Distribution Of Brachiopods Research Articles

Is there synchronicity between brachiopod diversity changes and palaeobiogeographical shifts across the Late Ordovician mass extinction?

AbstractAs the first major biotic event in the Phanerozoic, the two‐phased Late Ordovician mass extinction (LOME) resulted in a substantial decline in marine benthic biodiversity and heralding shifts in palaeobiogeography. However, the interplay between palaeobiogeographical distribution and biodiversity dynamics during this event remains unknown. Drawing upon brachiopod occurrence data from five intervals pre‐ and post‐LOME, extracted from the Paleobiology Database, we conducted a comprehensive analysis of palaeogeographic units across the extinction event. Through examination of generic diversity, origination and extinction rates, and biogeographic connectedness, we elucidate the evolutionary trajectories of both endemic and cosmopolitan taxa throughout the extinction. Our findings indicate increased vulnerability of endemic taxa to biotic events and their aftermath relative to their cosmopolitan counterparts. Notably, we observe a concordance between shifts in the palaeogeographic distribution of brachiopods and fluctuations in their diversity during and after the LOME. Moreover, the extinction and subsequent recovery dynamics of brachiopods during this event demonstrate temporal symmetry concerning biodiversity change and palaeobiogeographic structural shifts. Shortly after the extinction event, within a timeframe similar to the decline in diversity and contraction of palaeogeographic distribution, both aspects revert to pre‐extinction levels, suggesting the limited intensity of the LOME event.

Состояние изученности и корреляционный потенциал раннекаменноугольных брахиопод западного склона севера Урала

The article presents a brief history of Mississippian brachiopod studies in the North of the Urals during the last 175 years. The regional stratigraphic chart of the Western Urals subregion was originally developed on the basis of brachiopod biostratigraphy. The works of A. Keyserling, G. N. Fredericks, N. V. Kalashnikov, N. V. Enokyan, N. N. Fotieva, D. V. Nalivkin, and other researchers have greatly contributed to the study of the Mississippian brachiopods of the region. The most active use of the North Urals brachiopods for the biostratigraphy of the region falls in the 60—70s of the last century and is mainly connected with the works of N. V. Kalashnikov. However, brachiopods are hardly studied in the southern part of the Tchernyshev Swell and in basins of the Vuktyl, Bolshaya Nadota, Kosyu, and Kharuta rivers. The modern techniques and recent advances in brachiopod research both in Russia and in the world are considered. Considering the changes in brachiopod systematics and Mississippian stratigraphy during the last 30 years, it is concluded that it is necessary to update the data on the taxonomic composition, paleogeographic and stratigraphic distribution of brachiopods in the North Urals region.

New records of brachiopods from the Lower Miocene deposits of the Qom Formation of the Isfahan province, Central Iran

The study presents new records of brachiopods from the Lower Miocene deposits of the Qom Formation from two sections, Bagh and Ramsheh in the Isfahan province, Central Iran. Three species, i.e. Argyrotheca bitnerae, Joania cordata, and Platidia anomioides, have been identified in the investigated material. All species are present in the Bagh section whereas in the material from Ramsheh A. bitnerae was not found. Although the species recognized here were already described from the Miocene of the Qom Formation, this is their first report from the localities of Bagh and Ramsheh, providing new data on the distribution of brachiopods in the Cenozoic of Iran.

Geomorphological, sedimentological, and ecological characterization of marine caves from Capraia Island (Tremiti Archipelago, southern Adriatic Sea, Italy): An integrated approach

Marine caves are sites of great interest from geomorphological and ecological viewpoints due to their significant environmental variability, being located at the boundary between marine and terrestrial domains. Most of the Mediterranean marine caves resulted from karst phenomena which widely affected the carbonate landscapes. At Tremiti Archipelago (southern Adriatic Sea, Italy), the karst activity is widespread, determining, in combination with existing tectonic features and long-term geomorphological evolution, the presence of several marine caves, partly or completely submerged. Two of these marine caves, located at Cala Caffè and Cala Sorrentino (Capraia Island), were considered for a multidisciplinary study focused on their geomorphological, sedimentological, and ecological characterization. These submerged blind-ended caves, located between 19 and 25 m water depth, show morphologies clearly linked to the tectonic-karst geomorphological setting. Superficial sediment samples were analyzed to derive grain size distribution, total carbon and nitrogen, isotopic ratios, living and dead benthic foraminifers, and dead brachiopods; water parameters were also considered. Sediment distribution showed a similar trend in the two caves, with finer textures, higher organic content in the inner stations, and increased biogenic components. Foraminifers showed a faunal change from the outer to the inner sectors associated with the decreasing grain size and the increased organic matter. Differently, the distribution of brachiopods did not display evident patterns; the differences in absolute abundance between the two sites were mainly attributed to the entrance dimensions and the morphology of the two caves, which deeply affected light penetration. This integrated approach demonstrated that geoforms, due to karst and tectonic processes, create small-scale coastal geomorphological habitats, greatly increasing biodiversity.

Brachiopods of the Carboniferous-Permian Boundary Deposits of the Kubalakh Section (Lower Reaches of the Lena River, Northern Verkhoyanie)

The paper presents new data on the vertical distribution of brachiopods in the Carboniferous-Permian boundary deposits (the Kubalakh Formation) of the Kubalakh section (lower reaches of the Lena River). The deposits of the Kubalakh Formation are divided by the valley of the Kubalakh Creek into two outcrops, which are suggested to be considered as subformations. A brachiopod complex Jakutoproductus protoverkhoyanicus Kaschirzew, Verchojania abramovi Makoshin, Verchojania cf. monstrosus (Ganelin), Verchojania sp., Cancrinella? alazeica Zavodowsky, Tornquistia kolymensis Afanasjeva, Tornquistia sp., Rhynoleichus sp., Rhynchopora sp., characteristic of the Jakutoproductus protoverkhoyanicus Zone of the Kygyltasian Horizon of the Verkhoyanie is recognized in the Lower Kubalakh Subformation. A brachiopod complex Jakutoproductus verkhoyanicus (Fredericks), Jakutoproductus crassus Kaschirzew, Waagenoconcha aff. wimani (Fredericks), Orbiculoidea sp., Rhynchopora sp., characteristic of the Jakutoproductus verkhoyanicus Zone of the Khorokytian Horizon of the Verkhoyanie is recognized in the Upper Kubalakh Subformation. Based on the data presented, the Carboniferous-Permian boundary should be drawn within the Kubalakh Formation, rather than at the base of the Tuora-Sis formation, as is was accepted on the basis of the latest Unified Regional Scheme of Permian Deposits in the Verkhoyansk-Okhotsk region.

The functional performance of productidine brachiopods in relation to environmental variables

Fossils are useful as palaeoenvironmental indicators when evaluated using large occurrence and lithology association data sets and/or functional morphology. However, when functional morphology is invoked on an ad hoc basis there exists a risk of circular reasoning. Performance spaces/landscapes constructed using biomechanical experiments can be used to tie performance to morphology quantitatively. They can be used to estimate fitness and function in specific environments by allowing multiple specific measures of function to be evaluated simultaneously. Absolute performance can be used to constrain palaeoenvironmental interpretations by detecting functional limits. We constructed a performance space with four variables (transport resistance, settling time, settling orientation and respiration potential) relating to hydrodynamic and metabolic variables. We combine new performance data with existing palaeoenvironmental interpretations and associated distributions of brachiopods of the suborder Productidina during the late Carboniferous and early Permian in the North American Midcontinent. Productidines were chosen because they lacked pedicles and relied on body and spine morphology to interact with their environment. Offshore dysoxia-associated taxa had increased resistance to sinking and proportionally larger lophophores, potentially improving survivorship in low-oxygen, soft substrate environments. Taxa associated with nearshore and oxygenated offshore environments display a range in performance consistent with a range of conditions, but all had proportionally smaller lophophores. Models that are less stable in high-velocity flows consistently settle in the correct convex down orientation if entrained, while more stable models did not. Our study suggests that as productidines radiated during the Carboniferous, they also differentiated within the performance space.

Effect of the Mid-Carboniferous event on the diversity of brachiopods in the Middle and Southern Urals

Research subject. In this study, the distribution of brachiopods in the Mid-Carboniferous boundary (MCB) sediments in the Middle and Southern Urals was investigated with the aim of determining the influence of the global Serpukhovian-Bashkirian minor mass extinction event on the diversity of these benthic organisms. Materials and methods . Brachiopods distributed over the most complete carbonate sections of the West-Uralian (Brazhka, Sokol, Martyanovo, Askyn, Lakly), Magnitogorskian (Khudolaz, Kalinino, Bolshoy Kizil) and the East-Uralian (Beklenishchevo, Cave gully, Brod-Klyuchiki, “Uralnerud-1” quarry) megazons were studies. Results. It was established that the diversity of the Giganto-productus-Striatifera brachiopod association reduced during the Late Serpukhovian, with the extinction of its dominant taxa having occurred during the Early and Middle Carboniferous boundary. During the Syuranian time of the Bashkirian Age, the Middle-Late Carboniferous Choristites association was formed. Further, in the Akavassian time, the diversity of brachiopods was restored. The consequences of the described event affected mainly the taxa of the species and genus taxonomic rank, and, to a much lesser extent, those of the family rank. On the western slope of the Urals, the maximum regression was recorded at the top of the Striatifera shell-rock layer of the Lower Carboniferous Staroutkinskian regional substage. On the eastern slope of the Urals, the brachiopod diversity characterizing the event in question can be clearly seen in the Late Serpukhovian. This dynamics was also manifested in the lowermost Pennsylvanian; however, it was obscured by the activation of regional tectonic factors. Conclusion. In the Middle and Southern Urals, the Mid-Carboniferous minor mass extinction event is recognized according to the dynamics of the genus and species diversity of bra-chiopods in the deposits of different facies.

Resource partitioning among brachiopods and bivalves at ancient hydrocarbon seeps: A hypothesis.

Brachiopods were thought to have dominated deep-sea hydrothermal vents and hydrocarbon seeps for most of the Paleozoic and Mesozoic, and were believed to have been outcompeted and replaced by chemosymbiotic bivalves during the Late Cretaceous. But recent findings of bivalve-rich seep deposits of Paleozoic and Mesozoic age have questioned this paradigm. By tabulating the generic diversity of the dominant brachiopod and bivalve clades-dimerelloid brachiopods and chemosymbiotic bivalves-from hydrocarbon seeps through the Phanerozoic, we show that their evolutionary trajectories are largely unrelated to one another, indicating that they have not been competing for the same resources. We hypothesize that the dimerelloid brachiopods generally preferred seeps with abundant hydrocarbons in the bottom waters above the seep, such as oil seeps or methane seeps with diffusive seepage, whereas seeps with strong, advective fluid flow and hence abundant hydrogen sulfide were less favorable for them. At methane seeps typified by diffusive seepage and oil seeps, oxidation of hydrocarbons in the bottom water by chemotrophic bacteria enhances the growth of bacterioplankton, on which the brachiopods could have filter fed. Whereas chemosymbiotic bivalves mostly relied on sulfide-oxidizing symbionts for nutrition, for the brachiopods aerobic bacterial oxidation of methane and other hydrocarbons played a more prominent role. The availability of geofuels (i.e. the reduced chemical compounds used in chemosynthesis such as hydrogen sulfide, methane, and other hydrocarbons) at seeps is mostly governed by fluid flow rates, geological setting, and marine sulfate concentrations. Thus rather than competition, we suggest that geofuel type and availability controlled the distribution of brachiopods and bivalves at hydrocarbon seeps through the Phanerozoic.

Brachiopod distribution through the Jurassic–Cretaceous transition in the western Tethyan pelagic realm: Example from the Bakony Mountains, Hungary

Brachiopods, together with ammonoids, were collected bed-by-bed from several sections in the Bakony Mountains. The sections, straddling the Jurassic–Cretaceous transition, yielded abundant and diverse brachiopod material (1277 specimens, 18 species), and this offered a possibility to determine the stratigraphic ranges of the brachiopod species. The dating of the sections by ammonoids was supported by micropalaeontological (calpionellid and nannofossil) investigations. Three sections straddling the Jurassic–Cretaceous transition with continuous record with good ammonoid biostratigraphic zonation are documented in detail. It is demonstrated that, according to the stratigraphical distribution recorded in the Bakony sections, the most abundant brachiopod species range continuously from the Tithonian to the Berriasian, i.e. no change or turnover appears at the Jurassic/Cretaceous boundary. Our results endorse those published from the Pieniny Klippen Belt of Poland and underscore that, at least in the intra-Tethyan realm, the brachiopod species invariably crossed the Tithonian/Berriasian boundary.

Distribution of brachiopods in the Lower Visean deposits in the Eastern Urals

Subject. This paper is aimed at investigating the distribution of brachiopods across the stratotypes of the Lower Visean regional substages and formations, as well as of the Upper Visean Zhukovsky regional substage, which are presently located in the East Uralian and Magnitogorskian megazones of the Eastern Urals. Materials and methods. Brachiopods were one of the most numerous groups of benthic organisms inhabiting the Early Carboniferous marine basins now located in the eastern Urals. This paper presents information on the distribution of brachiopods across the carbonate and carbonate-terrigenous facies of the Middle (Pokrovskoe, Zhukovo, Smolino, Brod-Kljuchiki) and Southern (Nizhnyaya Gusikha, Verkhnyaya Kardailovka, Kipchak, Ust-Grekhovka and Khudolaz) Urals sections.Results. It is found that Delepinеа lebedevi, D. comoides, Ovatia markovskii and Composita sp. were the domineering species during the Early Visean period. The Ust-Grekhovsky time marked the appearance of migrant species, which resulted not only in a decrease in the proportion of Delepinеа and Ovatia but also significantly changed the entire structure of the local brachiopod communities. The evolutionary transformation of the Ovatia genus at the Ust-Grekhovsky–Zhukovsky time boundary led to the appearance of the Linoprotonia genus and subsequently to the Globosoproductus genus (the first representative of the Gigantoproductini). The Zhukovsky period was characterized by a continuing reorganization of the composition and structure of the communities, featuring a change in the dominant taxa. The Linoprotonia and Globosoproductus genera became widespread. Rare representatives of the Gigantoproductus, Datangia and Semiplanus genera appeared.Conclusions. A direct correlation between the diversity of brachiopod associations and abiotic factors is found. The most diverse associations represented by the taxa of several orders, including Gigantoproductini, inhabited shallow-water environments with carbonate sedimentation. The evolution of brachiopods over the Early Visean and Zhukovsky periods of the Late Visean was characterized by natural succession in the composition of genera and species, with the most significant alteration having occurred in the Ust-Grekhovsky and Zhukovsky periods.

Devonian and Carboniferous Brachiopods and Biostratigraphy of Transcaucasia (Ending)

The brachiopods of the orders Lingulida, Craniida, Orthida, Pentamerida, Rhynchonellida, Chonetida, Spiriferida, Spiriferinida, and Athyridida from the Middle–Upper Devonian and Lower Carboniferous of the Nakhchivan Autonomous Republic of the Republic of Azerbaijan and adjacent areas of Armenia are monographically described. The zonal scale for the Devonian and Carboniferous of Transcaucasia is elaborated based on the taxonomic composition and distribution of brachiopods and considering the data on the associated foraminifers, stromatoporoids, tabulate and rugose corals, tentaculites, bivalves, nautiloids, bryozoans, crinoids, conodonts, ostracods, trilobites, and flora. The history of regional biostratigraphic studies is reviewed. The results of work enrich and specify paleontological substantiation of the stratigraphic and correlation scales of Transcaucasia and, in addition, are useful for covering the Devonian and Carboniferous stages of brachiopod evolution and for resolving the general issues of Paleozoic biostratigraphy, particularly, for the compiling the faunal characteristic of the Devonian–Carboniferous boundary deposits.

A new Dienerian (Early Triassic) brachiopod fauna from South China and implications for biotic recovery after the Permian–Triassic extinction

AbstractBrachiopods suffered severe extinction during the Permian–Triassic crisis, such that their diversity dropped to extremely low levels in the Early Triassic. Here we describe a new brachiopod fauna from the Dienerian of Lichuan, South China. This fauna consists of three monospecific genera, including one new genus and one new species: Lichuanorelloides lichuanensis gen. et sp. nov., Lissorhynchia sp. and Crurithyris sp. These brachiopods co‐occur with the ammonoids Ussuridiscus, Jieshaniceras, Hubeitoceras and Vishnuites, suggesting an early Dienerian age. The geographical distribution of brachiopods in family Norellidae during the Early Triassic suggests that a migration took place towards higher latitudes, which may have been caused by the extreme climate warming that prevailed during the Dienerian.

The eoorthid brachiopod Apheoorthina in the Lower Ordovician of NW Argentina and the dispersal pathways between the Andean and Mediterranean regions of Gondwana

The eoorthid brachiopod Apheoorthina is reported for the first time from the Lower Ordovician of NW Argentina. It is represented by a species similar to A. ferrigena from the Tremadocian of the Prague Basin, increasing the faunal affinities between the Central Andean Basin and the South European microcontinents, in particular the Bohemian region (Perunica). Nine out of the fourteen brachiopod genera reported from the Tremadocian of the Central Andean Basin (~64%) are shared with the Mediterranean region, four of which (~28%) have been recorded in the Prague Basin, and two (Kvania and Apheoorthina) are restricted to the Central Andes and Perunica. Dispersal pathways around Gondwana are analyzed in the light of major factors affecting large-scale distribution of brachiopods (environment, larval capacity for dispersal, oceanic currents). The presence in Apheoorthina aff. ferrigena of a well-preserved larval protegulum measuring 420 μm in width and 210 μm in length strongly suggests that this species had planktotrophic larvae capable of long-distance dispersal. According to recent ocean-atmosphere general circulation models for the Ordovician Period, the Central Andean margin was dominated by the cold-water Antarctica Current. Despite the complex non-zonal pattern produced by current deflections around the peri-Gondwanan microcontinents, the general westward circulation sense favoured larval dispersal from the Andean region to North Africa, Avalonia, the Armorican Terrane Assemblage, and Perunica. On the other hand, the eastwards flowing Gondwana Current connected the North Gondwana waters with the South American epicontinental seas, which could explain the reversed migration of some brachiopods.

Latest Pliensbachian –Early Toarcian brachiopod assemblages from the Peniche section (Portugal) and their correlation

In the present paper we describe the distribution of brachiopods in the proposed Toarcian GSSP (Global Boundary Stratotype Section and Point) at Peniche. We differentiated four assemblages in the stratigraphic interval from the upper Emaciatum Zone of the Pliensbachian to the Levisoni Zone of the Toarcian. Assemblage 1 clearly presents Northwestern European affinities, with many species that are also present in Southern England. In the last levels of the Pliensbachian and in the Mirabile Subzone (the first level of the Toarcian), Assemblage 2 contains taxa that still present Northwestern European affinities, but with a more restricted, even endemic, distribution. The majority of the species in these levels are known from the Iberian Range in Spain and other neighboring basins. An important faunal change takes place in the Semicelatum Subzone, coinciding with the base of the Cabo Carvoeiro Formation, giving rise to Assemblage 3. In this assemblage we observed a clear decrease in the size of the specimens, coinciding with the establishment of the Koninckella Fauna; this fauna is found in several localities in both Northwestern European and Mediterranean areas where the paleoenvironment is relatively deep or poorly oxygenated. Brachiopods disappear in Peniche just above the Polymorphum - Levisoni zonal boundary, as has been observed in several other localities in Western Tethys. Their renewal is marked by the presence of Soaresirhychia bouchardi several meters above the extinction level, constituting Assemblage 4.

Integrated brachiopod-based bioevents and sequence-stratigraphic framework for a Late Ordovician subpolar platform, eastern Anti-Atlas, Morocco

AbstractThe Upper Ordovician (Katian–Hirnantian) brachiopods of Tafilalt, eastern Anti-Atlas, are locally abundant, diverse and well preserved, providing a near-continuous record of faunal change on a high-latitude siliciclastic-dominated platform. A chronostratigraphic framework, based on brachiopod distribution and preservation in shell accumulation events and integrated with sequence stratigraphy, has been generated for the Katian interval, which has allowed correlation with the chitinozoan-based chronostratigraphic and sequence-stratigraphic framework erected for the central Anti-Atlas. In Tafilalt, two Katian (transgressive–regressive) composite depositional sequences,c. 60 and 170 m thick and related to third-order fluctuations in sea level, were unaffected by Hirnantian glaciogenic erosion. They were deposited on a mixed platform with a bryonoderm association dominated by brachiopods, bryozoans and echinoderms. Brachiopods developed in high-energy inner shelf areas, whereas bryozoans (mainly trepostomates and fenestrates) and pelmatozoans (cystoids and crinoids) dominated in low-energy outer shelf areas. Brachiopod accumulations mark distinct event surfaces, such as lag and event concentrations, hydraulic simple and composite concentrations related to transgressive surfaces, and hiatal condensed concentrations marking maximum flooding surfaces. The taphonomic condensation displayed by the Hirnantian Alnif Member, which onlaps the erosive base of glaciogenic tunnel channels, is explained as reworking and resedimentation of allochthonous, robust, biogenic hard parts sourced from the underlying (Katian) Ktaoua Group.

PREDATION ON MODERN AND FOSSIL BRACHIOPODS: ASSESSING CHEMICAL DEFENSES AND PALATABILITY

The post-Paleozoic decline of the diversity and abundance of rhynchonelliform brachiopods has been attributed to a variety of factors. Of the possible mechanisms invoked to explain the evolutionary decline and cryptic or antitropical distribution of brachiopods, predation has frequently been dismissed due to the potentially low energetic value and suspected nonpalatability or toxicity of brachiopod tissues. Herein we demonstrate that multiple invertebrate marine predators (crustaceans, echinoderms, and gastropods) are willing and able to consume brachiopods in laboratory settings without observable negative effects after ingestion. In addition, field samples indicate predation pressure on the living brachiopod population may be substantial. Although feeding trials are consistent with previous reports that bivalves are preferred prey relative to brachiopods, predation should not be dismissed as a potentially important factor in brachiopod ecology and evolution. The results presented herein reveal that in some cases brachiopods may be the intended target of predatory attacks, especially in habitats where mollusks are rare or absent. Examination of the fossil record of predation on rhynchonelliform brachiopods is consistent with this interpretation: evidence for drilling and repair of brachiopod shells is found throughout the fossil record in multiple lineages. While it is likely that predation traces on post-Paleozoic brachiopods are generally rare, there are multiple reports of fossil localities with anomalously high drill-hole or repair-scar frequencies. This suggests that although brachiopods may be unwanted prey in the presence of energetically more desirable targets, they do appear to be edible and subject to intense predator-prey interactions under certain conditions.

Size-frequency distributions of Joania cordata and Argyrotheca cuneata (Brachiopoda: Megathyrididae) from the Central Tyrrhenian Sea

Size-frequency distributions can support reliable inferences concerning population dynamics of brachiopods, but only a few data are available so far. In this study, length and width frequency distributions of dead specimens of the Recent brachiopods Joania cordata and Argyrotheca cuneata from the Marine Protected Area ‘Secche di Tor Paterno’, Central Tyrrhenian Sea, Italy (41°35′ N, 12°20′ E), are reported in order to add new data about size-frequency distributions of brachiopods. The studied specimens came from death assemblages in the coralligenous substrate, in the Posidonia oceanica meadows, and in the sand channels. The observed patterns vary from left-skewed (J. cordata) to right-skewed (A. cuneata), indicating respectively a low and high mortality of smaller individuals. Significant differences between the coralligenous substrate and the P. oceanica meadow were observed for both species, revealing a variation among different habitats. All length and width distributions are clearly polymodal, but the biological meaning of the peaks is difficult to interpret, as the two species seem to have a 2-year life span. A biometric analysis of shell sizes revealed that length and width are the most variable parameters during the growth of the animal.

Global diversity and endemism in Early Silurian (Aeronian) brachiopods

Silurian brachiopods of Middle Llandovery (Aeronian) ages are reviewed, and 215 genera are identified here, compared with 109 in the preceding Early Llandovery (Rhuddanian), indicating a recovery-radiation interval after the end-Ordovician mass extinction. The chief regions in which they are found are the continents of South China, Avalonia-Baltica, Laurentia and Siberia, which were all at tropical latitudes with the exception of Avalonia. In addition, the very large superterrane of Gondwana, although with patchy brachiopod distribution, included temperate faunas, as well as subtropical faunas (in Iran and Afghanistan). Aeronian brachiopods greatly increased in diversity, with dominance of four major groups: orthides and strophomenides (which had flourished previously in the Rhuddanian), pentamerides and atrypides (which became dominant in the Aeronian), and many newly evolved taxa, and occupied deeper water and wider ecological niches (level bottom and reef) than those in the Rhuddanian. Each of the continents has some endemic genera, but there is a greater proportion of them in South China, where some groups (such as the pentamerides and atrypides) are more diverse and others, such as the orthides, are much less common than elsewhere. Affinity indices (AI) show that two megaunits can be recognized: South China and Avalonia-Baltica-Laurentia (ABL); Siberia seems to have been loosely connected with ABL and even more loosely to South China presumably because of its geographical separation in the Northern Hemisphere. The separation of South China from the other megaunits is further supported by cluster analysis.

Taxonomic composition and environmental distribution of post-extinction rhynchonelliform brachiopod faunas: Constraints on short-term survival and the role of anoxia in the end-Permian mass extinction

Marine taxonomic losses during the end-Permian mass extinction were driven by physiological stresses from ocean warming, acidification, and anoxia that ultimately resulted from CO2 release from Siberian Traps flood volcanism. Despite abundant proxy evidence for anoxia, its role is not well resolved because the timing and selectivity of the extinction are better explained by warming and ocean acidification. We studied the taxonomic composition and spatial and temporal distribution of brachiopod-rich post-extinction faunas, which contain short-lived Permian survivors that lived at a key time during and immediately after the peak of the extinction, to elucidate the controls on survival and the role of anoxia. Holdover brachiopods primarily belong to extinct families and orders, not to long-term survivors, and their probability of short-term survival was a function of pre-extinction metapopulation size. Although short-term survival appears to have been stochastic, likely because of intraspecific variation in tolerance within larger metapopulations, opportunistic and possibly dysaerobic-tolerant genera thrived locally. Rhynchonelliform brachiopod distribution was patchy, both environmentally and temporally. They were more abundant in shallow-water settings, consistent with an oxygenated habitable zone, and their local demise often corresponded with the local development of low-oxygen conditions. Thus, although warming and acidification may have been the primary triggers of taxonomic loss, the addition of spatially and temporally variable anoxic conditions exacerbated physiological stress and contributed to ultimate extinction of short-lived survivors. The combination of the three stresses—warming, acidification, and anoxia—which act synergistically to negatively affect respiratory physiology of marine invertebrates, may explain the severity of the end-Permian extinction and provides a sobering analogue for modern ocean acidification and anoxic dead zones.

Late Ordovician brachiopod distribution and ecospace partitioning in the Tvären crater system, Sweden

Patterns of distribution and ecospace utilization of Late Ordovician brachiopods in a recently formed, contemporary meteorite crater are described and analyzed. Rhynchonelliformean brachiopod communities, dominated by a wide range of orthides and strophomenides, colonized the newly formed crater. At the crater rim communities were established early on, although the crater depression was not inhabited until deposition of the upper third of the remaining crater fill. The crater formed a protected but restricted microenvironment where sediments four times the thickness of the nearby basinal succession accumulated. Within this narrow space environments varied from shallow-water to deeper-waters, about 200m in depth, and from well oxygenated to hypoxic. Such varied environments generated a rough ecological landscape, facilitating niche partitioning across a relatively small geographic area. Analysis of the guild structure of the fauna permits explanation of a local biodiversity hotspot in otherwise low-diversity strata elsewhere in the Scandinavian region. The Tvären impact event had an important palaeobiologic effect upon the fossil record as it served as a local pump and reservoir for biodiversity. Moreover the development of new community types and narrowly-defined niches helped further drive both α and β biodiversity during a critical phase of the Great Ordovician Biodiversification Event.