We describe the pilekiine trilobite genus (Family Cheiruridae) Radiantospina gen. nov. (type species R. helioaspis sp. nov.) from the Lower Ordovician (upper Tremadocian, Sagenograptus murrayi graptolite Zone) Fezouata Shale in Morocco. Radiantospina is characterized by a distinctive thoracic morphology in which the proximal part of the thoracic pleura bears a transverse pleural furrow that extends two-thirds of the total width of the pleural band. Radiantospina resembles the poorly known genus Courtessolium from the Tremadocian (Euloma filacovi Zone) of the southern Montagne Noire, France, but differ in terms of the thoracic pleural furrow morphology and the shape and arrangement of the pleural spines. We also revise the species Foulonia peregrina, the type species of the genus. Foulonia is the stratigraphically oldest genus assigned to the cheirurid subfamily Eccoptochilinae. New material from the Floian levels (?Baltograptus jacksoni graptolite Zone) of the Fezouata Shale shows the occurrence of the genus along the northwestern perigondwanan margin linking Montagne Noire (South France) and Morocco (NW Africa). center dot
Ordovician rocks east of the Prague Basin are very rarely exposed because they are largely concealed beneath the platform sediments of the Bohemian Cretaceous Basin. A unique record of Ordovician strata occurs at Pardubice-Semtin, where Palaeozoic xenoliths were brought to the surface by a nephelinitic basalt diatreme that pierced the Mesozoic cover. In 1896, Jaroslav Jilji Jahn briefly reported a fossil assemblage from these xenoliths, including machaeridians, hyolithids, brachiopods, molluscs, and trilobites, which closely resembles the fauna of the Late Ordovician Vinice and Zahorany formations of the Prague Basin. Most of Jahn's material was long considered lost but it was rediscovered in 2020. Its thorough revision, including the first study of associated acritarchs and chitinozoans, refines the age and stratigraphic affinity of the fauna. A continuous distribution of Ordovician rocks between the Prague Basin, the bedrock of the Bohemian Cretaceous Basin, and thezelezne hory Mountains area has been traditionally assumed. Differences in faunal composition, lithology, and metamorphism, along with detected and inferred tectonic faults, suggest a discontinuity between the Ordovician basement beneath the south-eastern part of the Bohemian Cretaceous Basin and the Ordovician of thezelezne hory Mountains area. Even though there are numerous similarities between fossils at Pardubice-Semtin and that of the Prague Basin, we consider them more likely to represent distinct, albeit likely communicating, basins within the Tepla-Barrandian Unit.
The family Naraoiidae represents Lower Paleozoic artiopodan euarthropods with non-biomineralized exoskeletons that are particularly abundant in Cambrian Konservat-Lagerstatten. Despite this early abundance, they are much rarer in post-Cambrian deposits. Soomaspis splendida Fortey & Theron, 1994, one of the few known Ordovician species, was described from the Hirnantian Soom Shale Member of the Cedarberg Formation, South Africa. This naraoiid is characterized by a circular, featureless cephalon, three thoracic tergites, and a pygidium with five pairs of interpleural furrows. Here we describe a new species of Soomaspis-Soomaspis labutai sp. nov.- from the Katian Kraluv Dvur Formation of the Prague Basin (Czech Republic), based on a single specimen recovered from the recent construction of a new metro line in Prague. Soomaspis labutai sp. nov. is distinguished from S. splendida by its proportionally shorter pygidium and different exoskeletal sculpture. The occurrence of Soomaspis in Bohemia demonstrates that this genus was present along the Gondwanan margin prior to the Hirnantian glaciation and survived both pulses of the end-Ordovician mass extinction. Soomaspis distribution in two geographically distant regions, coupled with its occurrence in high-latitude settings, indicates a broader paleogeographic and ecological distribution than previously recognized. The new species also demonstrates that naraoiids were more widespread during the Ordovician than the current fossil record implies.
From the Cap de la Chevre Formation (Fm.) of the Crozon Peninsula (BegArGwin locality, Brittany, northwestern France) an exceptional trace fossil site is described and discussed. A mass occurrence of remarkably large sized trilobite trails of Cruziana furcifera d'Orbigny, 1842, is reported for the first time in France. An additional layer exposes Cruziana barriosi Baldwin, 1977, which represents the only trilobite trace of this second assemblage, and occurs in large numbers. Cruziana barriosi is first reported from Europe outside Iberia. The Cruziana furcifera and Cruziana barriosi trace fossil assemblages from BegArGwin, which both represent the Cruziana rugosa group, show very low ichnodiversity (n = 2-3). The ichnocoenoses and the sedimentological characteristics of the host rock suggest an ecologically unstable, transitional marginal marine depositional system exposed to elevated ecological stress. Palaeogeographically situated in high southern latitudes, the assemblages and deposits show close relations to similar Gondwanan occurrences, as on the Iberian Peninsula and in the Middle East. The Cruziana rugosa group, in particular, is confirmed as a valuable tool for stratigraphic correlation, as well as for refining palaeoecological-palaeogeographic reconstruction models for this part of Gondwana. The stratigraphic position of the Cap de la Chevre Fm. is evaluated. Based on the BegArGwin trace fossil assemblages, a depositional age of early to middle Floian (Early Ordovician) is most likely, at least for the fossil-bearing upper part of the Cap de la Chevre Fm.
The Lower Ordovician (Tremadocian) linguliformean brachiopods of the southeastern part of the Anglo-Brabant Massif are documented systematically for the first time. The material belongs to a single Belgian locality (La Roche-en-Brabant), situated in one of the few valleys that incise the Mesozoic-Cenozoic cover, and more precisely from the topmost part of the siliciclastic Mousty Formation (Tangissart Member). Here, minute, poorly diverse linguliformeans are associated with planktic graptolites (Rhabdinopora) and nileid trilobites (Platypeltoides). They consist of three species belonging to three genera (Obolidae and Elkaniidae), of which only Broeggeria is known with certainty, due to the poor preservation of the material. In the Belgian part of the Stavelot-Venn Inlier, the presence of linguliformean brachiopods within the Floian Les Plattes Member of the Ottre Formation, which were reported more than 150 years ago, remains unconfirmed. The genus Broeggeria, known from several Belgian Tremadocian localities, is a relic from the Cambrian brachiopod fauna. By the Tremadocian it is well established globally between the Low-Latitude and High-Latitude provinces. The Belgian assemblage has strong similarities with assemblages from Baltica reflecting the early Palaeozoic changing palaeogeography. center dot Key words: Brachiopoda, Linguliformea, Tremadocian, Floian, Avalonia.
This study describes a Katian acritarch assemblage from the Wanhe section, northeastern Yunnan, South China, and discusses its biostratigraphic, paleogeographic, and paleoenvironmental implications. Thirty-eight samples were collected from the Zhenxiong, Lianfeng, Daduhe, and Lungmachi formations, with 11 yielding acritarchs from the upper Lianfeng and lower Daduhe formations. A total of 26 species assigned to 20 genera were identified, including 12 species in open nomenclature. Biostratigraphically, the assemblage is constrained to the late Katian (Ka4) based on co-occurring graptolitebiozones (Dicellograptus complanatus,D. complexus) andzirconU-Pb dates (444.65-442.99 Ma) from K-bentonites. Key taxa such as Baltisphaeridium aspersilumiferum, and Cheuletochroa homoia confirm a Late Ordovician age, with some taxa (e.g., Oppilatala sp.) suggesting Silurian affinities. Paleogeographically, the assemblage exhibits mixed affinities with Laurentian/Baltican (e.g., Baltisphaeridium, Hoegklintia) and Gondwanan/ peri-Gondwanan (low diversity, limited Navifusa) assemblages, supporting close links between South China, North China, and Tarim during the Katian. In terms of paleoenvironment, the assemblage reflects a deep-water setting (BA4-BA5) with a shallowing trend from the Daduhe Formation to the Kuanyinchiao Bed. A late Katian transgression followed by a latest Katian-Hirnantian sea-level drop may have influenced acritarch distribution. The dominance of Evittia remota, a cosmopolitan taxon, aligns with the "equatorial cold-water tongue" model, linking its occurrence to Late Ordovician climate fluctuations.
Bromalites, the fossilized remains of material sourced from the digestive system of organisms, are often overlooked in micropaleontological samples, but offer valuable insights into the paleoecology of ancient ecosystems. This study focuses on Furongian (upper Cambrian) to Floian (Lower Ordovician) bromalites from the Central Andean Basin of the Eastern Cordillera, NW Argentina. In many samples, bromalites dominate as the primary organic residue after acid treatment. The recovered assemblage consists of 276 coprolites and cololites, including Anfractuosocoprolithus aphelus and three unidentified ichnospecies (A, B, and C). Furthermore, a new ichnogenus, Helicobromites, is established, with the description of a new ichnospecies, H. andinus. These ichnospecies may reflect the activity of mollusks as well as that of poorly documented organisms such as ascidian tunicates, polychaetes, holothurians, and perhaps nektonic vertebrates. In this way, the coprolites and cololites from the Eastern Cordillera significantly enhanced the reconstruction of lower Paleozoic ecosystems in the southwestern Gondwanan seas.
The mitrate Mitrocystella incipiens (Barrande, 1887) is a locally abundant stylophoran echinoderm, with a short stratigraphic range but a wide palaeobiogeographic distribution in the high-latitude peri-Gondwanan regions of the Mediterranean Province: Czech Republic (Prague Basin, Bohemia), France (Armorican Massif, Brittany), northern Portugal and Spain (Iberian Massif). Two regional subspecies were previously identified based on the morphology of their thecal outlines: M. incipiens incipiens (Barrande, 1887) (Prague Basin), and M. incipiens miloni Chauvel, 1937 (Armorican Massif and Iberian Peninsula). A sample of 40 complete and well-preserved individuals from the Armorican Massif, the Iberian Peninsula, and the Prague Basin was selected to assess whether these morphotypes could be distinguished through quantitative analysis. Geometric morphometric analysis of their theca confirmed the existence of morphological differences between the Armorican and Czech populations, but also identified that the Iberian specimens are morphologically intermediate between those from the Armorican Massif and Prague Basin. Furthermore, the antero-lateral margins of the Iberian specimens present a delicate pustulose ornamentation, while the lower thecal surface of the Armorican and Czech individuals is completely smooth. The Iberian specimens are thus assigned to a new subspecies: M. incipiens pustulosa ssp. nov. These results support the idea that all populations of Mitrocystella belong to the same species, M. incipiens, which is characterized by a broad phenotypic variation. Together with geographic isolation, subtle environmental differences between the three regions (e.g. depth) may have contributed to shape these ecophenotypes. Finally, the first example of abnormal thecal plating in Mitrocystella incipiens is described in a specimen from Spain and its possible phylogenetic implications are discussed.
Marine carbonate oolites are a key feature of the Hirnantian Stage (445.2-443.8 Ma) and their formation may be the combined result of latest Ordovician glacial eustasy and the associated mass extinction event. In this paper, we provide the first highly time-resolved carbon isotope data (delta C-13(carb)) from the Keel Oolite in the Arbuckle Mountains of southern Oklahoma, aiming to clarify its temporal relationship with the overall Hirnantian Isotope Carbon Excursion (HICE) and refine the chronostratigraphy of the oolites in the southwestern United States. However, analyses of the Keel Oolite at the type locality in Holnam quarry, at the classical Highway 77 road-cut, and in the Sunray DX-Davis 1-5 drill core, reveal only a fragmentary carbon isotope record, making any detailed chemostratigraphic correlation of the local Hirnantian difficult. The oolite yields overall consistent delta C-13 trend lines and weak to moderate co-variance (R-2 ranging from 0.04-0.49) between carbon and oxygen, indicating no to moderate diagenetic alteration, still they display a ca. 1-2 parts per thousand offset of the baseline between localities. As there is no firm evidence for any steep increase or decrease in the delta C-13 values, it is suggested that the oolites correspond to the peak and plateau interval of the HICE. Brachiopods of the same strata belong in the Edgewood-Cathay Fauna, which normally appears in the time interval corresponding to the falling limb of HICE. At the Highway 77 road-cut, our carbon isotope stratigraphy reaches nine metres into the Silurian succession immediately overlying the oolite, corroborating previous interpretations of an extremely discontinuous stratigraphy with prominent unconformities. Based on the combined information from conodont faunas and our delta C-13(carb) data, however, we infer or identify the overall position for preserved parts of Silurian delta C-13 excursions in the section, including the Late Aeronian Carbon Isotope Excursion (LACIE), the Valgu Carbon Isotope Excursion (Valgu CIE), Early Sheinwoodian Carbon Isotope Excursion (ESCIE), the Mid Homerian Carbon Isotope Excursion (MHCIE), and the Mid Ludfordian Carbon Isotope Excursion (MLCIE). Our geochemical data thus reinforce a modest stratigraphic completeness of the Ordovician-Silurian boundary succession in the Arbuckle Mountains.
Soluta is a long-ranging, low-diversity class of Palaeozoic echinoderms with a particularly discontinuous fossil record. This study describes their second worldwide occurrence in the Silurian, and their earliest record after the Late Ordovician mass extinction. The new material from the Nantglyn Flags Formation (Wenlock Series) in Wales (UK) is herein assigned to Dehmicystis aff. ariasi, based on characteristic morphological features, such as a globose, rounded theca made of smooth, unomamented plates; a non-apical brachiole inserted on the lower thecal surface; and a large periproct located on the upper thecal side. This new occurrence extends the stratigraphic and palaeobiogeographic distribution of the genus Dehmicystis, previously known from the Ludlow of Spain, the early Emsian of Germany, and possibly the Pragian of Belgium. Dehmicystis aff. ariasi provides crucial data for deciphering the evolutionary patterns and recovery of solutans after the Hirnantian mass extinction. Their cryptic fossil record may result, at least partly, from their restriction to deep environments (outer shelf, slope), which are less frequently preserved than more proximal settings.
Extensive field-based sampling of the shallow water trilobite faunas of the northern Laurentian palaeo-margin (present day western North America) has yielded an abundance of well preserved, secondarily silicified, faunas spanning the Lower Ordovician. As sampling has accumulated, some very rare species have been revealed. It is unusual to encounter new post-Cambrian trilobites whose family-group affinity is obscure, but two new Stairsian (midTremadocian) genera contain reasonably well known species with effaced morphologies that have no obvious close comparisons among other Ordovician taxa. Smoothcanyonops gen. nov. (type species S. smoothcanyonensis sp. nov.) includes species with dorsally smooth, considerably effaced morphology, apparently with yoked librigenae. A second assigned species is S. middlensis sp. nov. Ceeops gen. nov. (type and only species C. housensis sp. nov.) is also mostly unsculptured and effaced, but has a greatly anteriorly expanded cranidium, broad librigenae, and very broad cephalic doublure. While their thin cuticles, general lack of sculpture, and weakly expressed dorsal furrows indicate they could be representatives of the same family-group taxon, there are also considerable morphological differences between them. Among other trilobites, they both have some resemblances, particularly in librigenal morphology, to bathyurids. However they are older than the oldest widely agreed species of bathyurids and they lack many bathyurid features. At present their affinity is difficult to assess with any confidence.
The palaeoecology of a volcanically influenced Silurian sea floor is analysed from the Smoking Quarry, Kozolupy, Czech Republic. Platy limestones with small coral-stromatoporoid reefs developed around the Svat & yacute; Jan volcanic centre in the Prague Basin, alternating with atrypid brachiopod-rich tuffitic shales. The reef building organisms are preserved in situ or very little disturbed, as are the brachiopod assemblages, indicating limited reworking. Extrinsic climatic factors and diagenesis are considered with regard to the sedimentary cyclicity. Limestone firmgrounds and hardgrounds indicate early shallow cementation and exposure of irregular, probably nodular beds enhanced by diagenetic segregation of carbonate. In the volcanic setting, limestones may represent periods of greater current activity, when volcaniclastic sediment was washed into deeper areas, while shales represent more quiescent periods. The Kozolupy section studied represents the uppermost Gorstian volcano-sedimentary facies of the Kopanina Formation going up into shallow water limestones in the early Ludfordian. The succession is compared in its regional context with other sections in the Amerika Anticline, illustrating the spatial development of biofacies along the axis of the Prague Basin and the effects of global eustatic oscillations.
A comparison of high-resolution stratigraphic records of Ludfordian global environmental changes with the stratigraphic distributions of brachiopods belonging to the genera Dayia and Shaleria are used to explain changes in benthic associations on the opposite sides of the Rheic Ocean. To elucidate these changes, we analysed data from several localities from Gotland (Laurussia) and the Prague Basin (peri-Gondwana). The current analysis revealed that Ludfordian Dayia navicula from the tropical region of Laurussia and Dayia minor from the temperate region of Gondwana represent two closely related but distinct species. Available data suggest that the Dayia navicula Association originated in the Avalonian part of Laurussia. After the decline of the Dayia navicula Association in the Anglo-Welsh Basin, the same association continued in the Baltic Basin of Laurussia. The initial environmental changes associated with the Siluricus Ocean Anoxic Event, which caused the Lau/Kozlowskii extinction events and preceded the Mid-Ludfordian Glaciation, triggered the migration of Dayia species over the Rheic Ocean. At the same time, this genus appeared in the Prague Basin, located in the periphery of Gondwana. The same migration way is also recorded for brachiopod genera Shaleria and Navispira. The subsequent environmental changes associated with the Mid-Ludfordian Glaciation, such as shallowing and cooling, had a negative impact on Dayia populations, but favoured the expansion of Shaleria populations. This replacement trend in benthic communities occurred on the opposite sides of the Rheic Ocean, on the Gotland and in the Prague Basin. Shaleria populations culminated during the late rising phase of the mid-Ludfordian carbon isotope excursion (MLCIE) and persisted through its steady phase, but then began to decline. Our results reveal that the occurrence and succession of brachiopod associations, as well as the biotic reaction of benthic invertebrates to global environmental changes on both sides of the Rheic Ocean, were similar and roughly synchronous. In the taxonomic section of the present paper, a minute species, Dayia minuscula sp. nov., restricted to the deglaciation period following the Mid-Ludfordian Glaciation, is described from the Prague Basin. center dot
The practice of formalizing chemostratigraphic units and defining isotopic zones based on excursions has become widespread. For more than three decades, stable carbon isotopes have played an important role in the solution of Silurian stratigraphy. delta C-13(carb) data supplement other stratigraphical proxies, allowing the subdivision of geological sections and more precise correlation. In this paper we provide new delta C-13(carb) data from the Silurian section of the Ledai-179 borehole, which is located in central Lithuania. The lower Silurian geological succession of Ledai-179 well is composed of carbonate and sulfate deposits. Two positive carbon isotope excursions were identified in the Ledai-179 borehole: Ireviken and Mulde. In this study, we employed stable carbon isotope data from Ledai-179 and Jocionys-299 (Eastern Lithuania) boreholes and the cross recurrence plot as additional tools to compare two time series (Telychian-Homerian interval) in a data-point-wise manner. The results indicate that stable carbon isotope data exhibit sufficient temporal and spatial coherence to serve as a reliable additional tool for correlating geological sequences.
The Parallelodontidae is one of six families within the arcoid Bivalvia that are considered to have a temporal range extending from the Ordovician to the Recent. Nevertheless, its origin and early diversification remain poorly understood, despite over 150 years of research. We reviewed the Devonian and pre Devonian taxa attributed to the Parallelodontidae with respect to parallelodontid morphology in the strict sense, particularly shell outline and hinge characteristics. Out of some fifty species, only a few match the typical parallelodontid morphology. Most of them can only vaguely be attributed to the Parallelodontidae, as poor preservation can obscure diagnostic features, causing potential confusion with coeval genera of the Heterodonta and Protobranchia with comparable external morphology. All Ordovician and Silurian taxa previously attributed to Parallelodon or presumed to possess parallelodontid characteristics turned out to be misclassified. Parallelodon mandelensis from the upper Emsian shallow marine Rhenotypic (Rhenish) Facies of Germany undoubtedly has a parallelodontid hinge and appears to be the earliest member of the family. In the Middle Devonian, primarily in the shelf region deposits of the Rheic Ocean in Central Europe and eastern North America, a first, minor radiation occurred. With the transition from the Devonian to the Carboniferous, a second, more pronounced radiation of parallelodontids led to significantly higher parallelodontid diversity.
The evolution of shell colouration in Palaeozoic cephalopods is still poorly understood. To date, thirtysix species of orthoceratoids have been described that display colour patterns on their shell. Thirteen species are newly added herein or re described from the Ludlow of Bohemia and two from the Mississippian of Belgium. The colour pattern is best documented in pseudorthoceratids. Some gaps in the fossil record still exist and seemingly separate periods dominated by specific types of shell colour patterns. Ordovician pseudorthoceratids have uniform, regular and evenly spaced longitudinal stripes. A similar but less regular type of colouration also occurs in Silurian pseudorthoceratids-rhythmised, irregular, interrupted and anastomosing colour stripes. After a gap in the Early Devonian, younger pseudorthoceratids possess a chevron pattern. A difference in the colour pattern in hatchlings and later growth stages is documented in the Carboniferous Pseudocyrtoceras. The restriction of colouration to the dorsal side of the shell in Devonian and Carboniferous pseudorthoceratids, which was previously interpreted as reflecting horizontal biological orientation of the shell and countershading, is questioned. The adaptive control and protective function of the shell colour patterns are indicated by the diversification of colour patterns in the Silurian, the emergence of the chevron pattern in the Devonian and early Carboniferous, the relationship between colour patterns and shell shape, the colour pattern polymorphism, and the ontogenetic changes in colouration. The pseudorthoceratid Pellucidoceras gen. nov. is established herein. Its type species, the Silurian P. decipiens, shows an intraspecific variability in the number, width, and spacing of stripes, and possibly represents case of colour pattern polymorphism. center dot Key words: Cephalopoda, Orthoceratida, shell colouration, palaeoecology, Silurian, new taxa.
