid‐tier Trichophycus venosus, a common ichnotaxon in the archetypical Cruziana ichnofacies. This trace fossil records a considerable increase in exploitation of offshore infaunal ecospace in comparison with older formations. Here, Trichophycus is relatively long and wide, with numerous and deep successively stacked causative burrows, which form dense burrow systems building the Crowded Trichophycus ichnofabric (CTI). Such development of CTI and the increase in depth of bioturbation had a negative effect on preservation of shallow‐tier traces, for example arthropod burrows and trackways. This resulted in decreasing abundance of trilobite‐produced trace fossils towards the top of the succession. The palaeobiological and palaeoecological interpretation of CTI points to stable habitats in muddy substrates above the storm wave base with high content of food and oxygen in pore waters, low‐energy hydrodynamic regimes and a long colonization window. Moreover, the architecture and the morphological features of Trichophycus suggest a combined dwelling‐feeding activity of the resident fair‐weather producer showing the K‐selected/climax strategy. The ethology of the producer, palaeoecological interpretations and taphonomic signatures revealed that it preferred dewatered, compacted muddy substrates (firmgrounds) in offshore settings, which might be related to minor hiatuses or short‐lived discontinuities. Although the appearance of Trichophycus is concomitant to the earliest Cambrian agronomic revolution, it was uncommon until the early Ordovician, when locally it records infaunalization related to the Great Ordovician Biodiversification Event. [ABSTRACT FROM AUTHOR]

The continuous Upper Ashgill–Sheinwoodian carbonate succession in the most eastern Kozhym River area in the Subpolar Urals comprises the Yaptikshor (Rawtheyan), Kamennaya baba (Hirnantian), Ruchej and Manyuku (Llandovery–?Sheinwoodian) formations. The facies of the deep subtidal Yaptikshor Fm. mark an abrupt sea-level rise following emergence of the Bad’ya reef (Rawtheyan). Carbonate breccias at the base of the Kamennaya baba Fm. correlate with the beginning of the Hirnantian glaciation and change upwards towards the Ordovician–Silurian boundary with the development of light-grey massive boundstone/packstone shoal deposits. An abrupt change in facies to the Rhuddanian–Aeronian Ruchej Fm. continental slope environment marked the start of a long-term sea-level rise. The uppermost Aeronian–?Sheinwoodian is represented by submarine canyon carbonate conglobreccias of the Manyuku Fm. unconformably underlying the Balban’yu reef. The rapid facies changes at the base of the Hirnantian and at the Ordovician–Silurian boundary were of global eustatic origin. In contrast, the abrupt changes in the Rawtheyan and the formation of the Manyuku Fm. conglobreccias were of local or regional origin associated with tectonics. They were followed by the start of a regional transgression (Yaptikshor Fm.) and a global transgression marked by the initiation of the Balban’yu Reef in the Sheinwoodian. [ABSTRACT FROM AUTHOR]

Studies of ecosystem level changes in the geological record have found that the major extinction events eliminated many incumbent clades that had been ecologically dominant for long intervals. Surviving clades that had not been able to compete with the extinct incumbents were then able to evolve adaptations that allowed them to move into the niches vacated by the incumbents. Underlying this pattern is the inability of clades that do not occupy a particular niche to evolve adaptations that would permit them to compete with incumbent clades that are already successfully occupying that niche. The zoogeographic distributions of brachiopods in the Late Ordovician of Laurentia may also have been maintained by incumbency, which was disrupted by the end-Ordovician extinction event. Following the extinction event, an Early Silurian zoogeographic reorganization occurred, during which surviving clades evolved into the vacated epeiric sea niches in the Early Silurian. Just as incumbency plays a role in long-term evolutionary patterns, zoogeographic realms and provinces are also partially maintained by incumbency. [ABSTRACT FROM AUTHOR]

During the Middle Ordovician cephalopods became an important part of the macrofauna of the Baltoscandian carbonate platform. The earliest cephalopod abundance peak was reached during the early Darriwilian, within the Kunda Stage Yangtzeplacognathus crassus and Lenodus pseudoplanus conodont zones. In sediments of this time interval large orthoconic cephalopods often occur in masses with more than one specimen per square-meter on bedding surfaces. The assemblages are characterized by the strong dominance of often large endocerids. In proximal depositional settings coiled tarphycerids and other cephalopod groups are an important additional component. In the most distal settings orthocerids are the most important secondary component. Correspondence Analysis of assemblages throughout Baltoscandia revealed three distinct biofacies, which here are termed Orthocerid, Proterovaginoceras and Anthoceras Biofacies, respectively. The biofacies reflect differences in depth and proximity to the shoreline and are consistent with the Baltoscandian Confacies Belts. Spatial changes in absolute abundance and taxonomic composition indicate increased original cephalopod population densities and habitat expansion within the Y. crassus and L. pseudoplanus conodont zones. A nearly coeval abundance peak in a similar facies in South China indicates supraregional causes of the mass occurrence, probably reflecting a globally increased nutrient availability in the water column during the Darriwilian. [ABSTRACT FROM AUTHOR]

The late Ordovician Soom Shale Lagerstätte of South Africa has yielded Myodoprimigenia fistuca n. gen. and n. sp., the earliest and only known Ordovician occurrence of myodocopes, one of the major groups of ostracodes. M. fistuca is a likely sister group of the Upper Silurian 'cypridinid' myodocopes and allied forms. It had a thin, lightly mineralized and flexible shell with microstructures resulting from in vivo calcification processes. It probably fed on cephalopod carrion, thus extending evidence for a carnivorous scavenging lifestyle in ostracodes back by 200 Ma. The species was probably nektobenthic and thus consistent with the notion that the origin of the late Silurian pelagic myodocopes - and therefore of pelagic ostracodes - is to be charted in a benthic to pelagic ecological shift in the group. [ABSTRACT FROM AUTHOR]

The diachronous temporal and spatial distribution of the Hirnantia brachiopod fauna and the complicated pattern of terminal Ordovician events are documented through biostratigraphical analysis of the Ordovician-Silurian boundary strata in S China, Sibumasu, Xizang and elsewhere. The duration of these events (longer than the half Myr derived from isotopic excursions) indicates that they were not abrupt and instantaneous. The presence of some core taxa of the Hirnantia fauna in the upper P. pacificus Biozone (known from their earliest occurrence in China) signals the start of increased water ventilation due to the invasion of cool water across the Yangtze Basin. Low- and higher-diversity Hirnantia faunas related to onshore, shallow-water and to offshore, deeper-water environments, respectively, developed first in the basal and upper N. extraordinarius–N. ojsuensis Biozone. Disappearance of most of the fauna in the early N. persculptus Biozone suggests that the glacial maximum started to decline. The presence of the Hirnantia fauna in the upper N. persculptus to the lower P. acuminatus biozones indicates the continuation of cool water environments in some places. The diachronous disappearance of deteriorating environments (earlier in later Hirnantian and finally in the early Rhuddanian) is associated with geographical heterogeneity. Occurrences of atrypids, pentamerids and spiriferids along with key elements of the Hirnantia fauna in N Guizhou provide a link between the Late Ordovician radiation and Early Silurian recovery of these major brachiopod groups. [ABSTRACT FROM AUTHOR]

It was recently discovered that the stems of extant crinoids may survive after detachment of the crown, presumably feeding by the absorption of nutrients through the ectoderm. Previously, only one analogous, albeit morphologically dissimilar, pattern of crownless survival has been recognized from the fossil record. Certain Upper Ordovician (Cincinnatian) crinoid pluricolumnals from Kentucky, Ohio and Indiana, derived from the disparids Cincinnaticrinus spp., have rounded terminations reminiscent of some modern bourgueticrinid overgrowths. Such specimens have hitherto been interpreted as distal terminations of mature individuals that have become detached from their attachment structures and taken to an eleutherozoic existence. However, it is considered more probable that they represent overgrowths of the column following predatory decapitation. If this new interpretation is correct, then post-decapitation survival of crinoid stems is now recognized for most of the history of the crinoids, 'lethal' predation on crinoid crowns occurred at least as early as the Late Ordovician and ancient crinoid populations can no longer be determined merely by counting crowns. [ABSTRACT FROM AUTHOR]

Extensive work during the last decade has led to the recent decision by the International Subcommission on Ordovician Stratigraphy that the base of the Middle Ordovician Series should be placed at the base of the Baltoniodus triangularis Conodont Biozone in the Huanghuachang GSSP (Global Stratotype Section and Point) section near Yichang, Hubei Province, China. A review of the biostratigraphy of successions in many parts of China shows that for various reasons, it is currently difficult to recognize the precise boundary level in many regions, and additional studies are clearly needed. A newly exposed, previously poorly known, condensed section in deeperwater facies at Hengtang near Jiangshan in the Chiangnan (Jiangnan) belt has yielded a substantial number of important graptolites and conodonts through the boundary interval. It provides a more informative illustration of the relations between the ranges of several key taxa of these groups than any other section in China, and the level of the base of the Middle Ordovician appears to be within an about 1.8 m thick interval of Ningkuo Formation, and lies in the lower Isograptus caduceus imitatus Biozone. [ABSTRACT FROM AUTHOR]

The Ellis Bay Formation on Anticosti Island has long been recognized for the biostratigraphic importance of its latest Ordovician conodont, palynomorph, and shelly fossil assemblages. However, a sparse record of graptolites has made it difficult to correlate these assemblages with the graptolite biozonation. Restudy of some previously described and examination of newly collected normalograptid specimens from the Ellis Bay and lower Becscie formations, however, shows that biostratigraphically important taxa are present and these species provide important constraints on the age of the strata. Normalograptus parvulus and N. minor have been identified in the upper half of the Ellis Bay Formation, suggesting that these strata are late Hirnantian in age ( N. persculptus Biozone). Normalograptus imperfectus and Normalograptus sp. aff. N. acceptus occur in the basal beds of the Becscie Formation, indicating that these strata are earliest Silurian. These graptolite data support the hypothesis that the positive carbon isotope excursion seen in the uppermost strata of the Ellis Bay Formation is isochronous with that seen in the Hirnantian strata at Dob's Linn, Scotland, and does not span much of the lower to mid-Hirnantian, as is the case in Arctic Canada and Nevada, USA. Anticosti Island, Hirnantian, graptolites, Ordovician, Silurian. [ABSTRACT FROM AUTHOR]

The Agronomic Revolution implies a gradual sophistication of organism-substrate interactions and progressive colonization of shelf environments by vagile endobenthos in the late Ediacaran and Cambrian periods. These changes are impressively mirrored in a palaeontological record of ichnoassemblages in marine siliciclastic facies. In contrast, endobenthic communities in carbonate successions remained comparatively poor until a fundamental transformation during the Great Ordovician Biodiversification Event. Herein we report complex open burrows (Thalassinoides and Olenichnus) from the Sukharikha Formation exposed near the Plakhinskii Island (Yenisei River, Igarka Uplift). Lithological and chemostratigraphical correlation with the stratotype suggest the Terreneuvian age of the fossil-bearing strata accumulated in storm-agitated mid- to distal inner-ramp settings. Each of the ichnotaxa occurs in a specific deposit in the studied section: Olenichnus is localised exclusively in the background-sedimentation deposits, whereas Thalassinoides occurs in the storm-event beds. Our data support early reports suggesting that colonization of marine carbonate sediments by burrowing metazoans was initiated already in the Terreneuvian and became a solid basis for the following development of deep-tier bioturbation in carbonates in the Ordovician Period. [ABSTRACT FROM AUTHOR]

Benedetto, J.L. 2013: Presence of punctae in the 'plectorthoidean' brachiopod Famatinorthis turneri (Middle Ordovician) from western Argentina: implications for early diversification of punctate orthides. Lethaia, Vol. 46, pp. 170-179. Famatinorthis Levy & Nullo is a distinctive orthide brachiopod of Dapingian age from the volcaniclastic rocks of the Famatina Range of western Argentina. Although it was originally classified among the plectorthoideans, a new collection from the La Escondida Formation has yielded exceptionally well-preserved moulds of Famatinorthis turneri in which silicified infillings of punctae are clearly visible, leading to the reassignment of the genus to the dalmanellidines. In this paper, phylogenetic analyses are used to determine the evolutionary relationships of Famatinorthis, the Tremadocian linoporellid Lipanorthis, and other Ordovician Gondwanan genera. The placement of Plectorthoidea in the same major clade as linoporellids, and the separation of Dalmanellidina as an independent clade are the most important features of all shortest trees, supporting the idea that linoporellids may have originated from a plectorthoid ancestor. Cladistic analysis reveals that Lipanorthis lies close to the ancestry of the linoporellid lineage, and Famatinorthis clusters within the more derived taxa of the clade with which it shares a large septalium. It seems that the presence of endopunctae in the orthides does not necessarily indicate close phylogenetic relationships as it could have occurred at different times in different clades. If the homoplasic nature of endopunctae in the order Orthida is supported by further morphologic and phylogenetic studies, the fundamental division of orthides in non-punctate (Orthidina) and punctate (Dalmanellidina) may need revision. □ Brachiopods, Ordovician, Gondwana, Famatina, phylogeny, punctate orthides. [ABSTRACT FROM AUTHOR]

Multivariate analysis based on nine biometric characters of 171 Late Ordovician rhynchonellide specimens from nine upper Sandbian-upper Katian localities in North America supports the hypothesis that one of the diagnostic taxa of the North American epicontinental brachiopod fauna, Hiscobeccus, evolved from Rhynchotrema, which lived predominantly in peri-cratonic settings. The oldest known Hiscobeccus, H. mackenziensis of early Katian age, exhibits transitional characteristics between Rhynchotrema and Hiscobeccus, and it clusters more closely with Rhynchotrema than with younger species of Hiscobeccus of mid-late Katian (Maysvillian-Richmondian) age. Diversification of the Hiscobeccus lineage in epicontinental seas was characterized by drastic increase in shell size, globosity and lamellosity, especially in palaeoequatorially located inland basins. Such morphological trends are interpreted as adaptation to relatively shallow, muddy substrates, moderate water turbulence, relatively low oxygen content and unstable supply of nutrients in generally overheated epicontinental seas with sluggish circulation. [ABSTRACT FROM AUTHOR]

Review of the traditional separation of global Ordovician conodont distribution into the North American Midcontinent Province (NAMP) and North Atlantic Province (NAP) reveals a confusing variety of concepts and definitions that hinder biogeographic analysis. Use of this twofold scheme and its subsequent variants should be­discontinued in favour of the more detailed divisions proposed here. Major biogeographical entities of the Shallow-Sea and Open-Sea Realms, separated by the shelf-slope break, are both further subdivisible into Tropical, Temperate and Cold Domains. In the Cold domains, faunal differences between the two Realms and their subdivisions are not easily discernible, since biofacies zones and different habitats were highly condensed. Faunal differences are amplified in the tropical regions, where the North American Midcontinent Province and North Atlantic Province were originally defined. Recognition of endemic taxa is essential for finer classification within domains of the Shallow-Sea Realm (SSR). Our preliminary analysis of Early Ordovician conodont distribution identifies the Laurentian Province (in the Tropical Domain), Australian­(Tropical Domain), North China (Tropical Domain), South China (Temperate Domain), Argentine Precordillera (Temperate Domain) and Balto-Scandian Province (in the Cold Domain). The Open-Sea Realm (OSR) is dominated by cosmopolitan and widespread taxa, and formal subdivision at provincial level is yet to be achieved. The North Atlantic Province encompasses both the Open-Sea Realm and the Temperate and Cold Domains of the Shallow-Sea Realm. The North American Midcontinent Province sensu stricto is more or less equivalent to the Laurentian Province, representing shallow-water regions fringing Laurentia; in a broader sense the North American Midcontinent Province includes all provinces of the Tropical Domain within the Shallow-Sea Realm. [ABSTRACT FROM AUTHOR]

Some of the world's oldest macroborings occur in hardgrounds in lower Ordovician (Arenig) limestones exposed on the island of Öland, southern Sweden. The trace fossils, which are described here as Gastrochaenolites oelandicus isp. nov., appear to be dwelling structures excavated in the indurated substrate by invertebrates of unknown taxonomic affinity. They are the oldest examples of this ichnogenus. The appearance of a macroboring life habit at this early time represents a revolutionary new adaptive strategy for inhabiting carbonate hardgrounds. However, this innovative strategy apparently was not successful for the long term, because this particular macroboring taxon seems to have disappeared shortly after its early Ordovician appearance. [ABSTRACT FROM AUTHOR]

Adachi, N., Ezaki, Y. & Liu, J. 2011: The oldest bryozoan reefs: a unique Early Ordovician skeletal framework construction. Lethaia, Vol. 45, pp. 14-23. The oldest bryozoan reefs occur in the Lower Ordovician (late Tremadocian) Fenhsiang Formation of the Three Gorges area, South China. These reefs show a unique type of bryozoan ( Nekhorosheviella) framework, and were constructed as follows: the first stage involved colonization by lithistid sponges, which acted as a baffler to trap sediments, providing bryozoans with a stable substrate for attachment. The bryozoans then grew as an encruser on the surfaces of sponges, showing a preferential downwards and lateral growth within the sponge scaffolding to avoid biological and physical disturbance. Finally, these biotic combinations among skeletal organisms formed a rigid, three-dimensional skeletal framework. This mode of bryozoan growth in association with lithistid sponges is remarkable and unique in its growth direction, and the appearance of such reefs, just prior to the widespread development of skeletal-dominated reefs as part of the Great Ordovician Biodiversification Event, provides an excellent example of the earliest attempts by skeletal organisms to form frameworks by themselves. This find significantly enhances our understanding of the initial stages of skeletal-dominated reef evolution and the ensuing development of reefs during the Middle-Late Ordovician. □ Bryozoa, Early Ordovician, lithistid sponge, Ordovician radiation, reef. [ABSTRACT FROM AUTHOR]