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The Carnian Pluvial Event (CPE) was an interval marked by global climatic and environmental change, along with biotic turnover, which occurred during the early Late Triassic. Although the causes and consequences of this event remain unclear, one possible scenario is enhanced volcanism injecting greenhouse gases into the atmosphere, perturbing the global carbon cycle, and negatively impacting the global environment. However, there is an underlying challenge in showing a true cause- and-effect relationship between volcanism and the CPE, as both the sedimentary and volcanic records are difficult to date accurately enough to demonstrate temporal correspondence. However, mercury (Hg) can be used to fingerprint catastrophic volcanism in the sedimentary record. We examined two sections that record the CPE at Laishike and Wayao in Guizhou Province, southwest China, which display high Hg contents along with spikes of Hg/total organic content (TOC), Hg/Al, Hg/total sulfur (TS), and Hg/(Mo/Al) during the CPE that indicate a shift to excess Hg loading. These Hg anomalies are correlative with the global negative excursion in δ13Ccarb values at the CPE, which suggests that increased volcanism injected both massive amounts of Hg and isotopically light carbon into the atmosphere, and these were ultimately recorded in marine sediments. This interpretation is supported by slightly negative or near-zero Δ199Hg values that are consistent with a volcanic Hg source. Our study supports the hypothesis that enhanced volcanism played a major role in the evolution of biota and the environment during the CPE.

The Rhynchonellida is a major group of brachiopods that survived the “big five” mass extinctions and flourished after the Permian/Triassic (P/Tr) crisis. However, phylogenetic and character evolution in the Rhynchonellida across the P/Tr transition is poorly understood. In view of the widespread homoplasy across this order, we employ a tip-dated Bayesian analysis to reconstruct phylogenetic relationships for late Permian–Triassic rhynchonellides. The same data were also analyzed using three other methods: undated Bayesian, equal-weighting, and implied-weighting parsimony. Compared with trees generated by other methods, those constructed by tip-dating best account for the homoplasy in this group and are closer to previous assumptions on the evolution of this order. Based on the analyses of multiple trees, the major increase in lineage richness occurred in the Early and early Middle Triassic. Also, richness in the Anisian almost reached the highest level seen in the Triassic. According to fossil records, a pronounced reduction in shell size and in the development of ornamentation occurred after the P/Tr extinction, which is largely due to the loss of large and highly sculptured genera and the diversification of small-sized and weakly ornamented genera. Ancestral-state estimation of shell size and development of ornamentation, coupled with comparisons of other characters, indicate that the Early–Middle Triassic mature “small-sized taxa” may have characters displayed by juveniles of their ancestors. This suggests that for these genera, paedomorphosis was possibly a strategy to survive and diversify in the harsh environment after the P/Tr extinction.

The Permian-Triassic mass extinction severely depleted biodiversity, primarily observed in the body fossil of well-skeletonized animals. Understanding how whole ecosystems were affected and rebuilt following the crisis requires evidence from both skeletonized and soft-bodied animals; the best comprehensive information on soft-bodied animals comes from ichnofossils. We analyzed abundant trace fossils from 26 sections across the Permian-Triassic boundary in China and report key metrics of ichnodiversity, ichnodisparity, ecospace utilization, and ecosystem engineering. We find that infaunal ecologic structure was well established in the early Smithian. Decoupling of diversity between deposit feeders and suspension feeders in carbonate ramp-platform settings implies that an effect of trophic group amensalism could have delayed the recovery of nonmotile, suspension-feeding epifauna in the Early Triassic. This differential reaction of infaunal ecosystems to variable environmental controls thus played a substantial but heretofore little appreciated evolutionary and ecologic role in the overall recovery in the hot Early Triassic ocean.

The Earth has been beset by many crises during its history, and yet comparing the ecological impacts of these mass extinctions has been difficult. Key questions concern the kinds of species that go extinct and survive, how communities rebuild in the post-extinction recovery phase, and especially how the scaling of events affects these processes. Here, we explore ecological impacts of terrestrial and freshwater ecosystems in three mass extinctions through the mid-Phanerozoic, a span of 121 million years (295–174 Ma). This critical duration encompasses the largest mass extinction of all time, the Permian–Triassic (P–Tr) and is flanked by two smaller crises, the Guadalupian–Lopingian (G–L) and Triassic–Jurassic (T–J) mass extinctions. Palaeocommunity dynamics modelling of 14 terrestrial and freshwater communities through a long sedimentary succession from the lower Permian to the lower Jurassic in northern Xinjiang, northwest China, shows that the P–Tr mass extinction differed from the other two in two ways: (i) ecological recovery from this extinction was prolonged and the three post-extinction communities in the Early Triassic showed low stability and highly variable and unpredictable responses to perturbation primarily following the huge losses of species, guilds and trophic space; and (ii) the G–L and T–J extinctions were each preceded by low-stability communities, but post-extinction recovery was rapid. Our results confirm the uniqueness of the P–Tr mass extinction and shed light on the trophic structure and ecological dynamics of terrestrial and freshwater ecosystems across the three mid-Phanerozoic extinctions, and how complex communities respond to environmental stress and how communities recovered after the crisis. Comparisons with the coeval communities from the Karoo Basin, South Africa show that geographically and compositionally different communities of terrestrial ecosystems were affected in much the same way by the P–Tr extinction.

Figure S1. Palaeogeography of Xinjiang and stratigraphy of the studied formations; Figure S2. Nonmetric multidimensional scaling ordinations of food-web; Figure S3. Rarefaction analysis of number of species against number of guilds; Figure S4. Diversity versus duration of time bin plot of the palaeocommunities in Xinjiang; Figure S5. Boxplots showing the variation range in PC1 and PC2 for species-level networks for each community. Community robustness decreases with elevating PC scores for both components; Figure S6-19. Plots showing secondary extinction versus primary perturbation for each of the 14 communities. Period of community is indicated by color, with red for Permian, purple for Triassic and blue for Jurassic; Figure S20-32. Plots showing secondary extinction versus primary perturbation for each of the 13 communities (randomly reduced species richness to 54). Period of community is indicated by color, with red for Permian, purple for Triassic and blue for Jurassic; Table S4. Mann-Whitney U tests results of the collapse thresholds between the original and the reduced species richness communities; Section S1. Sampling and uneven strata issues; Section S2. Principal components analysis (PCA); Section S3. Sources used to compile the database.

The Guryul Ravine section in Kashmir, northern India is an important reference section for global Lower Triassic stratigraphy. Once a candidate Global Stratotype Section and Point (GSSP) for the Permian-Triassic Boundary (PTB), the section has attracted intense attention for the PTB beds, but few studies have concerned the entire Lower Triassic stratigraphy. As one of the most continuous marine Lower Triassic successions on the northern margins of Gondwana, the Guryul Ravine section provides an important conodont biostratigraphic yardstick for worldwide correlations. This study presents recent results of the Lower Triassic conodont zonation from the Guryul Ravine section. A total of 6500 elements including 1600 P1 elements were recovered. Ten conodont zones were recognized from the Griesbachian to Spathian: Hindeodus parvus, Isarcicella staeschei, Clarkina planata, Neoclarkina krystyni, Neospathodus dieneri, Ns. pakistanensis, Novispathodus waageni, Scythogondolella mosheri, Nv. pingdingshanensis, and Nv. abruptus – Nv. brevissimus zones. The PTB is placed within Bed 52 in Unit E2, 80 cm above the base of Unit E2, based on the first occurrence (FO) of H. parvus. The Induan–Olenekian boundary (IOB) is tentatively placed at the base of Member G according to the positive maximum δ13Ccarb values, but it could be slightly higher based on conodonts. The Smithian-Spathian boundary (SSB) is drawn at the top of Member H based on the FO of Nv. pingdingshanensis and the carbon mdpt(N3-P3). Several conodont taxa are newly recognized near the top of the study section where the conodont fauna is dominated by segminiplanate elements of the Neogondolellinae. Many of these age-diagnostic species have been identified in other sections around the world, and their occurrence in Guryul Ravine supports their potential for worldwide correlation. The conodont sequence erected from the study section corresponds well to those of South China (e.g. Meishan) and elsewhere worldwide. The newly established conodont zonation from Kashmir provides a high precision time-frame to consider biotic evolution and environmental change during the Early Triassic, a crucial period of Earth history.

Abundant, exceptionally preserved coprolites are documented from the Luoping biota (Anisian, Middle Triassic) of Yunnan Province, southwest China. These coprolites can be categorized into four morphological types: A) bead to ribbon-shaped, B) short to long cylindrical-shaped, C) flattened, disk-like, and D) segmented faeces. Detailed multi-disciplinary studies reveal that coprolite type A was likely produced by invertebrate animals, while coprolite types B to D could be faeces generated by carnivorous fishes or marine reptiles, perhaps from different taxonomic groups. When compared with coprolites reported from the Lower Triassic, the Luoping forms indicate more complicated predation-prey food web networks. These evidences, combined with body fossil discoveries from Luoping, suggest the emergence of complex trophic ecosystems in the Anisian, marking the full biotic recovery following the Permian–Triassic Mass Extinction.

As the higher trophic guilds in marine food chains, top predators such as larger fishes and reptiles are important indicators that a marine ecosystem has recovered following a crisis. Early Triassic marine fishes and reptiles therefore are key proxies in reconstructing the ecosystem recovery process after the end-Permian mass extinction. In South China, the Early Triassic Jurong fish fauna is the earliest marine vertebrate assemblage in the recovery period. It is constrained as mid-late Smithian in age based on both conodont biostratigraphy and carbon isotopic correlations. The Jurong fishes are all preserved in calcareous nodules embedded in black shale of the Lower Triassic Lower Qinglong Formation, and the fauna comprises at least three genera of Paraseminotidae and Perleididae. The phosphatic fish bodies often show exceptionally preserved interior structures, including network structures of possible organ walls and cartilages. Microanalysis reveals the well-preserved micro-structures (i.e. collagen layers) of teleost scales and fish fins. Abundant small pyrite framboids, 2–5 μm in diameter, are detected from the nodules and fish body surfaces, indicating a calm, euxinic burial environment. Coccoid-like microspheroids are also very abundant in the host rocks and near the fish fossil surfaces, implying that microbes may have participated in the burial process of the fishes. Taphonomic analysis uncovers the four-step formation process of the fish nodules. (1) Fishes lived in the oxic seawater in the upper ocean, and (2) their bodies sank to the anoxic seabed after death, with the body surface being wrapped by bacteria. (3) Microbial biofilms sealed body surfaces to prevent or delay the decay of the fleshy body. The decomposition of the body cavity and interior organs produced some CO2 and H2S gases. The former formed bicarbonate ions in seawater and attracted calcium ions to facilitate the precipitation of calcium carbonate, while the H2S combined with iron ions in seawater to form pyrite framboids. (4) The fish nodule gradually grew by precipitation of calcium carbonate in layers and embedding with pyrite framboids, and later the fish fossil nodule was compacted during diagenesis. Global faunal correlations indicate that the Jurong fishes are closely related to the Early Triassic fish faunas from Chaohu, Anhui Province and Madagascar.

A detailed, 10 m.y. redox history of Changhsingian to Anisian (latest Permian to Middle Triassic) oceans in ramp settings is reconstructed based on framboidal pyrite analysis from South China. The result shows that the well-established phenomenon of intense ocean euxinia-anoxia is faithfully recorded in pyrite framboid data. Three major euxinia-anoxia episodes, namely, the end-Changhsingian to end-Smithian, middle to late Spathian, and early to middle Anisian, have been recognized from the ramp successions. The first reducing episode is subdivided into four subepisodes: Permian-Triassic boundary, Griesbachian-Dienerian boundary, earliest Smithian, and end-Smithian. Redox variations broadly track other oceanographic proxies. Euxinia-anoxia episodes coincide with positive excursions of conodont ΩCe anomalies, negative excursions of δ34Scas (carbonate-associated sulfate), increases in sea-surface temperature, and negative excursions of δ13C in most cases. However, euxinia-anoxia near the Dienerian-Smithian boundary coincided with positive excursions of δ13C and a general cooling period. This exception may be the result of locally developed water-column anoxia. The Permian-Triassic boundary subepisode witnessed two ephemeral euxinia-anoxia events separated by a dysoxic to oxic period. The former, together with a rapid increase in sea-surface temperature (up to 8 °C), may have been responsible for the biodiversity crisis, while the latter anoxic event destroyed ecosystem trophic structures. In addition to the Permian-Triassic boundary euxinia-anoxia event, which spread over habitats in all oceans, the Spathian and Anisian euxinia-anoxia episodes also prevailed in global oceans. Variation of the oxygen minimum zone are suggested as the driving mechanism that facilitated the movement of oxygen-poor water columns in various paleogeographic settings over this critical period.

The Meishan section, South China is the Global Stratotype Section and Point (GSSP) for the Permian-Triassic boundary (PTB), and is also well known for the best record demonstrating the Permian-Triassic mass extinction (PTME) all over the world. This section has also been studied using multidisciplinary approaches to reveal the possible causes for the greatest Phanerozoic biocrisis of life on Earth; many important scenarios interpreting the great dying have been proposed on the basis of data from Meishan. Nevertheless, debates on biotic extinction patterns and possible killers still continue. This paper reviews all fossil and sedimentary records from the Permo-Triassic (P-Tr) transition, based on previously published data and our newly obtained data from Meishan, and assesses ecologically the PTME and its aftermath to determine the biotic response to climatic and environmental extremes associated with the biocrisis. Eight updated conodont zones: Clarkina yini, Clarkina meishanensis, Hindeodus changxingensis, Clarkina taylorae, Hindeodus parvus, Isarcicella staeschei, Isarcicella isarcica, and Clarkina planata zones are proposed for the PTB beds at Meishan. Major turnover in fossil fragment contents and ichnodiversity occurs across the boundary between Bed 24e-5 and Bed 24e-6, suggesting an extinction horizon in a thin stratigraphic interval. The irregular surface in the middle of Bed 27 is re-interpreted as a firmground of Glossifungites ichnofacies rather than the previously proposed submarine dissolution surface or hardground surface. Both fossil fragment contents and ichnodiversity underwent dramatic declines in Beds 25-26a, coinciding with metazoan mass extinction. Fossil fragment content, ichnodiversity and all ichnofabric proxies (including burrow size, tiering level, bioturbation level) indicate that the P-Tr ecologic crisis comprises two discrete stages, coinciding with the first and second phases of the PTME in Meishan. Ecologic crisis lagged behind biodiversity decline during the PTME. Pyrite framboid size variations suggest that depositional redox condition was anoxic to euxinic in the latest Changhsingian, became euxinic in Beds 25-26a, turned dysoxic in Bed 27, then varied from euxinic to anoxic through most of the Griesbachian. The ~9°C increase in seawater surface temperature from Bed 24e to Bed 27 at Meishan seems to result in dramatic declines in biodiversity and fossil fragment contents in Beds 25-26a, but had little effect on all ecologic proxies. Both metazoans and infauna seem not to have been affected by the pre-extinction anoxic-euxinic condition. The anoxic event associated with the PTME may have occurred in a much shorter period than previously thought and is only recorded in Beds 25-26a at Meishan. Fossil fragment contents, ichnofaunas, ichnofabrics and pyrite framboid size all show that no signs of oceanic acidification and anoxia existed in Bed 27. The early Griesbachian anoxia may have resulted in rarity of ichnofauna and metazoans in the lower Yinkeng Formation, in which the ichnofauna is characterized by small, simple horizontal burrows of Planolites, and metazoan faunas are characterized by low diversity, high abundance, opportunist-dominated communities. The rapid increase of ~9°C in sea-surface temperature and a short anoxia or acidification coincided with the first-pulse biocrisis, while a prolonged and widespread anoxia probably due to a long period of high seawater temperate condition may be crucial in mortality of most organisms in the second-pulse PTME. Marine ecosystems started to recover, coupled with environmental amelioration, in the late Griesbachian.

Early Middle Triassic stromatolites are documented for the first time from the Guanling Formation of the Luoping area, eastern Yunnan Province, SW China. The Luoping stromatolites show six types of constructional microbial forms: ?1) typical stratified columnar structures with crinkled laminae. Dark colored laminae are composed of filamentous cyanobacteria, showing a vertical growth fabric. ?2) Laminoid fenestrae and ?3) clotted structures are also commonly present; these clotted fabrics also show an interweaved pattern of ?4) prostrate filaments, which are reflected by strong fluorescence in sharp contrast to dolomite cement in fluorescent images. ?5) Rod-like aggregates, filled with minute dolomite rhombs, are very common in laminae; they resemble present-day cyanobacterial trichome, and thus may represent fossilized cyanobacteria. ?6) Moreover, small pits, coccoid spheroids, calcified biofilms, and fibrous structures are also common in stromatolite laminae. The last two may represent calcified extra-cellular polymer secretions (EPS) that contribute to the development and lithification of stromatolites. Authigenic quartz grains are also common and may have involved biological processes in their formation. These six functional-groups driving accretion and lithification processes of stromatolite documented in literature, both the lithified cyanobacteria/oxygenic phototrophs and sulphate-reducing bacteria (SRB) which induced microbial formation of dolomite are evident in the Luoping stromatolites, suggestive of biogenic origin. The Luoping stromatolites differ from the Early Triassic counterparts in having a great amount of biomass in filamentous cyanobacteria and SRB, whereas both anoxygenic phototrophic bacteria and SRB characterize the Early Triassic stromatolites. Abundant filamentous cyanobacteria may indicate proliferation of oxygenic phototrophs in a normal, oxic habitat. However, abundant SRB indicate sulfate reduction in a stressed habitat. Accordingly, the Luoping stromatolites, coupled with coeval unusual biosedimentary structures, indicate that the post-extinction devastated oceanic conditions may not only have prevailed in the Early Triassic but also have extended to the early Anisian (Middle Triassic) in South China, just before the full recovery of marine ecosystems in middle-late Anisian. 111 Program of China (B08030 to SCX); National Natural 460 Science Foundation grant (No 41272023 to ZQC); grant-in-aid for the study on the 10 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 Permian−Triassic mass extinction and recovery from the State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences (to ZQC).