Palaeobiogeographic distribution patterns and processes of Neochonetes and Fusichonetes (Brachiopoda) in the late Palaeozoic and earliest Mesozoic

The global palaeobiogeographic distributions of two resembling genera, Neochonetes and Fusichonetes (Brachiopoda), from the Carboniferous to Griesbachian are analysed. This analysis provides insight into the biotic response of two related genera to changing palaeoclimate, regional tectonics, and environmental crises. Neochonetes originated in the equatorial area in the Mississippian, and it mostly retained this position during the peak of the glaciation in the Carboniferous–Permian ice age (namely in the Pennsylvanian). Neochonetes then dispersed globally during the Cisuralian when the climate became warmer and the ice sheet started to retreat. In the Guadalupian and Lopingian, following the closure of the Ural seaway at the end of the Cisuralian and the regression at the end-Guadalupian, Neochonetes almost disappeared in the western part of Gondwana. Subsequently during the Lopingian the genus retracted to the middle- and low-latitude Palaeo-Tethys and Tethys. In comparison, Fusichonetes originated in the equatorial area in the late Guadalupian and was still present in that area in the Lopingian. Both genera occurred only in South China in the Griesbachian. It is inferred that this could be related, not only to the deteriorated palaeoenvironmental conditions (e.g., anoxia, global warming) leading up to the extinction of most of the Neochonetes and Fusichonetes species in other areas, but also to the better physiological adaptation of the smaller shells of Neochonetes and Fusichonetes species in South China.     

Permian–Triassic Osteichthyes (bony fishes): diversity dynamics and body size evolution

The Permian and Triassic were key time intervals in the history of life on Earth. Both periods are marked by a series of biotic crises including the most catastrophic of such events, the end‐Permian mass extinction, which eventually led to a major turnover from typical Palaeozoic faunas and floras to those that are emblematic for the Mesozoic and Cenozoic. Here we review patterns in Permian–Triassic bony fishes, a group whose evolutionary dynamics are understudied. Based on data from primary literature, we analyse changes in their taxonomic diversity and body size (as a proxy for trophic position) and explore their response to Permian–Triassic events. Diversity and body size are investigated separately for different groups of Osteichthyes (Dipnoi, Actinistia, ‘Palaeopterygii’, ‘Subholostei’, Holostei, Teleosteomorpha), within the marine and freshwater realms and on a global scale (total diversity) as well as across palaeolatitudinal belts. Diversity is also measured for different palaeogeographical provinces. Our results suggest a general trend from low osteichthyan diversity in the Permian to higher levels in the Triassic. Diversity dynamics in the Permian are marked by a decline in freshwater taxa during the Cisuralian. An extinction event during the end‐Guadalupian crisis is not evident from our data, but ‘palaeopterygians’ experienced a significant body size increase across the Guadalupian–Lopingian boundary and these fishes upheld their position as large, top predators from the Late Permian to the Late Triassic. Elevated turnover rates are documented at the Permian–Triassic boundary, and two distinct diversification events are noted in the wake of this biotic crisis, a first one during the Early Triassic (dipnoans, actinistians, ‘palaeopterygians’, ‘subholosteans’) and a second one during the Middle Triassic (‘subholosteans’, neopterygians). The origination of new, small taxa predominantly among these groups during the Middle Triassic event caused a significant reduction in osteichthyan body size. Neopterygii, the clade that encompasses the vast majority of extant fishes, underwent another diversification phase in the Late Triassic. The Triassic radiation of Osteichthyes, predominantly of Actinopterygii, which only occurred after severe extinctions among Chondrichthyes during the Middle–Late Permian, resulted in a profound change within global fish communities, from chondrichthyan‐rich faunas of the Permo‐Carboniferous to typical Mesozoic and Cenozoic associations dominated by actinopterygians. This turnover was not sudden but followed a stepwise pattern, with leaps during extinction events.     

CALIBRATED DIVERSITY,TREE TOPOLOGY AND THE MOTHER OF MASS EXTINCTIONS: THE LESSON OF TEMNOSPONDYLS

Abstract: Three family‐level cladistic analyses of temnospondyl amphibians are used to evaluate the impact of taxonomic rank, tree topology, and sample size on diversity profiles, origination and extinction rates, and faunal turnover. Temnospondyls are used as a case study for investigating replacement of families across the Permo‐Triassic boundary and modality of recovery in the aftermath of the end‐Permian mass extinction. Both observed and inferred (i.e. tree topology‐dependent) values of family diversity have a negligible effect on the shape of the diversity curve. However, inferred values produce both a flattening of the curve throughout the Cisuralian and a less pronounced increase in family diversity from Tatarian through to Induan than do observed values. Diversity curves based upon counts of genera and species display a clearer distinction between peaks and troughs. We use rarefaction techniques (specifically, rarefaction of the number of genera and species within families) to evaluate the effect of sampling size on the curve of estimated family‐level diversity during five time bins (Carboniferous; Cisuralian; Guadalupian–Lopingian; Early Triassic; Middle Triassic–Cretaceous). After applying rarefaction, we note that Cisuralian and Early Triassic diversity values are closer to one another than they are when the observed number of families is used; both values are also slightly higher than the Carboniferous estimated diversity. The Guadalupian–Lopingian value is lower than raw data indicate, reflecting in part the depauperate land vertebrate diversity from the late Cisuralian to the middle Guadalupian (Olson’s gap). The time‐calibrated origination and extinction rate trajectories plot out close to one another and show a peak in the Induan, regardless of the tree used to construct them. Origination and extinction trajectories are disjunct in at least some Palaeozoic intervals, and background extinctions exert a significant role in shaping temnospondyl diversity in the lowermost Triassic. Finally, species‐, genus‐, and family trajectories consistently reveal a rapid increase in temnospondyl diversity from latest Permian to earliest Triassic as well as a decline near the end of the Cisuralian. However, during the rest of the Cisuralian family diversity increases slightly and there is no evidence for a steady decline, contrary to previous reports.     

Evolution of Permian conodont provincialism and its significance in global correlation and paleoclimate implication

The main components of Asselian through Artinskian conodont faunas found around the world are basically the same, and the provincialism is indicated only by less common endemic elements such as Gondolelloides and New Genus A Henderson in North Pangea, Sweetognathus bucaramangus around the equator and Vjalovognathus in eastern Gondwana. Provincialism is marked by differences at the species level of Mesogondolella, Neostreptognathodus and Sweetognathus during the Kungurian, and becomes very distinct with differences at the genus level during the Guadalupian and Lopingian. Three provinces of Permian conodonts, referred to as the North Cool Water Province (NCWP), the Equatorial Warm Water Province (EWWP) and the peri-Gondwana Cool Water Province (GCWP), are recognized. The NCWP is marked by Gondolelloides in the early Cisuralian, dominance of Neostreptognathodus and no or rare Sweetognathus in the late Cisuralian, dominance of Merrillina and Mesogondolella and absence of Sweetognathus in the Guadalupian, and dominance of Merrillina and Mesogondolella and absence of Iranognathus in the Lopingian. The EWWP is characterized by the absence of Gondolelloides and Vjalovognathus in the Cisuralian, abundance of Sweetognathus and Pseudosweetognathus in the Kungurian (late Cisuralian), Jinogondolella and Sweetognathus in the Guadalupian, and Clarkina and Iranognathus in the Lopingian. The GCWP is marked by Vjalovognathus, Merrillina in the Cisuralian, Vjalovognathus, Merrillina and Mesogondolella in the Guadalupian, and Vjalovognathus and Merrillina in the Lopingian. Mixed faunas are recognized in regions bordering between the EWWP and GCWP including Western Timor during the Artinskian, Pamirs during the Kungurian and the Salt Range during the Guadalupian and Lopingian.

Three different conodont zonations are proposed, one for each of the three conodont provinces. Four potential horizons for inter-provincial correlation of Permian conodonts are recognized. They are in ascending order: (1) the first appearance of Sweetognathus whitei, which is closely related to the last occurrence of Carboniferous-type conodonts such as Streptognathodus and Adetognathus; (2) the first appearance of Neostreptognathodus pequopensis; (3) the base of the Jinogondolella nankingensis Zone; and (4) the base of the Clarkina postbitteri–Iranognathus erwini Zone.

The spatial and temporal distribution pattern of Permian conodonts suggests that temperature is the primary controlling factor. Evolution of Permian conodont provincialism reveals a glaciation during the Asselian and Sakmarian, a global warming during the Artinskian, a climate cooling in North Pangea during the Kungurian, a continuation of Kungurian climate trends in the Guadalupian, a relatively minor warming during the Wuchiapingian, a returned cooling in the Changhsingian and Lower and Middle Griesbachian, and a global warming in the Late Griesbachian, which ended the Permian conodont lineage.     

巴基斯坦盐岭地区二叠纪生物地层研究的新进展

近30年来,巴基斯坦盐岭地区的Wargal组和Chhidru组以及在喜马拉雅地区相当地层的地质时代被许多学者视为中二叠世(瓜达鲁普世)。根据华南与盐岭地区瓜达鲁普统和乐平统的牙形类化石带对比,可以确定Amb组和Wargal组底部的时代为瓜达鲁普世晚期,瓜达鲁普统与乐平统的界线位于Wargal组下部,吴家坪阶与长兴阶的界线位于Chhidru组的下部,而二叠与三叠系的界线位于Mianwali组下部的Kathwai段之内。我国西藏南部色龙群及相当地层含有与巴基斯坦盐岭地区Kalabagh段和Chhidru组可对比的乐平世腕足动物群以及二叠系—三叠系界线附近连续的牙形类化石带,由此可以推定色龙群的时代应为乐平世。     

Latest Guadalupian brachiopods from the Guadalupian/Lopingian boundary GSSP section at Penglaitan in Laibin, Guangxi, South China and implications for the timing of the pre-Lopingian crisis

A brachiopod fauna comprising nine species in eight genera from three closely spaced stratigraphic horizons of the same stratigraphic section is described for the first time from the Laibin Limestone in the uppermost part of the Maokou Formation in the Guadalupian/Lopingian (G/L) GSSP section at Penglaitan, Guangxi Autonomous Region, South China. The brachiopod assemblages are bracketed between two conodont zones: Jinogondolella xuanhanensis Zone below and Jinogondolella granti Zone above and, therefore, they can be safely assigned to the latest Capitanian in age. However, all but one of the nine brachiopod species from the Laibin Limestone carry strong early Lopingian (Wuchiapingian) aspect. Thus, the discovery of this brachiopod fauna not only suggests that some Lopingian brachiopod species had already appeared in the late Guadalupian (Capitanian); more importantly, it has also highlighted the fact that both the previously noted pre-Lopingian life crisis (or end-Guadalupian or Middle Permian mass extinction) and Lopingian recovery/radiation actually occurred in late Capitanian times, sometime before the G/L chronostratigraphic boundary. So far, the Penglaitan GSSP section provides the highest-resolution disappearance patterns of different fossil groups around the G/L boundary.     

Transgressive–regressive sequences on the slope of an isolated carbonate platform (Middle–Late Permian, Laibin, South China)

From the Middle to Late Permian, the Laibin area in Guangxi, South China, was situated on the slope of an isolated carbonate platform, on which continuous marine successions were deposited. Two global stratotype sections for the boundary between the Guadalupian (Middle Permian) and Lopingian (Late Permian) are located at Penglaitan and Tieqiao in the Laibin area, respectively, and thus are chosen for study. At the two locations, 14 facies are recognized in the Maokou and Heshan Formations, and they are further grouped into four facies associations (basin, lower slope, upper slope, and platform margin). Six main transgressive–regressive (TR) sequences are identified in strata from the Roadian (Middle Permian) to the Wuchiapingian (Late Permian). They are conformable marine sequences that were little influenced by regional uplift (Dongwu Movement) and so provide a good record of the sea-level changes in South China at this time. Based on the significant taxonomic selection and controversial marine faunal loss in the end-Guadalupian mass extinction, and the Middle-Late Permian sea-level changes recorded by the TR sequences in the Laibin area, it is suggested that this extinction event might have been triggered by the reduction and loss of shallow-marine habitat area caused by the end-Guadalupian regression. The global cooling and Emeishan volcanism also occurring at this time could have further enhanced this extinction event.     

Changhsingian (Late Permian) foraminifers from the topmost part of the Xiala Formation in the Tsochen area,central Lhasa Block,Tibet and their geological implications

A foraminiferal fauna consisting of 15 genera and 19 species is documented for the first time from the topmost part of the Xiala Formation in the Aduogabu area in Tsochen County, central Lhasa Block. This foraminiferal fauna is dominated by Colaniella, indicating a broadly Changhsingian age. The presence of Colaniella, Reichelina and absence of the typical tropical fusuline genus Palaeofusulina in the fauna indicate that the Lhasa Block has not merged into equatorial regions during the Changhsingian. More importantly, the widespread Lopingian (Late Permian) marine carbonates with warm-water faunas and the stable platform carbonate sequence through the Guadalupian and Lopingian in the Lhasa Block present an obvious contrast against the contemporaneous sequences in the South Qiangtang Block and Gondwana margin. It suggests that both the Bangong-Nujiang Ocean and the Neotethys Ocean would have opened by the Guadalupian and Lopingian.     

Global Taxonomic Diversity of Anomodonts (Tetrapoda,Therapsida) and the Terrestrial Rock Record Across the Permian-Triassic Boundary

The end-Permian biotic crisis (∼252.5 Ma) represents the most severe extinction event in Earth''s history. This paper investigates diversity patterns in Anomodontia, an extinct group of therapsid synapsids (‘mammal-like reptiles’), through time and in particular across this event. As herbivores and the dominant terrestrial tetrapods of their time, anomodonts play a central role in assessing the impact of the end-Permian extinction on terrestrial ecosystems. Taxonomic diversity analysis reveals that anomodonts experienced three distinct phases of diversification interrupted by the same number of extinctions, i.e. an end-Guadalupian, an end-Permian, and a mid-Triassic extinction. A positive correlation between the number of taxa and the number of formations per time interval shows that anomodont diversity is biased by the Permian-Triassic terrestrial rock record. Normalized diversity curves indicate that anomodont richness continuously declines from the Middle Permian to the Late Triassic, but also reveals all three extinction events. Taxonomic rates (origination and extinction) indicate that the end-Guadalupian and end-Permian extinctions were driven by increased rates of extinction as well as low origination rates. However, this pattern is not evident at the final decline of anomodont diversity during the Middle Triassic. Therefore, it remains unclear whether the Middle Triassic extinction represents a gradual or abrupt event that is unique to anomodonts or more common among terrestrial tetrapods. The end-Permian extinction represents the most distinct event in terms of decline in anomodont richness and turnover rates.     

Upper Permian coral reef and colonial rugose corals in northwest Hunan, South China

Summary The roles of Permian colonial corals in forming organic reefs have not been adequately assessed, although they are common fossils in the Permian strata. It is now known that colonial corals were important contributors to reef framework during the middle and late Permian such as those in South China, northeast Japan, Oman and Thailand. A coral reef occurs in Kanjia-ping, Cili County, Hunan, South China. It is formed by erect and unscathed colonies ofWaagenophyllum growing on top of one anotherin situ to form a baffle and framework. Paleontological data of the Cili coral reef indicates a middle to late Changhsing age (Late Permian), corresponding to thePalaeofusulina zone. The coral reef exposure extends along the inner platform margin striking in E-S direction for nearly 4 km laterally and generally 35 to 57 m thick. The Cili coral reef exhibits a lateral differentiation into three main reef facies; reef core facies, fore-reef facies, and marginal slope facies. The major reef-core facies is well exposed in Shenxian-wan and Guanyin-an sections where it rests on the marginal slope facies. Colonial corals are dispersed and preserved in non-living position easward. Sponges become major stabilizing organisms in the eastern part of Changhsing limestone outcrop in Kanjia-ping, but no read sponge reefs were formed. Coral reefs at Cili County in Human are different distinctly from calcisponge reefs in South China in their palaeogeography, lithofacies development, organic constitutuents, palaeoecology and diagenesis. The Cili coral reef also shows differences in age, depositional facies association, reef organisms and diagenesis from coral reefs in South Kitakami of Japan, Khorat Plateau of Thailand, and Saih Hatat of Oman. Although some sponge reefs and mounds can reach up to the unconformable Permian/Triassic boundary, coral reef at Kanjia-ping, Cili County, is the latest Permian reef known. This reef appears to had been formed in a palaeoenvironment that is different from that of the sponge reefs and provides an example of new and unique Permian reef type in South China, and could help us to: 1) understand the significance of colonial corals in Permian carbonate buildups; 2) evaluate the importance of coral community evolution prior to the collapse of reef ecosystems at the Permian/Triassic boundary; 3) better understand the effects of the biotic extinction events in Palaeotethys realm; 4) look for environmental factors that may have controlled reefs through time and space, and 5) provide valuable data for the study of Permian palaeoclimate and global evolutionary changes of Permian reefs and reef community.     

Timing and progression of the end-Guadalupian crisis in the Fars province (Dalan Formation, Kuh-e Gakhum, Iran) constrained by foraminifers and other carbonate microfossils

The Middle-to-Upper Permian in the Kuh-e Gakhum anticline (southeastern Iran) has rarely been studied due to its structural complexity and the difficult access. Rich Permian fusulinid assemblages varying in age from Wordian to Changhsingian were found in a thick carbonate succession corresponding to the Dalan Formation. Three new species of foraminifers are described and a new biostratigraphic framework including five biozones is proposed. One of these, described and defined for the first time in the Dalan Formation, is based on the presence of Praedunbarula simplicissima n. gen. n. sp. When compared to the fossil content of existing bioprovinces, the floro-faunal biota of the Dalan Formation shows an affinity with Central and Western Tethys. A mass extinction of fusulinids and small foraminifers (70%) occurred concomitantly with the onset of a relative sea-level fall. This event led to a change in the carbonate factories from biologically induced carbonate production to ooid-rich chemically induced precipitation. The morphology of the platform at the Guadalupian/Lopingian transition evolves from a bioclastic ramp to a shelf. This transition is also characterized by a major sequence boundary and morphological anomalies in foraminifers. Therefore, as the regression and the changes in floro-faunal contents have been observed at the Guadalupian/Lopingian boundary, the extinction event is considered as end-Guadalupian. It is followed by a Lopingian transgression yielding renewed foraminiferal assemblages.     

Correlation of the Middle and Upper Permian marine and terrestrial sedimentary sequences in Polish, German, and USA Western Interior Basins with reference to global time markers

Here we discuss the duration and position of Upper Rotliegend and Zechstein stratigraphic units in relation to the absolute time scale, and reinterpret a carbon isotope (δ¹³C) global event recorded from Late Permian (Lopingian/Guadalupian) marine deposits. Based on δ¹³C isotope correlation (chemostratigraphy) and of climatic evidence related to the end-Guadalupian global marine and terrestrial crisis, the Guadalupian/Lopingian boundary is proposed as the boundary between both the European Upper Rotliegend (URII)/Zechstein sediments and the parallel south-west USA Ochoan/Bell Canyon Formation units. The Zechstein deposition was strongly influenced by climatic oscillations, and the marine ingressions recorded in the North German Basin and North American Delaware Basin are presumed to have resulted from the same eustatic sea-level changes in western and northern coasts of the Northern Pangaea Supercontinent. Existing constraints on the age of the Upper Rotliegend II (UR II) deposits are imposed by the uncertainty of the chronostratigraphic boundary of the Kupferschiefer and by a time marker that is Illawarra, the boundary of the reversed polarity megachron (Kiaman) and mixed polarity megachron. Three options (A, B, C) have been discussed, which are connected with a time span comprising deposition of the UR II rocks, assuming that the time span needed for the Dethlingen/Lower Noteć formations and Hannover/Upper Noteć formations is about 6 myr. The time left for the deposition of the Parchim/Lower Drawa, Mirow/Upper Drawa deposits and the time hidden in the erosional gaps and hiatuses range from 1.6 myr to 4 myr or even 8 myr. These were based on the time interval related to the Kiaman Reversed Polarity megachron, which can contain more transient normal polarity zones than currently accepted. The presence and absolute dating of all such magnetozones is difficult to determine because they are represented in continental strata characterized by numerous, poorly time-constrained erosional gaps. The proposed option C is provisionally integrated with magnetostratigraphic results and shows an alternative stratigraphical scheme for the Upper Rotliegend. This alternate Upper Rotliegend stratigraphy helps correlate rocks (deposited in dry arid climatic conditions) in the lower part of the Upper Rotliegend II of the Southern Permian Basin (Havel and Drawa subgroups) with similar rocks in the Delaware Basin (attributed to formations within the Leonardian Regional Series).     

Late Paleozoic–early Mesozoic continental biostratigraphy — Links to the Standard Global Chronostratigraphic Scale

Nonmarine biostratigraphic/biochronologic schemes have been created for all or parts of the late Carboniferous–Middle Triassic using palynomorphs, megafossil plants, conchostracans, blattoid insects, tetrapod footprints and tetrapod body fossils, and these provide varied temporal resolution. Cross correlation of the nonmarine biochronologies to the Standard Global Chronostratigraphic Scale has been achieved in some parts of the late Carboniferous–Middle Triassic in locations where nonmarine and marine strata are intercalated, the nonmarine strata produce biochronologically significant fossils and the marine strata yield fusulinids, conodonts and/or ammonoids. Other cross correlations have been aided by magnetostratigraphy, chemostratigraphy and a growing database of radioisotopic ages. A synthetic nonmarine biochronology for the late Carboniferous–Middle Triassic based on all available nonmarine index fossils, integrated with the Standard Global Chronostratigraphic Scale, is presented here. The focus is on the nonmarine biostratigraphy/biochronology of blattoid insects, conchostracans, branchiosaurid amphibians, tetrapod footprints and tetrapod body fossils within the biochronological framework of land-vertebrate faunachrons. Correlation to the Standard Global Chronostratigraphic Scale presented here is divided into seven time intervals: Pennsylvanian, Carboniferous–Permian boundary, Cisuralian, Guadalupian, Lopingian, Permian–Triassic boundary and Early to Middle Triassic. The insects, conchostracans and branchiosaurs provide robust nonmarine correlations in the Pennsylvanian–Cisuralian, and the footprints and tetrapod body fossils provide robust correlations of varied precision within the entire Pennsylvanian–Middle Triassic. Radioisotopic ages are currently the strongest basis for cross correlation of the nonmarine biostratigraphy/biochronology to the Standard Global Chronostratigraphic Scale, particularly for the Pennsylvanian–Cisuralian. Chemostratigraphy and magnetostratigraphy thus far provide only limited links of nomarine and marine chronologies. Improvements in the nonmarine-marine correlations of late Paleozoic–Triassic Pangea require better alpha taxonomy and stratigraphic precision for the nonmarine fossil record integrated with more reliable radioisotopic ages and more extensive chemostratigraphic and magnetostratigraphic datasets.     

New fish assemblages from the Middle Permian from the Guadalupe Mountains,West Texas,USA

Late Wordian/Capitanian (Guadalupian, Middle Permian) fish assemblages are described from the “McKittrick Canyon Limestone”, Lamar Limestone and Reef Trail Members of the Bell Canyon Formation in the Patterson Hills and the PI section (Hegler/Pinery Members) along Highway 62/180 in the Guadalupe Mountains, West Texas. The assemblages contain chondrichthyan teeth of Stethacanthulus meccaensis, Texasodus varidentatus, Cooleyella cf. amazonensis, C. cf. peculiaris, and the new genus and species Lamarodus triangulus; and buccopharyngeal denticles of undetermined symmoriiform; chondrichthyan scales of eight morphotypes; fragment of an actinopterygian jaw, isolated teeth; the scales of Alilepis sp., Varialepis sp. and undetermined elonichthyid and haplolepid fishes. Using microtomography, the vascularization system has been observed for the first time for the teeth of Texasodus varidentatus and a new taxon Lamarodus triangulus. The distribution of chondrichthyan taxa was analyzed for the known fish assemblages of the Early, Middle, and Late Permian of the world. The end-Guadalupian crisis in the evolution of chondrichthyan fishes involved substantially more taxonomic change than the Permian–Triassic mass extinction.     

Seasonal variation of Sargassum ilicifolium (Phaeophyceae) growth on equatorial coral reefs

Temporal and spatial variations in Sargassum ilicifolium thallus density and length were investigated on equatorial coral reefs in Singapore from November 2011 to October 2012. Thalli density varied little throughout the year, however, we found strong seasonal patterns in thallus length and identified temperature as the significant driver. Sargassum ilicifolium reached maximum length in December (110.39 ± 2.37 cm) during periods of cooler water temperatures, and minimum length in May (9.88 ± 0.48 cm) during periods of warmer water temperatures. Significant spatial variation was also observed for both thallus density and length of S. ilicifolium among reefs. Within reefs, densities of S. ilicifolium were higher on reef flats (20.40 ± 0.40 individuals · 0.25 m^?2) compared to upper reef slopes (5.66 ± 0.23 individuals · 0.25 m^?2). Our findings highlight that marked seasonality in the growth of canopy‐forming macroalgae can occur within equatorial reef systems where temperature ranges are restricted (<3°C).     

Precocious sexual dimorphism and the Lilliput effect in Neo‐Tethyan Ostracoda (Crustacea) through the Permian–Triassic boundary

The Elikah River section spanning the Lopingian (Late Permian) to the Griesbachian (Early Triassic) time interval in the Central Alborz Mountains (north Iran) was sampled for ostracod analysis. We report 79 species distributed among 38 genera. Four new species are described: Acratia? pervagata Forel sp. nov., Microcheilinella alborzella Forel sp. nov., Basslerella superarella Crasquin sp. nov. and Cavellina nesenensis Crasquin sp. nov. The ontogeny of 13 species is described and sexual dimorphism in the genus Microcheilinella is here undoubtedly recognized for the first time. Six species show precocious sexual dimorphism of their carapace as early as A‐5 juvenile. The Lilliput effect is for the first time recorded and quantified for two species. Rare long‐time span Palaeocopida species, known throughout the entire Permian, document relatively long‐term evolution, including the size and growth rate modifications associated with the earlier appearance of carapace sexual dimorphism through time. These patterns might be related to the Guadalupian–Lopingian events and/or to climatic modifications occurring during the Permian interval.     

Oldest scleractinian coral reefs on the North American craton: Upper Triassic (Carnian), northeastern British Columbia,Canada

Bioclastic accumulations composed of crinoids, brachiopods, molluscs, spongiomorphs and scleractinian corals occur within Upper Triassic strata of the lower Baldonnel Formation at Pardonet Hill in northeastern British Columbia Canada. These small buildups (∼100 to 500 m³) have planar bases and broadly convex tops. These mounds are interpreted as small patch reefs composed of packstone, bioclastic floatstone/rudstone and carbonate breccia intercalated with mixed siliciclastic carbonate sediments deposited in a shallow subtidal setting (i.e. above fairweather wave base). Amalgamated hummocky cross-stratified to current ripple-laminated, quartz-dominated sandstone beds and numerous sharp-based, normally graded bioclastic (commonly encrinitic) packstone/grainstone — quartz–sandstone couplets characterize inter-reef lithologies.Conodont biostratigraphy indicates that the Pardonet Hill patch reefs occur within strata dated as earliest Upper Carnian (lower nodosus zone). The Pardonet Hill patch reefs originated and developed during an interval of regional sea level lowstand. Strata within which these patch reefs occur represent the westernmost migration of the Triassic shoreline in western Canada. Disappearance of coral reefs in the study area may have been affected by rapid marine transgression and failure of reef faunas to recolonize the new shore zone further to the east.The Pardonet Hill locality occurred on the western margin of the North American craton during the Triassic. Prior to their discovery reef-like structures dominated by corals in the western Panthalassa were limited to allochthonous terranes (now part of the Cordillera). The Pardonet Hill patch reefs occur at approximately 30° Triassic paleolatitude. In modern settings, this is at the extreme latitudinal margin of subtropical zooxanthellate reef development. The presence of benthic faunas characteristic of low-paleolatitude settings on the northwestern coast of Pangea has significant implications in paleotectonic and paleoenvironmental reconstructions.     

When and how did the terrestrial mid-Permian mass extinction occur? Evidence from the tetrapod record of the Karoo Basin,South Africa

A mid-Permian (Guadalupian epoch) extinction event at approximately 260 Ma has been mooted for two decades. This is based primarily on invertebrate biostratigraphy of Guadalupian–Lopingian marine carbonate platforms in southern China, which are temporally constrained by correlation to the associated Emeishan Large Igneous Province (LIP). Despite attempts to identify a similar biodiversity crisis in the terrestrial realm, the low resolution of mid-Permian tetrapod biostratigraphy and a lack of robust geochronological constraints have until now hampered both the correlation and quantification of terrestrial extinctions. Here we present an extensive compilation of tetrapod-stratigraphic data analysed by the constrained optimization (CONOP) algorithm that reveals a significant extinction event among tetrapods within the lower Beaufort Group of the Karoo Basin, South Africa, in the latest Capitanian. Our fossil dataset reveals a 74–80% loss of generic richness between the upper Tapinocephalus Assemblage Zone (AZ) and the mid-Pristerognathus AZ that is temporally constrained by a U–Pb zircon date (CA-TIMS method) of 260.259 ± 0.081 Ma from a tuff near the top of the Tapinocephalus AZ. This strengthens the biochronology of the Permian Beaufort Group and supports the existence of a mid-Permian mass extinction event on land near the end of the Guadalupian. Our results permit a temporal association between the extinction of dinocephalian therapsids and the LIP volcanism at Emeishan, as well as the marine end-Guadalupian extinctions.     

前乐平统海洋动物灾变事件

作为古生代最后阶段的乐平统可划分为２个阶和４个亚阶,暂以逼近自然界线的Ｃｌａｒｋｉｎａ ｐｏｓｔｂｉｔｔｅｒｉ带之底为下界;在二叠纪形成了栖霞期之前和吴家坪期之前两个超序界面,乐平世海侵居于二叠一三叠纪超序的低水位体系,乐平世末的海泛淹没了古特提斯区的残留陆棚;二叠纪末的生物大绝灭形成规模和性质不同的两幕;茅口期末全球性海退使栖居地丧失而导致地方性类群和远洋浮游生物灭亡的前乐平统海泮动物灾变事件,