Hirnantia Fauna Research Articles

Heterogeneous palaeo‐ecogeography of brachiopods during the Late Ordovician mass extinction in South China

AbstractFollowing the first phase of the Late Ordovician mass extinction (LOME), the globally distributed Hirnantia brachiopod fauna exhibited homogeneity both latitudinally and longitudinally. The uniform global palaeobiogeography of the Hirnantia fauna, based solely on occurrence data, might obscure its heterogeneous nature during the glaciation. In this study, leveraging diversity and abundance data from well‐sampled collections in South China, along with non‐metric multidimensional scaling (NMDS) using the Raup–Crick measure, network analysis (NA), and abundance models, we unveil the palaeo‐ecogeography of the Hirnantia fauna for the first time. The distribution of the Hirnantia fauna in South China is categorized into three areas: the deep water area, the shallower water area, and the very shallow water area, based on NMDS and NA. Drastically different benthic assemblages among these areas reveal diverse environmental settings, with an approximate westward shallower trend and a deeper trend extending both northward and southeastward. Analysis of species‐abundance models for eight well‐sampled collections demonstrates different best‐fitted models, suggesting that competitive ecology operated in varied contexts despite common BA3 environmental settings and close geographical proximity. While a substantial global sea level fall and climate cooling around the Katian–Hirnantian boundary played important roles in the LOME, the palaeo‐ecogeography of the Hirnantia fauna in South China was predominantly influenced by the expansion of the Cathaysian oldland and the Qianzhong uplift. The interval between the two LOME phases, marked by kinetic conditions, witnessed the heterogeneous development of the Hirnantia fauna.

The deep-water, high-diversity Edgewood-Cathay brachiopod Fauna and its Hirnantian counterpart

The last phase of the end-Ordovician extinction event involved substantial sea-level changes. The Oslo/Asker District in Norway is a rare place where the deeper-water early Hirnantian fauna is succeeded by the equivalent deeper-water Edgewood-Cathay Fauna. Both faunas are highly diverse, with the same small-shelled brachiopods, Onniella, Leangella, and Eoplectodonta, dominating. They also share a large number of long-ranging and eurytopic genera. Taxa from contemporary shallower-water environments are rare. Near a third of the brachiopod genera in the Norwegian deeper-water early Hirnantian Fauna went extinct, including seven genera that survived into the Ordovician/Silurian boundary strata. Deeper-water early Hirnatian and Edgewood-Cathay collections are not well-known worldwide. Global quantitative samples from low latitudes, including the Norwegian samples, were compared against each other using NMDS (Non-metric Multidimensional Scaling) with the Bray-Curtis index. Qualitative samples used NMDS with the Raup-Crick index and Network Analysis. The Raup-Crick index sharply differentiated the early Hirnantian and Edgewood-Cathay faunas, possibly due to sensitivity to extinction and origination data. In contrast, the paleogeographic affinity between collections of the two faunas is pronounced using the Bray-Curtis index. Network Analysis also demonstrates regionality; the Edgewood-Cathay Fauna is especially heterogeneous. This contrasts with the shallower-water Hirnantia Fauna, which is more cosmopolitan. Quiet waters below the storm-wave base possibly hindered the spread of larvae, and anoxic plumes of water may have caused further barriers to the lateral spreading of the Edgewood-Cathay Fauna. As in Norway, long-ranging, eurytopic taxa were shared between the two faunas with few typical shallow-water taxa.

Timeline of events in the Ordovician–Silurian Transition of the Precordillera (Argentina): Paleoenvironmental, paleoclimatic and paleobiologic implications

This paper aims at analyzing the Ordovician–Silurian (Hirnantian–early Llandoverian) Transition in the Central and Eastern Precordillera of San Juan Province based on stratigraphic relationships, diagnostic deposits and sedimentary, paleobiologic and isotope data. At the Central Precordillera, three sections have been examined and sampled: (a) Los Baños de Talacasto, (b) Poblete Norte in the Talacasto area, and (c) northward the Cerro La Chilca section. At the Eastern Precordillera, only the Don Braulio section at the Villicum Range has been considered. These four sections have been selected because they include significant brachiopod assemblages related to the three Transitional Benthic Faunas (TBF 1–3), Hirnantian and Rhuddanian graptolites zones and palynomorph assemblages, in addition to isotope data as a useful tool for dating and correlations. The analysis of these sections has allowed recognizing the timeline of four events that span early Hirnantian–early Llandoverian. Event 1 is linked to the early Hirnantian postglacial transgression, in accordance with TBF 1 and Metabolograptus extraordinarius Zone correlation. Event 2 developed in the middle-upper Hirnantian, is witnessed in a transgressive shallow-water succession, coeval with the Hirnantia Fauna and Metabolograptus persculptus Zone. Event 3 is widely represented by the basal cherty pebbly conglomerate of La Chilca Formation and its correlatives Los Bretes and lower Tambolar formations in the Central Precordillera. This conglomerate is thought to be a lag deposit, which erosively overlies Ordovician strata, as a result of the Hirnantian postglacial transgression, but it is absent in the Eastern Precordillera. Finally, Event 4, at the Villicum section, spans the late Hirnantian–early Llandoverian, standing out a shallow-water, bioturbated mudstone succession, of 12 m thick with no diagnostic fossils, indicating upwelling processes and probably including the Ordovician–Silurian Boundary. However, in the Los Baños de Talacasto and Poblete Norte sections, this succession is composed of a graptolite-rich pelite succession 12 m thick, exhibiting at the base Fe-phosphate strata, and bearing graptolite assemblages of the Hirnantian Metabolograptus persculptus Zone, and the Rhuddanian Parakidograptus acuminatus Zone, indicating the Ordovician–Silurian boundary. It should be noted that the A. ascensus Zone has not been registered to date in the Precordillera.

Latest Ordovician to earliest Silurian graptolites of northwest Peninsular Malaysia

AbstractGraptolites from the latest Ordovician to the earliest Silurian rocks of northwest Peninsular Malaysia are described and reviewed. The fossils were collected previously by C. R. Jones and presently by the authors inside the black mudstones from the basal section of Tanjung Dendang Formation in Pulau Langgun, Langkawi, which comprises assemblages from the Hirnantian Metabolograptus extraordinarius Biozone to the Rhuddanian Akidograptus ascensus–Parakidograptus acuminatus Biozone. The latest Ordovician strata also include a Hirnantia fauna bed between the Metabolograptus extraordinarius and Metabolograptus persculptus biozones, in which shelly fossils such as Mucronaspis sp. could be recovered. A revised graptolite biozonation is proposed for the latest Ordovician to the earliest Silurian succession of northwest Peninsular Malaysia. This interval is significant for understanding the extent of mass extinction events happening right at the end of the Ordovician period and subsequent faunal change in the region.

A low-diversity, silicified Hirnantia Fauna from Butuo, southwestern Sichuan, on the western margin of Yangtze Platform

The latest Ordovician Hirnantia Fauna is distributed worldwide including South China, but with very few records from the western margin of the Yangtze Platform. A silicified Hirnantia Fauna from the uppermost Tiezufeike Formation in the Laoga section, Butuo County, southwestern Sichuan, enriches the fauna’s record and warrants the recognition of the upper part of the Tiezufeike Formation as the Kuanyinchiao Bed. Etching bulk limestone samples from this level with acetic acid yielded 275 specimens of Dalmanella testudinaria, Plectothyrella crassicosta, and Hindella crassa. The population dynamics are analyzed for three successive populations in the section. Size-frequency histograms and survivorship curves indicate gradual improvement of the palaeoenvironments during the end of the Late Ordovician glaciation. The low-diversity brachiopod assemblages recognized in our study are assigned to the Dalmanella-Plectothyrella Community (DP Community) according to their dominant species. It is comparable with two other examples of DP communities, one from the neighboring Guizhou Province of Southwest China, and the other from the Baltica Region.

Carbon isotope chemostratigraphy and sea-level history of the Hirnantian Stage (uppermost Ordovician) in the Oslo–Asker district, Norway

AbstractWe present a δ13Ccarb chemostratigraphy for the Late Ordovician Hirnantian Stage based on 208 whole-rock samples from six outcrops in the Oslo–Asker district, southern Norway. Our data include the Norwegian type section for the Hirnantian Stage and Ordovician–Silurian boundary at Hovedøya Island. The most complete record of the Hirnantian Isotope Carbon Excursion (HICE) is identified in a coastal exposure at Konglungø locality where the preserved part of the anomaly spans a c. 24 m thick, mixed carbonate–siliciclastic succession belonging to the upper Husbergøya, Langåra and Langøyene formations and where δ13Ccarb peak values reach c. +6 ‰. Almost the entire HICE occurs above beds containing the Hirnantia Fauna, suggesting a latest Hirnantian age for the peak of the excursion. The temporal development of the HICE in southern Norway is associated with substantial shallowing of depositional environments. Sedimentary facies and erosional unconformities suggest four inferably fourth-order glacio-eustatically controlled sea-level lowstands with successively increased exposure and erosion to the succession. The youngest erosional unconformity is related to the development of incised valleys and resulted in cut-out of at least the falling limb of the HICE throughout most of the Oslo–Asker district. The fill of the valleys contains the falling limb of the HICE, and the postglacial transgression therefore can be assigned to the latest part of the Hirnantian Age. We address the recent findings of the chitinozoan Belonechitina gamachiana in the study area and its relationship to the first occurrence of Hirnantia Fauna in the studied sections, challenging identification of the base of the Hirnantian Stage.

From shallow to deep water: an ecological study of the Hirnantia brachiopod Fauna (Late Ordovician) and its global implications

A large brachiopod fauna collected through the upper Wanyaoshu Formation (middle Hirnantian), West Yunnan, China displays, for the first time, a vertical transition within the Hirnantia fauna. The inner to mid-shelf Fardenia–Hirnantia association segues into the deeper water Aegiromena–Anisopleurella association during the Metabolograptus persculptus marine transgression. This transition parallels the pattern apparent in onshore–offshore gradients within the Hirnantian, imitating Walther’s Law for facies, instead predicting the seaward transitions between community types within a single transgressive sequence. In addition, large-sized brachiopods such as Hirnantia and Eostropheodonta become rarer and small-sized brachiopods, for example, Aegiromena and Anisopleurella more common. It is a rare opportunity to view transformations in community composition and structure within the Hirnantia fauna together with changes in both the size of individuals and populations (from large to small) during the transgression.

The latest Ordovician Hirnantia brachiopod fauna of Myanmar: Significance of new data from the Mandalay Region

A new, latest Ordovician brachiopod fauna is systematically described from the Hwe Mawng Purple Shale Member (Hirnantian) of the Naungkangyi Group of the Pa-thin area, Mandalay Region, Myanmar, revealing one of the most diverse representatives of the typical Hirnantia Fauna. Rhynchonelliformean, craniiformean and linguliformean brachiopods studied belong to 23 genera and a few indeterminate taxa, among which the most abundant genus Kinnella, along with the four common genera (Paromalomena, Pseudopholidops, Fardenia, and Dalmanella), and other genera (such as Cliftonia, Draborthis, Hindella, Hirnantia, Leptaena, Mirorthis, Plectothyrella, Skenidioides, and Xenocrania) are recorded for the first time. This high diversity Hirnantia Fauna represents an ecological differentiation within the benthos of the Sibumasu Terrane during the end Ordovician global crisis. The palaeoeco-unit named herein as the Kinnella-Paromalomena Association is assigned to lower BA3. This paper includes a taxonomic revision with the following conclusions: 1) Sinomena Zeng et al. and Yichangomena Zeng et al. are treated as junior synonyms of Eostropheodonta Bancroft; 2) Hubeinomena Zeng et al. is regarded as a juvenile form of Coolinia Bancroft; 3) Paramirorthis Zeng et al. is considered an immature growth stage of Mirorthis Zeng; 4) Shanomena Cocks and Fortey is treated as a junior synonym of Paromalomena Rong; 5) Scenidium? medlicotti Reed is redesignated as the type species of Kinnella Bergström to replace Hirnantia? kielanae Temple. The distribution of the Hirnantia Fauna in Myanmar, Thailand and western Yunnan of the Sibumasu Terrane highlights the distinctive nature of the Mandalay fauna, and the analyses of the Hirnantia Fauna and others of Sibumasu shows that Sibumasu was not located far from the South China and Lhasa palaeoplates during late Middle and Late Ordovician.

A latest Ordovician Hirnantia brachiopod fauna from western Yunnan, Southwest China and its paleobiogeographic significance

A new, high-diversity, latest Ordovician brachiopod fauna of nearly 800 brachiopod specimens was collected from the Wanyaoshu Formation (Hirnantian) in the Shaodihe section, Mangshi City, western Yunnan, Southwest China. Altogether 22 genera and two undetermined taxa were identified; dominant are Aegiromena, Anisopleurella, Fardenia, Dalmanella, Hirnantia and Hindella, less common, Paromalomena, Leptaena, Eostropheodonta, Cliftonia, Kinnella, Templeella and Plectothyrella, together with some rare Petrocrania, Xenocrania, Pseudopholidops, Palaeoleptostrophia, Skenidioides, Giraldibella, Draborthis, Dolerorthis and Toxorthis. This is one of the most diverse typical Hirnantia faunas, associated with the Kosov Province. The paleobiogeographic relationships between western Yunnan (Southwest China), Myanmar, Yichang (Central China), Tibet (Southwest China) and Kazakhstan are clarified using Network Analysis and NMDS. The fauna studied is most similar to that of Myanmar; both resided on the Sibumasu terrane. However, the recalculated network diagram, when including the data of Hirnantia fauna from the Prague Basin, indicates that the latter is more closely linked to that of western Yunnan, a testament to the very weak brachiopod provincialism during the Hirnantian, mainly due to the influence of dominant cosmopolitan taxa. Some species of the fauna display significant population variation. Two of the dominant taxa, Aegiromena and Anisopleurella are systematically described, whereas the other two common taxa, Fardenia and Hirnantia are measured and their outlines and internal structures analyzed.

A new Cathaysiorthis (Brachiopoda) fauna from the lower Llandovery of eastern Qinling, China

AbstractFollowing the end Ordovician mass extinction, brachiopod faunas were commonly of low diversity, generally rare in abundance, and restricted to shallow‐water environments in many places. The Cathaysiorthis fauna, first described from South East China, is the most diverse brachiopod fauna in the world succeeding the Hirnantia fauna, and has modified our previous views on the recovery of shelly benthos after the extinctions. Here, we report a newly‐discovered fauna with abundant Cathaysiorthis from the lower Zhangwan Formation (lower–middle Rhuddanian, lower Llandovery) in Qinling, Xichuan County, Henan Province, China. This fauna is slightly younger than that previously documented from South East China, and the evolution of Cathaysiorthis fauna, in terms of its composition, is discussed. The Qinling Cathaysiorthis fauna has a narrower bathymetric range (Benthic Assemblage Zone 3) than that of the fauna from South East China (BA 2–5) and occurred on the Qinling–Dabie Microplate located on the northwest margin of the South China Plate. The migration of the Cathaysiorthis fauna from the South China plate to Qinling–Dabie was achieved by larvae that used ambient ocean currents and possibly drifted from the Jiangnan Region of South East China to Qinling. The Qinling Cathaysiorthis fauna includes 13 species belonging to 12 genera. Two new species, Cathaysiorthis xichuanensis sp. nov. and Aegiria apta sp. nov. are established and described herein, and ten other species are discussed.

A new craniid brachiopod genus from the terminal Ordovician Hirnantia fauna of Myanmar and South China

AbstractHirnantian costate craniides are rare in the world; many have only been defined using open taxonomic nomenclature and assigned to the genera Acanthocrania and Philhedra. New material from South China and Myanmar allows establishment of a new genus, Xenocrania, including its type species Palaeocyclus? haimei Reed from the Hirnantia fauna in northern Shan State, Myanmar. This genus is characterized by a unique ornamentation with a large degree of intraspecific variation in sympatric and allopatric populations. Three types of ornamentation (A, B and C) are recognized within the same population of this species, and even on the same individual. Based on this high degree of variation, we consider Xenocrania haimei and Acanthocrania yichangensis Zeng from the Hirnantia fauna of Yichang, western Hubei, South China to be conspecific. X. haimei was probably an opportunistic species, exhibiting considerable significant phenotypic pleiotropy (exemplified by a highly variable ornament) in response to severe ecological stress, particularly during the end Ordovician crisis, enabling the species to survive the extinction event. Geographically, Xenocrania gen. nov. occurs not only in the Hirnantia fauna of Myanmar (Sibumasu) and South China, but also in England (Avalonia), Poland (Baltica) and probably also Bohemia (Perunica). A further reassessment of many nominal or indeterminate taxa of Ordovician and Silurian craniides tentatively attributed to Philhedra, Acanthocrania and other related genera is needed.

A deep water shelly fauna from the uppermost Ordovician in northwestern Hunan, South China and its paleoecological implications

It is the first time to document the trilobite Mucronaspis ( Songxites ) wuningensis and the brachiopod Paromalomena - Aegiromenella Assemblage from the Xinkailing Bed (Hirnantian, uppermost Ordovician) in Taoyuan and Cili counties, northwestern Hunan Province. Synecological analysis shows that this is a deep water shelly fauna of South China during the Hirnantian. It lived on the upper Jiangnan Slope in northwestern Hunan, adjacent to the southeast margin of the Upper Yangtze Region, and belongs to the Hirnantia fauna with cool and deep water, and low diversity affinity, similar to its contemporary shelly faunas from the southern Shaanxi Slope adjacent to the north margin of the Upper Yangtze Region, the northern Chongqing depression (new name), and the Jiangxi-Anhui-Jiangsu gentle slope of the Lower Yangtze Region. Paleoecologically, it could be attributed to the BA 4–5 benthic regime (about 60–150 m deep, and deepest to 200 m), and was significantly different from the trilobite M . ( S .) mucronata and the typical Hirnantia fauna while the latters may have habited in BA 2–3 benthic regimes (about 5–60 m deep). A new paleogeographic distribution pattern of the Hirnantian shallow and deep water shelly faunas of South China is herein proposed for the first time. Assuming that the depositional rate was constant in northwestern Hunan during the end Ordovician, the duration of the Xinkailing Bed might be only 12 thousand years according to the thickness of the Wufeng Formation and the absolute age values of those relevant graptolitic biozones. Such a short time interval may indicate that the global environmental change during the crisis was much shorter than previously thought, and its influence on the deep water regime was significantly shorter than that on the shallow water regime.

Exploring the end‐Ordovician extinctions in Hirnantian near‐shore carbonate rocks of northern Guizhou, SW China: A refined stratigraphy and regional correlation

Richly fossiliferous Hirnantian shelly strata of near‐shore facies in northern Guizhou, South China, known as the Kuanyinchiao Formation, superbly record glacioeustatic sea‐level fluctuations and benthic faunal turnover. Recent studies of the temporal and spatial distribution of these carbonates and shelly fossils permit a critical stratigraphic revision and establishment of a robust regional stratigraphic correlation. The formation is revised to include three informal subdivisions, that is, units A, B, and C, in ascending order. Unit B of the formation typically is dominated by peloidal or oolitic grainstones, and unit C is composed of skeletal wackestone and calcareous mudstone, both units sharing distinctive coral and brachiopod faunas. This contrasts sharply with unit A of the formation, consisting of mudstone, silty mudstone, or calcareous mudstone, that yields the cool‐water Hirnantia fauna and associated coral fauna. In view of the presence of carbonate ooids and peloids, rugose corals, and a distinctive brachiopod assemblage, all indicative of warm‐water conditions, unit B, as well as unit C yielding the same shelly fauna, is interpreted as representing postglacial sedimentation immediately following the major Hirnantian glaciation, thus marking a significant climatic shift. Similar warm‐water carbonate rocks have been recognized in a number of regions along the margin of the Qianzhong Oldland, including Bijie, Renhuai, Tongzi, and Fenggang of northern Guizhou. Such a vast distribution area of these rocks indicates that postglacial carbonates are more widespread on the Yangtze Platform of South China than previously thought, providing a rare window into rocks and fossils of the survival interval immediately following the extinction event associated with the Hirnantian glacial episodes.

Biostratigraphical constraints on the disconformity within the Upper Ordovician in the Baoshan and Mangshi regions, western Yunnan Province, China

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.

Cornulitids (tubeworms) from the Late Ordovician Hirnantia fauna of Morocco

Two species of cornulitids, Cornulites gondwanensis sp. nov. and C. aff. shallochensis Reed are described from the Hirnantian of Morocco, within an assemblage representative of the Hirnantia brachiopod fauna occurring near the Ordovician South Pole. The dominance of aggregated and solitary free forms could be explained by particular sedimentary environments preceding the Hirnantian glaciation and the latest Ordovician Extinction Event. The diversity of cornulitids in the Late Ordovician of Gondwana and related terranes was relatively low, and less diverse than the cornulitids of Laurentia and Baltica. Hirnantian cornulitids from Morocco do not resemble Late Ordovician cornulitids of Baltica and Laurentia. Moroccan cornulitids seem to be closely allied to some older Gondwanan cornulitids, especially Sardinian ones. They resemble species described from the Late Ordovician and Llandovery of Scotland suggesting a palaeobiogeographic link.

What caused the five mass extinctions?

Although a majority of biologists are convinced that a mass extinction is underway on earth today, the human history with direct observatory data is too short to predict its future trends. At least five mass extinctions occurred during the Phanerozoic Eon, causing the rapid extinction of at least 75% of existing marine species; they also seriously affected species diversity on land once the terrestrial ecosystem developed. The causes and consequences of these mass extinctions have become the most useful analogs for understanding whether the current global ecosystem is experiencing an extinction event. Previous multidisciplinary studies of the extinction patterns of fossil groups and concurrent environmental changes of the five mass extinctions during the past 500 million years (occurring in the end-Ordovician, Late Devonian Frasnian-Famennian, end-Permian, end-Triassic, and end-Cretaceous) suggested that no catastrophic event wiped out all organisms on earth. However, all five mass extinctions were associated with serious environmental deterioration and major paleoclimatic changes. The end-Ordovician mass extinction, occurring 445.2–443.8 million years ago, consists of two phases separated by an interval dominated by the cold Hirnantia fauna. The wax and wane of glaciation and associated widespread anoxia were the major causes of the two phases of the end-Ordovician mass extinctions. The Late Devonian mass extinction consists of a few different events from the Givetian to the Devonian-Carboniferous boundary, of which the most important is the Kellwasser event around the Frasnian-Famennian boundary. This extinction most seriously affected the coral and stromatoporoid reefs, and caused the extinction of two brachiopod orders (Pentamerida and Atrypida). As of yet, there is no consensus on the cause of this extinction event. Global cooling related to the widespread development of the terrestrial vegetation ecosystem and marine anoxia are the two most plausible scenarios. Although impact events were reported from a few horizons in the Late Devonian, they cannot account for the multiple phases of the Late Devonian mass extinctions. The end-Permian mass extinction about 252 million years ago has been universally documented as the most serious, which caused the disappearances of about 95% of all marine and 75% of all terrestrial species. Based on the latest high-precision geochronology data from South China, this extinction happened within an interval of less than 61 thousand years. This extinction was associated with a sharp negative excursion of δ 13Ccarb. A rapid temperature rise of 6–8 °C also occurred within the extinction interval. The Siberian Traps eruption and volcanism in South China, triggered by the dispersal of the supercontinent Pangea, is the most plausible explanation for the end-Permian mass extinction. The end-Triassic mass extinction at 201.564±0.015 Ma also seriously affected both marine and terrestrial ecosystems. Amphibians and reptiles both suffered a great loss during this extinction, and they were subsequently replaced by highly diverse dinosaurs. Marine conodonts and Ceratitida became extinct, and the sponge Demospongea and the brachiopod order Spiriferinida were also greatly affected. Recent studies suggest that the extinction stage may have extended over 10–20 million years, and the volcanism of the Central Atlantic Magmatic Province may be the cause. The end-Cretaceous mass extinction has been the best-known event among the general public because it caused the extinction of various dinosaurs that prevailed during the Mesozoic Era. The cause of this extinction has been documented as the extraterrestrial Chicxulub impact event. However, detailed paleontological studies suggested that the extinction is more likely to have been caused by another major volcanism event, the massive eruption of the Deccan Traps. In summary, global changes in atmospheric CO2 and paleotemperature (both icehouse and greenhouse), oceanic acidification, sea-level changes, and anoxia triggered by massive volcanic eruptions are the most plausible causes of the past extinctions. Massive volcanism not only ejected a huge amount of CO2 and volcanic sulfates, but also caused a massive release of thermogenic CO2 and methane stored in the deposits of inland basins and continental shelves. Extraterrestrial impact, supernova explosion, and solar flares could instantaneously wipe out all organisms on earth, but they are not the main causes of the five mass extinctions experienced in the history of the earth.

New data on Hirnantian (latest Ordovician) postglacial carbonate rocks and fossils in northern Guizhou, Southwest China

The Kuanyinchiao Formation (Hirnantian, Upper Ordovician), yielding the typical Hirnantia fauna, has commonly been accepted as representing cool-water sediments deposited during the glacial interval in the Hirnantian Global Boundary Stratotype Section and Point (GSSP) region of South China. Recent investigation reveals that the uppermost carbonate-dominated part of this formation yields a warm-water rugose coral fauna with Silurian affinities at many localities of northern Guizhou Province, which substantially differs from the underlying cool-water fauna. This suggests that these carbonates were probably postglacial warm-water sediments, rather than having formed during the Hirnantian glacial interval as previously thought. Such a conclusion is consistent with the evidence from the associated brachiopod fauna, i.e., the Dalmanella testudinaria – Dorytreta longicrura community, which is similarly distinct from the underlying typical Hirnantia fauna. The sedimentological data show warm-water features at the same level (e.g., the presence of oolitic grains), also supporting this new interpretation.

Geographic distribution and palaeogeographic reconstruction of the Upper Ordovician Kuanyinchiao Bed in South China

The Kuanyinchiao Bed (Hirnantian, Upper Ordovician) is mostly composed of argillaceous limestone and yields the world-famous, cold-water shelly fauna—‘ Hirnantia fauna’. It occurs between two black shale units—the Wufeng and Lungmachi formations, and is widely distributed in the Upper Yangtze region of South China. Its consistent lithology, unique fauna, and wide distribution, make it an important maker bed for the stratigraphic subdivision and correlation of regional Ordovician-Silurian boundary rocks, both in outcrop and in drill core. Identification of the Kuanyinchiao Bed is especially important in the recognition of the Wufeng and Lungmachi black shales in the shale gas investigation in South China. Palaeogeographic reconstructions of the occurrence of the Kuanyinchiao Bed can enhance our understanding of the palaeogeographic background of the Late Ordovician mass extinction and the formation of the Wufeng and Lungmachi black shales.

Post-Glacial Hirnantian (Upper Ordovician) Bryozoans from Western Argentina: Implications for Survival and Extinction Patterns

Abstract. Two bryozoan taxa occurring in the Hirnatian (Upper Ordovician) deposits in western Argentina document a first postglacial community associated with a mid-to high-latitude brachiopod assemblage, known as the typical Hirnantia fauna, in the Argentine Precordillera. Helopora fragilis Hall and an indeterminate phyloporinid occur within a thin but conspicuous shell bed that overlies diamictitic deposits from the lower member of the Don Braulio Formation. The abundance of well preserved specimens of bryozoans together with the dominance of suspension feeders suggests a mid-shelf setting (offshore transition) with an intermediate to low sedimentation rate, low turbidity, and nutrient-rich conditions. Hirnantian bryozoan assemblages identified from tropical and subtropical regions are rather rare, and this assemblage represents the first high-latitude Hirnantian record. The low diversity of bryozoans may be related to high-latitude location of Argentina during the Late Ordovician. Helopora Hall occurs ...

Cladal Turnover: the end‐Ordovician as a large‐scale analogue of species turnover

AbstractModern studies of individual populations have shown large cyclical shifts in phenotype/genotype that correlate with climatic variations. At the hierarchical level of the species, similar patterns can be observed in the climatically mediated turnover of species (i.e. Vrba's Relay Model). In turn, mass extinction events may have a similar analogous relationship with species turnover, while operating at the clade level. In this paper, such an analogous process is described and named ‘the Cladal Turnover Model’. The end‐Ordovician mass extinction event is used as a test case to investigate the existence of such a phenomenon, with specific focus on the origin and extinction of the Hirnantia fauna. A test is outlined that can be applied to determine whether Cladal Turnover is occurring in the end‐Ordovician. An example case study is then performed on the Hirnantia trilobite genus ‘Brongniartella’. The results of this test suggest that while the taxon ‘Brongniartella’ is derived from putatively cold‐water high‐latitude stock (consistent with the classical definition of Hirnantia taxa), the group does not go extinct at the end‐Ordovician event, but instead gives rise to warm‐water low‐latitude descendants. This result is consistent with the Cladal Turnover Model. The method proposed for testing the Cladal Turnover Model could be applied to look at other times of major evolutionary turnover preserved in the fossil record.