A new oryctocephalid trilobite from the Balang Formation (Cambrian Stage 4) of northwestern Hunan,South China,with remarks on the classification of oryctocephalids

A new trilobite, Longaspis paiwuensis n. gen. n. sp., from the Balang Formation (Cambrian Stage 4) in northwestern Hunan, South China, is described. This rare trilobite adds to an expanding taxonomic list of organisms recognized from the Balang Lagerstätte, a deposit of exceptional preservation from the Cambrian. Longaspis paiwuensis is an unusually large-sized, micropygous oryctocephalid trilobite that has proparian facial sutures, pit-like lateral glabellar furrows, up to 17 thoracic segments, and a distinct medial notch in the pygidium; it lacks marginal spines.The classification of the family Oryctocephalidae is reviewed. Three subfamilies are recognized, and Longaspis n. gen. is assigned to the subfamily Oryctocarinae.     

Unique lowermost Cambrian small shelly fossils (SSFs) from eastern Yunnan,South China: implications for the early diversification history of animals

With a particular focus on the earliest Cambrian diversification of small shelly fossils (SSFs), stratigraphic analysis was conducted on the lower Cambrian Zhongyicun Member at the Hongjiachong section in the Chengjiang area, Yunnan, China. From ca. 3-m-thick bedded phosphorites (Unit A) in the lower part of the member, we recovered unique SSFs. This interval with 4 SSF-bearing horizons is characterized by the dominance in blade-shaped SSFs, including Halkieria spp., Brushenodus prionodes, Sinosachites delicatus, and Pteronus sp., and the absence of typical tube/cap-shape SSFs common in the Fortunian. This interval tentatively named “Halkieria-dominant interval” is stratigraphically positioned ca. 3 m below the previously known level of the oldest mollusks in the continuous bedded phosphorite sequence between the Anabarites trisulcatus-Protohertzina anabarica Assemblage Zone and the overlying Paragloborilus subglobosa-Purella squamulosa Assemblage Zone of the Fortunian (the earliest Cambrian). The “Halkieria-dominant interval” yields some SSFs likely affiliated with ostracods in view of size and morphology, suggesting that arthropod body fossils appeared in the Fortunian, considerably earlier than previously believed.     

End-Permian mass extinction of calcareous algae and microproblematica from Liangfengya,South China

A new assemblage of calcareous algae and microproblematica is reported from the Changxing Formation at the Liangfengya section in Chongqing, South China. This assemblage comprises eighteen species of seven genera, including three genera of gymnocodiaceaens (Gymnocodium, Permocalculus, and Tauridium), three genera of dasycladaleans (Epimastopora, Macroporella, and Mizzia), and one genus of microproblematica (Pseudovermiporella). A new algal species, Tauridium elongatum nov. sp., is described. Quantitative analysis indicates that the last occurrences of 22% of the species (4 out of 18) fall into a 52 cm thick interval of the uppermost Changhsingian. No calcareous algae are found in the Permian-Triassic boundary (P-T boundary) beds and the overlying Feixianguan Formation. Four out of 10 species have a stratigraphic abundance greater than 10% and all vanished in the uppermost Changhsingian. An abrupt extinction for calcareous algae occurred in the Clarkina yini conodont Zone.     

Potential global stratotype sections and points in China for defining Cambrian stages and series

Three stratigraphic sections in the Cambrian of China that contain complete successions across important biohorizons having chronostratigraphic value, and that may be useful for developing Cambrian stage or series boundaries, are reviewed. The Wuliu section (Guizhou, South China), contains the FAD of Oryctocephalus indicus at 58.2 m above the base of the Kaili Formation. The Wangcun North section (Hunan, South China), contains the FADs of Ptychagnostus (or Acidusus) atavus, Ptychagnostus punctuosus, and Lejopyge laevigata at 1.2 m, 56.7 m, and 111.3 m, respectively, above the base of the Huaqiao Formation. The Xiaoyangqiao section (Jilin, Northeast China), contains the FAD of Cordylodus proavus in the Fengshan Formation at 10.89 m above the zero point of the section. A fourth potential stratotype section, the Wangcun South section (Hunan, South China), which contains the P. atavus, P. punctuosus, and L. laevigata zones, is discussed briefly.     

Reassessment of the mode of life of Pagetia Walcott, 1916 (Trilobita: Eodiscidae) based on a cluster of intact exuviae from the Kaili Formation (Cambrian) of Guizhou, China

Pagetia is the most abundant trilobite in the Kaili Formation (lower to middle Cambrian). During the course of studying the museum collections of Kaili trilobites ( n  > 1000), a cluster containing 22 pagetiid individuals at various growth stages is noted. Specimens record the growth range from the degree 0 meraspid to late holaspid phases. Based on the relative completeness of the moults except for missing free cheeks, these specimens are interpreted as intact exuviae that had undergone minimal transport prior to burial. If Kaili pagetiids had pelagic or planktonic living habits as previously suggested, it would be difficult to explain the presence of intact exuviae in clusters. Therefore, Kaili pagetiids are interpreted here as having a benthic mode of life after the onset of the meraspid phase.     

Late ontogeny of the trilobite Tsinania shanxiensis (Zhang and Wang, 1985) from the Cambrian (Furongian) of Anhui,China and its systematic implications

A new occurrence of Tsinania shanxiensis (Zhang and Wang, 1985) n. comb., is reported herein from northern Anhui, China. This species is here transferred from Guluheia to Tsinania as the differences between the two genera are not enough to support the generic difference. The late ontogeny of T. shanxiensis is documented herein, which provides important evidence for the evolutionary origin of the Family Tsinaniidae. The late ontogeny of the pygidia of T. shanxiensis is divided into four stages: PSS+2 stage, PSS+1 stage, early holaspid stage, and late holaspid stage. The immature morphology of T. shanxiensis retains long pygidial spines, reminicent of Mansuyia. Therefore, the morphology of T. shanxiensis can be regarded as the transitional type between kaolishaniids (e.g., Mansuyia orientalis, M. tani) and tsinaniids (e.g., T. canens, Shergoldia laevigata) during the middle Furongian.     

Oikozetetes from the early Cambrian of South Australia: implications for halkieriid affinities and functional morphology

Shells of Oikozetetes and isolated halkieriid sclerites from a section of the lower Cambrian Mernmerna Formation in the Flinders Ranges, South Australia, are tentatively considered as being derived from the same scleritome. Details of shell morphology and the possible combination of biomineralized shell and sclerites suggest that Oikozetetes , if interpreted correctly, is closely related to Halkieria . A new interpretation of Oikozetetes shell morphology, in addition to the first report of paired muscle scars on the interior surface, sheds new light on the possible functional morphology of halkieriid shells and the means of attaching the shell to the body. The occurrence of Oikozetetes in South Australia extends its biostratigraphic range to the lower Cambrian and biogeographic range to East Gondwana.     

The Frasnian-Famennian mass extinction: insights from high-resolution sequence stratigraphy and cyclostratigraphy in South China

Two sequences (SFr, SFa), each 1-1.2 Myr in duration, are recognised in the strata across the Frasnian-Famennian (F-F) transition both in carbonate platform and interplatform basinal successions in South China. The sequence boundary between the two sequences is placed a little below the top of the Frasnian. The sequences are basically composed of coarsening-upward/bed-thickness increasing-upward cycles and shallowing-upward cycles (parasequences) in basinal and platform deposits respectively, which stack into cycle-sets (typically six to eight cycles). 10 and 12 cycle-sets are identified in sequences SFr and SFa respectively. These cycle-sets can be further grouped into larger-scale composite cycle-sets (herein termed mesocycle- and megacycle-sets with two and four cycle-sets respectively). This vertical cycle-stacking pattern and the hierarchy of cyclicity suggest a Milankovitch style of forcing such that the cycles and cycle-sets were formed in response to the orbital perturbations of precession (16-18 kyr) and eccentricity (∼100 kyr in duration), respectively. In the basinal cycles, smaller-scale rhythmic stratification beds (typically six to eight beds in a cycle) are extensive, and were likely caused by millennial-scale climatic forcing. In the lower sequence, SFr, the latest highstand deposits consist of calciturbidites and debrites in deep-water strata and fenestral limestones in shallow-water strata, representing a major (third-order) sea-level fall. Within these deposits, four cycle-sets are further identified in both coeval deep-water and platform successions. Succeeding deeper-water organic-rich facies, within which three cycles occur, are the transgressive deposits of the overlying Famennian sequence (SFa). These cycles represent three higher-frequency (16-18 kyr) sea-level fluctuations and accompanying anoxia, superimposed on a major third-order sea-level rise. The F-F boundary is placed at the top of the first cycle, based on conodont data. Thus, a major sea-level fall and then a rise occurred in the F-F transitional period. Faunal and sedimentological data reveal a massive biotic decline in concert with the major sea-level fall, and a further biotic demise coinciding with the major sea-level rise and its three superimposed higher-frequency sea-level fluctuations and accompanying anoxia. The F-F biotic crisis was therefore characterised by two episodes of step-down extinction. On the basis of Milankovitch orbital rhythms, the first major biotic extinction took place over ∼400 kyr, and the subsequent event was ∼50 kyr in duration, i.e. ∼450 kyr for the entire event. At the same time as the massive decline of normal-marine fossils during the latest Frasnian sea-level fall, there was widespread cyanobacterial growth and a thriving of planktonic calcispheres, suggesting eutrophic conditions. This situation could have caused a severe biotic loss, as a result of the deterioration of surface water clarity and formation of anoxic bottom waters due to over-consumption of oxygen through respiratory demands and decomposition by the cyanobacteria and phytoplankton. The subsequent rapid sea-level rise with superimposed higher-frequency sea-level fluctuations and accompanying anoxia could have caused rapid elevation of anoxic bottom waters and expansion of eutrophic surface waters over shallow-water platforms due to enhanced upwelling ocean currents and improved ocean circulation. This situation would have exerted further stresses upon the already-weakened biota, leading to a further biotic demise. However, a small number of organisms such as pelagic tentaculitids, small mud-adapted brachiopods and gastropods did survive into the Famennian, although with very low diversity.     

Paleoecological patterns in molluscan extinctions and recoveries: comparison of the Cretaceous-Paleogene and Eocene-Oligocene extinctions in North America

Exposures across the Cretaceous-Tertiary (K-T) and Eocene-Oligocene (E-O) boundaries, in Texas and Mississippi, respectively, probably represent the most complete and best-preserved fossil molluscan sequences across these boundary intervals in the world. Outcrops from both boundaries contain pristine aragonitic and calcitic molluscan shells, which were deposited in fine-grained sediments from open marine environments. The K-T and the E-O extinctions exhibit very different recovery patterns, probably reflecting very different causes as well as magnitudes of extinction.The K-T sequence contains a molluscan fossil record that is consistent with an abrupt extinction event at the K-T boundary and a prolonged initial recovery in hostile oceanographic conditions. The uppermost 10 m of Upper Cretaceous sediments contain a diverse (approximately 40 species) molluscan fauna dominated by suspension feeders. The earliest Paleocene sediments immediately above the tsunami bed contain an impoverished fauna dominated by deposit feeders. The Paleocene fauna slowly climbs in diversity but remains relatively impoverished and dominated by deposit feeders for several hundred thousand years after the extinction in conjunction with anomalous δ¹³C values that suggest prolonged suppression of marine primary productivity. Diverse suspension-feeder dominated molluscan assemblages reappear with the resumption of normal conditions of primary production. In the long term, early to middle Paleocene gamma diversity includes evolutionary “bloom taxa,” families that exhibit unusual speciation bursts that subside in the Eocene. Total diversity for the Gulf Coast does not approach Cretaceous levels until the Late Eocene representing a total recovery interval of nearly 25 million years.While the E-O event also reflects a molluscan extinction rate of over 90% in the Gulf of Mexico, there are no signs of hostile environmental conditions in the recovery fauna. Early Oligocene molluscan assemblages are diverse and dominated by suspension feeders characteristic of normal marine conditions. The hiatus at the E-O boundary, however, could have obscured a short-term recovery fauna. There is also no sign of long-term perturbation by the E-O extinction. There are no bloom taxa and gamma diversity approaches pre-extinction levels within a few million years. The overall pattern of the E-O extinction is consistent with extinction (and/or migration) associated with long-term cooling.     

Paleogeographic variations of pedogenic carbonate delta13C values from Koobi Fora, Kenya: implications for floral compositions of Plio-Pleistocene hominin environments

Plio-Pleistocene East African grassland expansion and faunal macroevolution, including that of our own lineage, are attributed to global climate change. To further understand environmental factors of early hominin evolution, we reconstruct the paleogeographic distribution of vegetation (C(3)-C(4) pathways) by stable carbon isotope (delta(13)C) analysis of pedogenic carbonates from the Plio-Pleistocene Koobi Fora region, northeast Lake Turkana Basin, Kenya. We analyzed 202 nodules (530 measurements) from ten paleontological/archaeological collecting areas spanning environments over a 50-km(2) area. We compared results across subregions in evolving fluviolacustrine depositional environments in the Koobi Fora Formation from 2.0-1.5 Ma, a stratigraphic interval that temporally brackets grassland ascendancy in East Africa. Significant differences in delta(13)C values between subregions are explained by paleogeographic controls on floral composition and distribution. Our results indicate grassland expansion between 2.0 and 1.75 Ma, coincident with major shifts in basin-wide sedimentation and hydrology. Hypotheses may be correct in linking Plio-Pleistocene hominin evolution to environmental changes from global climate; however, based on our results, we interpret complexity from proximate forces that mitigated basin evolution. An approximately 2.5 Ma tectonic event in southern Ethiopia and northern Kenya exerted strong effects on paleography in the Turkana Basin from 2.0-1.5 Ma, contributing to the shift from a closed, lacustrine basin to one dominated by open, fluvial conditions. We propose basin transformation decreased residence time for Omo River water and expanded subaerial floodplain landscapes, ultimately leading to reduced proportions of wooded floras and the establishment of habitats suitable for grassland communities.     

Flume studies using 1:1 scale models of Series 2 and basal Series 3 Cambrian gogiid eocrinoids from Guizhou Province,China to determine feeding posture and mode of attachment

In Series 2 and 3 Cambrian of Guizhou Province, China, most echinoderms inhabited deeper/quieter water and were attached directly to siliciclastic substrate or biodetritus by biogluing (extrusion of extensible collagen). Feeding postures of abundant long stalked gogiids (e.g., Sinoeocrinus) from these beds were interpreted to have heeled over in the current from the thin flexible distal end of the stalk, with the brachioles streaming in a loose bundle, down current from the theca. To test these and other feeding posture assumptions, 1:1 scale models (holdfast, stalk, and theca) of three genera were carved from soft rubber and brachioles were modeled from braided fishing line. By varying current velocities long stalked flume models did not significantly heel over. Brachioles, both straight and spiraled, extended vertically from the theca in an (elliptical) cone and distally curved downstream. Disrupted flow around straight brachioles (Sinoeocrinus) kept them somewhat evenly spaced. Spiraled brachioles (Guizhoueocrinus, Globoeocrinus) are initially straight and angle outwards so that each proximal end defines a sector over the theca; this spacing keeps the brachioles free from tangling distally. Biogluing the animal to the bottom or to biodetritus seems to be correctly interpreted from the morphological evidence. Superglue was used as the proxy gluing agent for the models, success was limited. The dewatered, siliciclastic, non-bioturbated, seafloor could be only partly reconstructed and the somewhat viscous glue did not deeply penetrate the illite substrate. It is probable that bioglue had low viscosity, penetrated the sediment easily, and was able to agglutinate a large three dimensional anchoring body of sediment without (as is commonly observed) disrupting bedding.     

Molluscs,isotopes and ecological fractionation: Examples from the upper Palaeogene of the Hampshire Basin

Carbon and oxygen isotopic analyses from upper Palaeogene molluscs collected in the Hampshire Basin (S. England) show that, in addition to long‐term trends in the data caused by climatic change, there is variation within samples collected from any one horizon. This variation is not attributable to diagenesis or other “noise”;. Linear trends in data from the meso‐ and oligohaline organisms are salinity‐dependent, as is a differentiation into clusters of the marine and brackish water animals. Within the marine organisms there is further distinction between taxa, controlled by micro‐environment. This is quite distinct from disequilibrium precipitation, as shell growth occurs in equilibrium with local isotopic ratios, though this may not necessarily be the same as contemporary mean ocean values. This “ecological fractionation”; can seriously affect the isotopic signal from a suite of fossils. Its existence should therefore be borne in mind when interpreting any biogenic isotope data from diverse taxa, localities, or micro‐habitats.     

Evidence for seafloor microbial mats and associated metazoan lifestyles in Lower Cambrian phosphorites of Southwest China

The increase in the depth and intensity of bioturbation through the Proterozoic-­Phanerozoic transition changed the substrates on which marine benthos lived from being relatively firm with a sharp sediment-water interface to having a high water content and blurry sediment-water interface. Additionally, microbial mats, once dominant on normal marine Proterozoic seafloors, were relegated to stressed settings lacking intense metazoan activity. This change in substrates has been termed the 'agronomic revolution', and its impact on benthic metazoans has been termed the 'Cambrian substrate revolution'. The shallow marine phosphorites of the Lower Cambrian Meishucun Formation of southwest China contain evidence suggestive of the presence of seafloor microbial mats. This evidence includes abundant and distinctive red-colored bedding planes enriched in heavy iron minerals and mica, interpreted as resulting from mat-decay mineralization and mica trapping by microbial mats. The radular grazing trace fossil Radulichnus is also found in this formation, indicating a firm, microbial mat-bound substrate. These radular scratches are always preserved with circular impressions around 10 cm in diameter, possibly the fossils of soft-bodied organisms. The first relatively intense bioturbation in this region is found in this formation and is dominated by horizontal Thalassinoides burrows, which could represent undermat mining behavior. The evidence for the presence of microbial mats in the Lower Cambrian Meishucun Formation, and for metazoan lifestyles associated with such mat-bound seafloors, reveals that normal marine environments dominated by typical Proterozoic-style soft substrates still existed during the Cambrian substrate revolution.     

Potential Global Standard Stratotype-section and Point (GSSP) for a Cambrian stage boundary defined by the first appearance of the trilobite Ptychagnostus atavus, Drum Mountains, Utah, USA

The base of the Ptychagnostus (or Acidusus) atavus Zone is one of the most clearly recognizable horizons on an intercontinental scale in the Cambrian System, and would serve as an excellent position for the base of a new stage-level chronostratigraphic subdivision. Among well-exposed, readily accessible sections in Laurentia, the “Stratotype Ridge” section, Drum Mountains, western Utah, USA, is perhaps the most suitable for a Global Standard Stratotype-section and Point (GSSP) defined by the first appearance datum (FAD) of the cosmopolitan agnostoid trilobite P. atavus. In the “Stratotype Ridge” section, the FAD of P. atavus occurs near the base of a calcisiltite bed 62 m above the base of the Wheeler Formation. A position corresponding closely to this horizon can be recognized with precision in Gondwana, Siberia, Kazakhstan, and Baltica using a combination of stratigraphic tools, the most useful of which are trilobite biostratigraphy, conodont biostratigraphy, and sequence stratigraphy. Brachiopod biostratigraphy and chemostratigraphy provide general constraints on the position of the horizon intercontinentally.     

The gnathobasic spine microstructure of recent and Silurian chelicerates and the Cambrian artiopodan Sidneyia: Functional and evolutionary implications

Gnathobasic spines are located on the protopodal segments of the appendages of various euarthropod taxa, notably chelicerates. Although they are used to crush shells and masticate soft food items, the microstructure of these spines are relatively poorly known in both extant and extinct forms. Here we compare the gnathobasic spine microstructures of the Silurian eurypterid Eurypterus tetragonophthalmus from Estonia and the Cambrian artiopodan Sidneyiainexpectans from Canada with those of the Recent xiphosuran chelicerate Limulus polyphemus to infer potential variations in functional morphology through time. The thickened fibrous exocuticle in L. polyphemus spine tips enables effective prey mastication and shell crushing, while also reducing pressure on nerve endings that fill the spine cavities. The spine cuticle of E. tetragonophthalmus has a laminate structure and lacks the fibrous layers seen in L. polyphemus spines, suggesting that E. tetragonophthalmus may not have been capable of crushing thick shells, but a durophagous habit cannot be precluded. Conversely, the cuticle of S. inexpectans spines has a similar fibrous microstructure to L. polyphemus, suggesting that S. inexpectans was a competent shell crusher. This conclusion is consistent with specimens showing preserved gut contents containing various shelly fragments. The shape and arrangement of the gnathobasic spines is similar for both L. polyphemus and S. inexpectans, with stouter spines in the posterior cephalothoracic or trunk appendages, respectively. This differentiation indicates that crushing occurs posteriorly, while the gnathobases on anterior appendages continue mastication and push food towards and into the mouth. The results of recent phylogenetic analyses that considered both modern and fossil euarthropod clades show that xiphosurans and eurypterids are united as crown-group euchelicerates, with S. inexpectans placed within more basal artiopodan clades. These relationships suggest that gnathobases with thickened fibrous exocuticle, if not homoplasious, may be plesiomorphic for chelicerates and deeper relatives within Arachnomorpha. This study shows that the gnathobasic spine microstructure best adapted for durophagy has remained remarkably constant since the Cambrian.     

Reef reconstruction after extinction events of the latest ordovician in the Yangtze platform,South China

Summary Early Silurian reef reconstruction on the Yangtze Platform, in the northern part of the South China Block, is preceded by a combination of regional and global processes. During most of Ashgill time (Late Ordovician), the area was dominated by Wufeng Formation deep water graptolitic black shales. Reefs largely disappeard in the middle of the Ashgill Stage, from the northwestern margin of Cathaysian Land (southeastern South China Block), in advance of the Late Ordovician glaciation and mass extinction, due to regional sea-level changes and regional uplift, unrelated to the mass extinction itselt. Late Ordovician microbial mudmound occurrence is also found in the western margin of the Yangtze Platform, its age corresponding to theDicellograptus complexus graptolite biozone of pre-extinction time. On the Yangtze Platform, a thin, non-reef-bearing carbonate, the Kuanyinchiao Formation (=Nancheng Formation in some sites), thickness generally no more than 1m, occurs near several landmasses as a result of Hirnantian regression. Reappearance of the earliest Silurian carbonates consisting of rare skeletal lenses in the upper part of Lungmachi Formation, are correlated to theacensus graptolite biozone, early Rhuddanian of Shiqian, northeastern Guizhou, near Qianzhong Land. Carbonate sediments gradually developed into beds rich in brachiopods and crinoids in the lower part of Xiangshuyuan Formation, middle Rhuddanian. In the middle part of Xiangshuyan Formation, biostromes, containing abundant and high diversity benthic faunas such as corals, crinoids and brachiopods, show beginnings of reconstruction of reef facies. Substantial reef recovery occurred in the upper part of Xiangshuyuan Formation, lower Aeronian, as small patch reefs and biostromes. During the late Aeronian, carbonate sediments, especially reefs and reef-related facies, expanded on the upper Yangtze Platform, and radiation of reefs occurred in Ningqiang Formation, upper Telychian. The long period of reef recovery, taking several million years, remains difficult to explain, because redistribution of any refugia faunas would be expected to take place soon after the extinction. Reefs and reef-related facies subsequently declined after Telychian time due to regional uplift of the major portion of the Yangtze Platform. Carbonate facies are therefore uncommon in South China during the rest of Silurian time.     

Trophic structure of macro- and meso-invertebrates in Japanese coniferous forest: Carbon and nitrogen stable isotopes analyses

Few studies have been published on the feeding ecology of Japanese soil fauna based on stable isotope analysis. Therefore, the present work aims to use this technique for studying the trophic structure of Japanese soil fauna at two coniferous forests. Significant differences were observed between investigated sites (Arahama and Gamo) in genus richness and abundance, while for Shannon diversity indexes the difference was non-significant. The isotopic signatures (δ¹³C and δ¹⁵N) of the invertebrates collected at Arahama ranged from 0.3 to 6.3‰ for δ¹⁵N and from −27.3 to −23.3‰ for δ¹³C. At Gamo, invertebrates δ¹³C values ranged from −26.1 to −23.5‰ and δ¹⁵N values ranged from 1.6 to 6.8‰. At both sites, invertebrates formed two distinct groups on the basis of combined C and N stable isotope ratios. The locations of these groups related to δ¹³C values. The less enriched group (δ¹³C < −25‰) and the more enriched one (δ¹³C > −25‰). The range of δ¹⁵N for the present animals exceeded two trophic levels. While, the gradual ¹⁵N enrichment within the invertebrates species may indicate the dominance of omnivory in soil food webs. The differences between sites in δ¹⁵N confirm the importance of studying the trophic structure of soil fauna locally.     

Cerium negative anomaly just before the Permian and Triassic boundary event — The upward expansion of anoxia in the water column

A negative excursion of Ce and a succeeding steep decline in δ¹³C found just before the Permian and Triassic boundary (PTB) of Julfa area offer a geochemical constraint on the cause of the mass extinction event of PTB. The geochemical studies of recent anoxic basins like the Black Sea strongly suggest that the Ce negative excursion of these carbonate platform sequence indicates the buildup of anoxic water in the offshore realm. The suboxic water mass associated with the Ce negative anomaly zone migrated and invaded into shallow carbonate shelf around 600 thousand years before the PTB. This was followed by an anoxic water mass without Ce anomaly, and resulted in a steep decline in δ¹³C and then mass extinction of marine shelf biota.     

Uncertainty in identifying local extinctions: the distribution of missing data and its effects on biodiversity measures

Identifying local extinctions is integral to estimating species richness and geographic range changes and informing extinction risk assessments. However, the species occurrence records underpinning these estimates are frequently compromised by a lack of recorded species absences making it impossible to distinguish between local extinction and lack of survey effort—for a rigorously compiled database of European and Asian Galliformes, approximately 40% of half-degree cells contain records from before but not after 1980. We investigate the distribution of these cells, finding differences between the Palaearctic (forests, low mean human influence index (HII), outside protected areas (PAs)) and Indo-Malaya (grassland, high mean HII, outside PAs). Such cells also occur more in less peaceful countries. We show that different interpretations of these cells can lead to large over/under-estimations of species richness and extent of occurrences, potentially misleading prioritization and extinction risk assessment schemes. To avoid mistakes, local extinctions inferred from sightings records need to account for the history of survey effort in a locality.