Conodont Diversity Research Articles

Bio-, Lithostratigraphic and Geochemical Markers of Global Events in the Upper Devonian of the South of Western Siberia and their Value for Inter-regional Correlations

Abstract —Upper Devonian carbonate reef complexes have been studied on the territory of the Kolyvan-Tom’ Folded Area in sections in the right bank of Tom’ River. Facies analysis of the exposed part of the reef complex indicates the predominance of fore-reef and continental margin depositional environments of a tectonically active margin. The identified conodont associations are represented by cosmopolitan representatives of the genera Ancyrodella, Ancyrolepis, Icriodus, Mehlina, Palmatolepis, Polygnathus and “Polylophodonta” suggesting a correlation with the punctata–jamieae, rhenana–linguiformis, triangularis and Lower crepida conodont zones. The largest conodont diversity occurs at the triangularis/crepida boundary. Biofacies analysis of ostracod distribution has led to identification of characteristic associations and their restriction to certain parts of the palaeobasin. Substage boundaries yielded ostracods with both smooth and ornamented shells. In the lower part of the substages, smooth forms predominate, whereas the middle and upper parts of the substages are characterised by forms with tuberculate and reticulated surface. Hollinella valentinae Beds were traced in the Upper Frasnian Solomino Formation, and Acratia granuliformis Beds were traced in the Lower Famennian Kosoy Utyos and lower Mitikha members. Isotope geochemistry of the Upper Devonian sections of the south of Western Siberia reveals Frasnian global events – the Middlesex/punctata and the Upper Kellwasser, their stratigraphic position confirmed by palaeontological data, as well as by the globally expressed negative carbon isotope anomaly. These boundaries are marked by changes in depositional regime reflecting sea-level eustatic fluctuations, which are complemented with faunal changes.

Ordovician conodont biodiversity analysis from the Precordillera (Argentina): a new insight in the global context of the GOBE

ABSTRACT The rapid diversification of conodonts during the Ordovician has been extensively studied by several authors, each presenting distinct diversity curves for different paleocontinents. This study analyzes trends in conodont biodiversity in the Precordillera region, spanning from the late Tremadocian to the early Sandbian ages. A conodont dataset, incorporating species previously identified in sections across Central and Eastern Precordillera, is utillized. This contribution presents the conodont diversity curve for the Lower to early Upper Ordovician in the Precordillera for the first time. The resulting conodont biodiversity pattern reveals that the initial peak of diversification occurs during the O. intermedius Zone (middle-late Floian). A sharp decline in biodiversity is observed during the Dapingian. Finally, during the early Darriwilian, there is a rise in the diversification of conodont species, reaching a peak in the L. pseudoplaunus Zone. This pattern is also compared to curves from Baltica, South China, North China, and Tarim, showing similar trends among them. The variation in Lower-Middle Ordovician conodont diversity in the Precordillera may be linked to different pulses or events within the ‘GOBE’ (Great Ordovician Biodiversification Event).

Biodiversity and evolutionary phases of Lochkovian (Lower Devonian) conodonts in the Pyrenees: A comparative study

This paper aims to evaluate the zone-by-zone changes in Lochkovian conodont biodiversity in the Pyrenees region and compare the results with previous studies. Additionally, the paper seeks to identify evolutionary phases within the Lochkovian. We analyse the stratigraphic range data from eight classical Pyrenean Lochkovian sections. A total of 48 taxa at the species level, primarily confined to the Lochkovian, are included in the analysis. We employ both qualitative and quantitative approaches, including Clark's method for the conodont evolution index and Foote's parameters for measuring taxonomic diversity and rates. The zonal scheme employed in this study follows the global three-fold subdivision of the Lochkovian stage, with additional subdivisions based on local records. The zone-by-zone analysis of stratigraphically well-controlled successions contributes to our understanding of the conodont diversity dynamics in this region. The results are consistent with previous studies, but also highlight the unique aspects of the Pyrenean conodont record. Their highest diversity occurs in the middle Lochkovian within the kutscheri-pandora beta Zone, succeeded by an extinction event towards the end of this interval. Following a brief proliferation of species at the onset of the upper Lochkovian, another extinction event concludes this Stage. Results from all different rate measurements applied to Pyrenean Lochkovian conodonts are in disagreement with the prevailing perspective suggesting an escalation in the proportion of singletons and a concomitant decline in per-taxon rates with an increase in interval length. Comparative analysis of conodont records across various regions (Carnic Alps, Prague Synform, Central Nevada, and the Pyrenees) during the Lochkovian reveals significant differences in biodiversity, taxonomic composition, and zonal distribution.

Upper Triassic (middle Norian) conodont biostratigraphy succession from Qamdo, eastern Tibet

The Late Triassic is a critical period that witnessed major biological and environmental events. The geographic range and taxonomic diversity of conodonts were significantly changed during the Late Triassic, with the geographic range contracting prior to complete extinction of the group near the end of the Triassic. In the present study, we recognize for the first time a continuous middle Norian (Upper Triassic) conodont succession from the Qamdo (Changdu) area, eastern Tibet (Xizang), which was part of the North Qiangtang and Qamdo-Simao Block (NQ-QSB) located in the northeastern Tethys Ocean during the Late Triassic. Four conodont zones are established from the middle Norian (Alaunian) of the Chaiwei section in Qamdo, and in ascending order these are: the Epigondolella spiculata Zone, the Orchardella elongata Zone, the Mockina postera Zone, and the E. serrulata Zone; the neighboring Tuoba section also records these four zones, in addition to the upper lower Norian (upper Lacian) Ancyrogondolella uniformis Zone. All of these zones (except for the M. postera Zone) have been recognized for the first time in eastern Tibet. The Lacian-Alaunian boundary is tentatively placed at the level of sample CW-3 at the Chaiwei section and at the level of sample TBL-36 at the Tuoba section by the first occurrence (FO) of E. spiculata in each section. The position of the Alaunian-Sevatian boundary (ASB) is uncertain since the conodont assemblage from the top of the Bolila Formation at the study sections lacks age-diagnostic elements. The conodonts recovered from the Qamdo area have not only dated the Bolila Formation but also refined the conodont biostratigraphic zonation of the Alaunian in the study area. This allows improved correlation between the faunas of Qamdo and their counterparts elsewhere in Tibet and Europe, although the conodont zonations from these regions display lower precision than those established from North America. The Alaunian conodont faunas at Chaiwei and Tuoba appear to be dominated by juvenile specimens; this often appears to be the case in the Alaunian of the Tethyan Realm, but seems not occur in North America. This may suggest that the conodonts living in these two realms may have inhabited different ecological environments. The faunal turnover around the Lacian-Alaunian transition, with the evolution of Epigondolella, Orchardella, and Mockina from Ancyrogondolella, can be recognized in both study sections, although it is more remarkable in the Tuoba section. Although the lack of previous detailed studies of Norian conodont biostratigraphy from Tibet hampers correlation in this region and beyond, this study demonstrates the possibility of establishing high-resolution conodont biostratigraphic successions from Tibet in the future, since the conodont faunas recognized from Tibet and adjacent areas (e.g., Baoshan) suggest that relatively complete Norian strata exist in these regions. Overall, this study also provides new data to improve our understanding of conodont evolution during the Alaunian, and is significant in providing palaeontological data for studying the palaeogeographic evolution of eastern Tethyan ocean basins in the Late Triassic.

Shape diversity in conodont elements, a quantitative study using 3D topography

The flourishment of conodont diversity through the Paleozoic is evidenced by the strong diversification of the shape of the elements composing their feeding apparatus. Among the different elements that compose the feeding apparatus, the platform elements (P1) are the most robust. However, the P1 elements also represent the most posterior dental elements of the apparatus, performing therefore the ultimate stage of food processing before ingestion of the food bowl. Thus, characterizing the shape of these elements across various species of conodonts could be relevant to decipher the diversity of feeding behavior among this group. Here we use topographic indices initially developed for the description of teeth relief (RFI, Slope), orientation (OPCr) and sharpness (ARC, DNE) to discriminate quantitatively P1 element shapes among conodont communities of the Late Famennian from the Montagne Noire Area (south France). We evidence methodological considerations such as voxel size impact on topographic indices that should be imperatively considered before conducing these methods on conodonts. Under several homogeneous conditions, this quantification of shape diversity, even on poorly damaged specimens, could bring new clues for the understanding of P1 elements kinematics and feeding strategies among conodonts.

Appraisal of middle Floian (Lower Ordovician) conodont diversity of the Precordillera and Cordillera Oriental, Argentina: Paleobiogeographical implications

In this paper we compare the diversity of Floian (Lower Ordovician) conodonts from the Precordillera with that of the Cordillera Oriental, Argentina. The comparative analysis is restricted to the middle Floian Stage Slice (Fl2) from correlative intervals: Oepikodus evae Zone (Juanognathus variabilis Subzone) in the Precordillera and the Gothodus andinus Zone in the Cordillera Oriental. For the comparative analysis, absolute frequency tables of the conodont data from published articles and collections under study, were prepared. These include four sections of the Precordillera with 13 samples recovered from the middle section of the carbonate San Juan Formation, and six sections of the Cordillera Oriental with 28 samples from the middle-upper section of the shaly Acoite Formation. Diversity patterns and indices were generated from absolute frequencies using the software PAST 4.03. Remarkable differences in the species richness and diversity between coeval communities of referred basins are displayed. Comparisons with other basins elsewhere suggest that the paleolatitudinal gradient is not a major factor controlling changes in diversity, which may be due to a response to the complex interaction of biological and physico-chemical factors.

Upper Norian conodonts from the Baoshan block, western Yunnan, southwestern China, and implications for conodont turnover.

The Sevatian of the late Norian is one of the key intervals in biotic turnover and in changes of paleoclimate and paleoenvironments. Conodont faunas recovered from two sections of upper Norian strata of the Dashuitang and Nanshuba formations near Baoshan City in western Yunnan province provide new insights into the diversity and biostratigraphy of the Sevatian conodonts within China as well as globally. A lower Mockina (M.) bidentata Zone and an upper Parvigondolella (P.) andrusovi Zone are identified in this area according to the first occurrences of M. bidentata and of P. andrusovi. Rich conodont fauna of M. zapfei is detailed and presents various intraspecific forms. A total of 19 forms of P1 elements are presented, which, when combined with the reported conodonts in the M. bidentata Zone, suggest that there was a peak in conodont diversity within the M. bidentata Zone. A biotic crisis in the uppermost M. bidentata Zone is recognized from the contrast between the diverse conodont fauna in the M. bidentata Zone and the rare conodonts in the P. andrusovi Zone. The conodont turnover during the middle Sevatian highlights the fact that the prolonged phases of the end-Triassic mass extinction probably began in the transition interval from M. bidentata Zone to P. andrusovi Zone.

The middle–late Tournaisian crisis in conodont diversity: a comparison between Northeast Laurussia and Northeast Siberia

The middle–late Tournaisian (Hastarian–Ivorian) transition is marked by isotopic and sedimentological evidence of climatic cooling and glaciations accompanied by a sea level fall and changes in global ocean circulation. At this time, the extinction among conodonts was followed by its gradual recovery in the late Tournaisian–early Viséan. Siphonodellids, representing an important part of conodont assemblages in the early–middle Tournaisian, became extinct. This study aims to compare conodont diversity dynamics in Northeast Laurussia and Northeast Siberia. The materials used range in paleolatitudinal gradients from 20°N (the north of the Urals and Pechora Craton) up to 45°N (Northeast Siberia), and in paleoclimatic gradient from an equatorial to a warm subtropical climate. The middle and late Tournaisian conodont associations of these regions demonstrate a high similarity in taxonomic composition and diversity dynamics, which may suggest that the glaciation and the following decrease in temperature probably was not the direct cause of conodont extinction; instead, the changes in the food web implied by the carbon isotope compositions of conodont elements and host carbonates could have been the main driver of the crisis in conodont diversity

Ordovician conodont biostratigraphy, diversity and biogeography in deep-water radiolarian cherts from Kazakhstan

Studies of conodonts from the ribbon-banded radiolarian cherts and siliceous siltstones in the Burubaital Formation in the Buruntau area (SW Balkhash region, Kazakhstan) made it possible to characterize the conodont fauna from deep-water environments in the Ordovician. The conodont assemblages from chert successions at times of high diversity document at least 53 taxa (39 species and 14 taxa identified in open nomenclature) for the entire Ordovician. Conodont biodiversity in the Floian and lower Darriwilian is comparable to the diversity of conodonts inhabiting the neritic zone of epicontinental basins and continental shelves. In the Dapingian and from the middle Darriwilian to the end of the Ordovician, the taxonomic diversity of deep-water conodonts in Kazakhstan is lower and comprises no more than five–six species in total. Stratigraphic distribution of conodonts in the Burubaital Formation sections along with their distribution in the previously studied chert localities in Kazakhstan were used as a base to estimate the succession of conodont zones in deep-water siliceous deposits. The resulting conodont zonation is based on cosmopolitan conodont species and allows broad correlation with deposits of several other paleocontinents.The pelagic habitat of the Early Ordovician oceans is subdivided into two latitudinal biogeographical units - tropical, recorded in Siberia, Laurentia and adjacent terranes, and temperate to cold climate zone, recorded in Baltoscandia, Avalonia and Western Gondwana. The low gradient between the climate of high and low latitudes confirms that the climate in the Early Ordovician was warmer than in the Middle Ordovician.

Evidence of parallel evolution in the dental elements of Sweetognathus conodonts.

The repeated emergence of similar morphologies in the dental elements of Permian Sweetognathus conodonts has been a hypothesized example of parallel evolution. To test if morphological parallelisms occur between isolated Sweetognathus lineages, this study uses two-dimensional-based geometric morphometrics combined with a revised and expanded phylogeny of Permian Sweetognathus conodonts to quantify dental element trait distributions and compare the phenotypic trajectories between lineages. A hierarchical clustering method was used to identify recurrent species pairs based on principal component scores describing their morphological variation, with the further incorporation of widely used ecological metrics such as limiting similarity and morphological overlap. Our research implies that a major contributor to conodont diversity in Palaeozoic marine trophic networks is the emergence of recurrent parallel morphologies via disruptive and directional selection. This study illustrates the mechanisms through which conodonts achieved their status as hyper-diverse predators and scavengers, contributing substantially to the complexity of Palaeozoic marine communities.

Global climate changes account for the main trends of conodont diversity but not for their final demise

Conodonts, one of the longest-lived early groups of vertebrates, have a very complete fossil record ranging from the late Cambrian to the end of the Triassic and persisted through many global climatic and biotic events. In this paper, we analyse a large dataset harvested from the Paleobiology Database to compute global diversity curves at the generic level and explore patterns of conodont paleogeographic distribution. Our results partly confirm the most prominent findings of earlier studies including the occurrence of an Ordovician acme, a Permian nadir and a short-lived Triassic recovery. Major peaks of origination were found in the Early Ordovician and Early Triassic, while major extinctions occurred in the Upper Ordovician and Pennsylvanian. Paleogeographical extent of conodonts was impacted by i) the position of paleo-continents (notably impacting the latitudinal gradient of diversity), ii) the available continental shelf area and iii) ice sheets expansion. Diversity trends were mostly impacted by transitions between hothouse and icehouse ages, with major glaciations and associated marine regressions co-occurring with major extinctions. The influence of global sea level was less marked than that of temperature. However, the final demise of conodonts at the end of the Triassic did not coincide with either a major glaciation or marine regression. This supports the view that extinction of the group was mostly due to biotic factors such as competition with ‘Mesozoic’ taxa.

Quantifying the community turnover of the uppermost Wenlock and Ludlow (Silurian) conodonts in the Baltic Basin

The Homerian to Ludfordian interval of the mid to late Silurian Period was a time of significant changes in conodont communities, global climate, oceanographic patterns and biogeochemical cycles. The Mulde and the Lau events are preeminent examples of globally recognized conodont extinction episodes from this interval in Earth's history. The Silurian Baltic Basin is the most suitable locality, globally, for studying these perturbations to the ocean-atmosphere system, since there is an extensive record of conodont taxa occurrences, their communities, and their environments spanning across shore-face to open-ocean settings. In this study, we present new conodont and δ13C data from the upper Homerian to Ludlow interval from two core sections – Gėluva-99 and Gėluva-118, representing shelfal environments, and the numerical conodont data from the Viduklė-61 section, from deep-water settings, and compare them with patterns of conodont diversity change, as revealed in the data-rich Milaičiai-103 core section. For this purpose, we explored the stratigraphically tied time series of conodont diversity changes employing recurrence and cross-recurrence plots – the binary similarity matrices that are used for deciphering complex spatial and temporal dynamic patterns. The cross-recurrence plots were used as a means of synchronizing the geological sections by applying dynamic time warping and the newly described moving window median recurrence point search algorithms. The results revealed that the conodont community compositional data are sufficiently temporally and spatially coherent to be reasonably used for synchronizing geological records. Moreover, the sudden state transitions detected in the cross-recurrence plots suggest that the Lau Event was of great importance for conodont community evolution in the studied time slice.

Dynamics of the conodont diversity in the Late Devonian–Early Carboniferous (Famennian–Serpukhovian)

Subject.The article is aimed to evaluate of the conodont diversity dynamics at the species level in the Famennian – Serpukhovian interval.Materials and methods.The database compiled from the published and original data contains information on the stratigraphic ranges of 389 Famennian-Serpukhovian conodont species (https://1drv.ms/x/s!AvPFMTPLPc7T4nFU81CaO5UJ6nlw). Conodont zones compose the geochronological basis of the database. The conodont diversity, origination, extinction, and diversification were calculated. Dynamics of these parameters in the Late Devonian–Early Carboniferous was analyzed.Results.The Famennian-Serpukhovian conodonts demonstrate four cycles in the diversity: the early Famennian (triangularis-early postera zones), the late Famennian (late postera-praesulcata zones), the Tournaisian (sulcata-anchoralis zones), and the Visean-Serpukhovian (texanus-bollandensis zones). The cycles are separated by the low-diversity episodes. The highest diversity (80 species) is detected in the early and late marginifera zones (Famennian).Conclusions.The successive decreasing in diversity comprises interval from the late Famennian through Serpukhovian. The global events gave little influence on the conodont diversity except for the Frasnian/Famennian (about 70% conodont species became extinct) and Devonian/Carboniferous extinction events. Conodont diversity demonstrates weak dependence form the global sea level fluctuations. The transition from the green-house to ice-house climate at the beginning of the Carboniferous and successive changes in the marine ecosystems are considered as main probable cause of the decline in conodont diversity in the late Tournaisian-Serpukhovian.

Conodont size reduction and diversity losses during the Carnian Humid Episode in SW China

The enigmatic biotic and environmental changes during the Carnian Humid Episode (CHE) have been investigated in South China. The body size of conodonts, assessed as length of P1 elements, and their diversity show substantial changes in the mid-Carnian. The well-dated Long Chang, Yongyue and Caizitang sections in southwestern China record a change of palaeoenvironments from shallow-marine carbonate platforms to deeper, euxinic basins. All sections show a major loss of conodont diversity and abundance late in the Julian 1 at a time of rapid warming and marine anoxia. Conodont size saw a reduction in maximum, mean and minimum size during the Julian 2 to Tuvalian 2 interval caused by the short-lived appearance of small species and a size decrease of the survivors. Conodont mean size reduction coincided with marine euxinia or anoxia and temperature fluctuations during the Julian 2 to Tuvalian 2 interval. Carnian conodonts thus follow Bergmann's Rule: element size is inversely correlated to the temperature. Climate warming with the consequential development of marine anoxia or euxinia is probably directly responsible for biotic changes at this time. Supplementary material: Conodont length data from the Long Chang (LC), Yongyue (NR) and Caizitang (CZ) sections and data for the cross plot between estimated temperature and conodont mean size in the Long Chang section are available at https://doi.org/10.6084/m9.figshare.c.4114424

Conodonts and ostracodes from the late Tournaisian bathyal sequence of the Polar Urals

Abstract Early Carboniferous (late Tournaisian) conodonts, recovered from siliceous shales and silicites of the Nyan- Vorga Formation within the Lemva tectonic belt of the Polar Urals (Russia), include the biostratigraphically important taxa Siphonodella lanei, Gnathodus typicus, Dollymae hassi, and Scaliognathus anchoralis, marking the following conodont zones of the upper Tournaisian: crenulata, typicus, and anchoralis. Associated species include representatives of genera Siphonodella, Polygnathus, Pseudopolygnathus, Dollymae, Gnathodus, Kladognathus, and Idioprioniodus. These conodont faunas provide the first biostratigraphically constrained correlations between bathyal deposits of the Lemva Allochthone in the Polar Urals and the “standard” conodont zonation. Ostracodes found in the silicite of the typicus Zone are represented by Sagittibythere ? sp. and Tricornina (Bohemia) sp. The ostracodes are reported from the bathyal deposits of Urals for a first time. The traces of the global Mid-Aikuanian Event are recognized in the upper part of the Tournaisian bathyal succession. This event led to turnover in conodont associations and is followed by increasing in conodont diversity.

Конодонты из пограничных артинско-кунгурских отложений разреза Мечетлино (Башкортостан, Южный Урал). Статья I. Характеристика конодонтовых комплексов

The description of the section of Artinskian-Kungurian boundary deposits on Yuryuzan River right coast near the village Mechetlino is given. The low systematic diversity and vare low frequency of conodonts in the Artinskian-Kungurian interval in the Uralian sections are noted, which is an order of magnitude inferior to the representativeness of conodonts in the Asselian and Sakmarian Stages. Nine informative levels with conodonts in the ten-meter section, revealed by Mechetlino quarry, give the possibility to trace the stratigraphic distribution of the species from the sweetognatid and neostreptognathodid chronoclines and to find out morphological trends in the development of these groups of conodonts. The basic morphotypes of conodonts are described. The phylogenetic tendencies in the evolutionary development of the representatives of genera Sweethognathus and Neostreptognathodus are shown, on the basis of which is built the zone conodont scale for this stratigra­phic interval and the lower boundary of Kungurian stage at the level of the appearance of the species Neostreptognathodus pnevi Kozur et Movschovitsch is established. The distribution of the conodont’ complexes in the section is shown, the dynamics and charakteristics of its change with time are analyzed. The Sarginskian horizon of Artinskian stage is identified well on the appearance of conodonts of the species-cosmopolite Neostreptognathodus pequopensis Behnken. This species loses teeth on the anterior part of the parapets and passes in N. pnevi Kozur et Movschovitsch. The species N. ruzhencevi Kozur appear together with N. pequopensis Behnken. N. ruzhencevi Kozur undergo in the Kungurian century the analogous metamorphosis, which led to the reduction of carinal tooth-edges on the anterior parts of the parapets. Such forms are isolated in the independent species N. lectulus Chern. The level of the appearance of the species N. pnevi and N. lectulus coincides with lower boundary of Kungurian stage.

Harnessing stratigraphic bias at the section scale: conodont diversity in the Homerian (Silurian) of the Midland Platform, England

AbstractFossil abundance and diversity in geological successions are subject to bias arising from shifting depositional and diagenetic environments, resulting in variable rates of fossil accumulation and preservation. In simulations, this bias can be constrained based on sequence‐stratigraphic architecture. Nonetheless, a practical quantitative method of incorporating the contribution of sequence‐stratigraphic architecture in community palaeoecology and diversity analyses derived from individual successions is missing. As a model of faunal turnover affected by the stratigraphic bias, we use the ‘Mulde event’, a postulated mid‐Silurian interval of elevated conodont turnover, which coincides with global eustatic sea‐level changes and which has been based on regionally constrained observations. We test whether conodont turnover is highest at the boundary corresponding to the ‘event’ and post‐‘event’ interval against the alternative that conodont turnover reflects habitat tracking and peaks at facies shifts. Based on the previously documented, parasequence‐level stratigraphic framework of sections in the northern and central part of the Midland Platform, the relative controls of sequence‐stratigraphic architecture, time and depositional environment over conodont distribution are evaluated using permutational multivariate analysis of variance. The depositional environment controls the largest part of variability in conodont assemblage composition, whereas the postulated ‘Mulde event’, or genuine temporal change in conodont diversity, cannot be detected. Depending on the binning of the stratigraphic succession, contrasting diversity and turnover patterns can be produced. The simple approach proposed here, emulating partitioning of β diversity into spatial and temporal components, may help to constrain the stratigraphic bias, even at the scale of an individual section.

Testing hypotheses of element loss and instability in the apparatus composition of complex conodonts: articulated skeletons ofHindeodus

AbstractKnowledge of the conodont skeleton, in terms of the morphology of the elements and the positions they occupy, provides the foundation for understanding of homology, taxonomy and evolutionary relationships in conodonts. This knowledge also underpins analyses of conodont functional morphology and feeding. Direct evidence of skeletal anatomy and apparatus architecture comes from natural assemblages: fossils that preserve together the articulated remains of the conodont apparatus, either collapsed onto a bedding plane or as clusters of elements in which juxtaposed and overlapping elements have been fused together by diagenetic minerals. Here we describe six clusters of the biostratigraphically important conodontHindeodus parvusfrom the Lower Triassic Shangsi section, Sichuan Province, South China. Five of these clusters represent the partial remains of articulated skeletons, providing direct evidence of the number and arrangement of elements in the apparatus. Combined with data from previously published natural assemblages this provides a test of the hypothesis that Triassic conodonts had a reduced dentition.Hindeodus parvuspossessed a complete raptorial array of two M and nine S elements (unpaired S0; symmetrically paired S1, S2, S3, S4); the paired P1locations were occupied by carminiscaphate elements, but the apparatus lacked P2elements. This is consistent with broader evidence for a particularly high degree of integration and constraint operating on the S–M array of morphologically complex conodonts, leading to conserved architecture of the array over a period of more than 250 million years. The loss of elements from the P domain implies a change in food processing ability and, given the predominance of data from P elements in conodont taxonomy and biostratigraphy, the hypothesis of element loss from the P domain has significant implications for the broader understanding of conodont diversity and evolutionary patterns.

Examining the Ladinian crisis in light of the current knowledge of the Triassic biodiversity changes

Several mass extinctions are known from the history of life, but knowledge about “minor” biotic crises remains incomplete. The Ladinian is the second stage of the Middle Triassic epoch. Available reconstructions of the diversity dynamics of fossil organisms across the entire Triassic allow the proposed Ladinian biotic crisis to be investigated. Total biodiversity curves (both the conventional curve and that based on sampling standardization) fail to identify the crisis, but this may be explained by low resolution data or “noise”. In fact, the global generic diversity of ammonoids, brachiopods, and tetrapods declined significantly (by 1.1–2.5 times) during the Ladinian, as did the species diversity of conodonts. Bivalves radiated, but their origination rate also decreased during the Ladinian. Land plants were apparently unaffected. Based on the representative regional record for the Northwestern Caucasus, the number of macroinvertebrate genera dropped by ~7.5 times, and brachiopods almost totally disappeared; foraminifers were also affected significantly. Thus, the proposed biotic crisis appears to have been selective. It appears the Ladinian biotic crisis was a relatively long-term event, and its magnitude is comparable to that of other “minor” mass extinctions, e.g., those of the Silurian, Early Jurassic, or end-Cenomanian. There are several possible explanations for what caused the Ladinian biotic crisis. It is possible that global climate cooling was responsible, although it is unclear why the palaeobiogeographical differentiation was not favourable for a biotic radiation. A eustatic explanation for the drop in diversity is unlikely. Instead, the crisis was mostly likely caused by unstable recovery of the Earth's biota after the end-Permian catastrophe.

Conodont diversity across the late Eifelian Kačák Episode of the southern Alpine realm (central Carnic Alps, Austria/Italy)

The polyphased Kačák Episode near the Eifelian-Givetian boundary (Middle Devonian), well documented globally, resembles other global biotic extinction events driven by climate change. High-resolution conodont biodiversity patterns from shallow marine, slope and pelagic bathymetric settings within the same basin from the Carnic Alps show that while conodonts experienced diversification during the latest Eifelian ensensis Biozone, assemblages suffered extinction during the early Givetian hemiansatus Biozone. Although a similar general pattern is observed in different bathymetric settings there is a changed taxonomic composition of conodont assemblages across the stage boundary. Based on microfacies analysis this change is contemporaneous with changes in palaeoenvironmental conditions in the earliest Givetian.