Following the largest known Phanerozoic extinction, the end-Permian mass extinction, the Early Triassic is often considered an interval of slow biotic recovery. During this time, the minor Smithian-Spathian extinction occurred, further delaying the biotic recovery of this epoch. One mechanism linked to the slow recovery is widespread marine anoxic conditions, but the spatiotemporal changes to anoxia following the mass extinction remain poorly constrained. Here, we utilized local and global redox-sensitive metal proxies to track variations in (de-)oxygenation at Wallenbergfjellet, a section in Spitsbergen, Arctic Norway. Local proxies (e.g., Fe speciation and trace metal concentrations) indicate basinal anoxia and possibly euxinia prevalent in the Boreal Ocean during this interval. Importantly, thallium isotopes, a global paleoredox proxy sensitive to Mn oxide burial, have not previously been applied to the Early Triassic recovery interval that followed the end-Permian mass extinction, though basinal restriction may limit geographic extent of interpretations. Our results show a shift in ε205Tl values from ~ -4.0 in the Smithian to ~ -2.0 at the Smithian-Spathian boundary (SSB), consistent with a rapid expansion of global anoxia coincident with the boundary extinction. A rapid perturbation in thallium isotopes at the SSB (from -4.0 to -2.0 ε-units) indicates this interval experienced an expansion of anoxic conditions that can be linked to the minor extinction event during the recovery interval following the end-Permian mass extinction. This suggests that global anoxia persisted throughout the Early Triassic and contributed to delayed biotic recovery, with the SSB representing a major intensification of reducing conditions.

Lower Triassic deposits of the Vikingh & oslash;gda Formation on Spitsbergen yield diverse assemblages of chondrichthyans, actinopterygians, coelacanths, lungfish, temnospondyls, and marine reptiles. These fossils mainly occur in three stratigraphic levels spanning the middle Smithian to upper Spathian, documenting key stages of marine vertebrate recovery similar to 2-4 million years after the end-Permian mass extinction (EPME). In 2015-2016, similar to 36 m(2) of the lower Spathian Grippia Bonebed was excavated, yielding thousands of isolated skeletal elements within a dense multi-taxic Konzentrat-Lagerst & auml;tte. Here, we present a taphonomic analysis of the Grippia Bonebed to reconstruct the processes of its formation and assess potential taphonomic biases. The deposit is a clast-supported conglomerate composed of bones and coprolites within silty shale facies representing a distal shelf palaeoenvironment. Skeletal elements show varying post-mortem transport alterations, with a low to moderate degree of abrasion. The assemblage formed via hydrodynamic concentration, possibly by storm-driven deposition. The high density of fossils and minimal sediment volume suggest condensation of the accumulated elements, while suboxic to anoxic conditions and phosphatisation enhanced preservation potential. Taphonomic and sampling biases impact taxonomic representation, particularly at lower trophic levels. These are manifested by dissolution of invertebrates and underrepresentation of some vertebrate groups, particularly actinopterygians, due to selective preservation of poorly diagnostic elements. Consequently, this study is the first documentation of a Lower Triassic marine bonebed formed in a distal shelf setting and one of the oldest phosphate clast accumulations following the EPME, offering new insights into early Mesozoic ecosystems and refining a framework for global comparisons of similar deposits.

The geologically oldest sea-going reptile fossils occur in Lower Triassic (Smithian, ca. 250 Ma) strata of the Lusitaniadalen Member ([LM], Vikingh & oslash;gda Formation) on the Norwegian Arctic island of Spitsbergen. Yet some recent studies have dismissed this biostratigraphically and chemostratigraphically demonstrated record with a counterclaim that fully pelagic reptiles must have originated up to similar to 1 m.y. later (mid-Spathian, ca. 248.7 +/- 1.0 Ma) because of radiometric dating on a deposit in China. Here, we resolve this contention using a comprehensive suite of stratigraphic, isotopic, elemental, and petrographic analyses that unanimously age-correlate the LM marine reptile fossils with the middle-to-upper Smithian Euflemingites romunduri-Wasatchites tardus ammonoid zones. These underlie a stratigraphic hiatus preceding the Smithian-Spathian boundary (ca. 249.236 Ma). The LM fossil-bearing layers do not extend down-sequence beyond the Dienerian-Smithian boundary (ca. 250.626 Ma). Thus, the oldest-known oceanic reptile remains are unambiguously constrained at ca. 1.24-2.63 Ma after the cataclysmic end-Permian mass extinction (ca. 251.867 Ma).

Trace fossils, microbially induced sedimentary structures (MISS), palynomorphs and particulate organic matter (POM) found in post-impact sediments in the Gardnos meteorite crater provide evidence of reestablishment of a Neoproterozoic ecosystem in a shallow marine, littoral environment, with sediments covered by microbial mats. Trace fossils are rare and restricted to horizontal burrows, including Gordia, Helminthopsis, Yichnia and poorly preserved tracks resembling Archaeonassa. MISS and water-escape structures are common and include characteristic features like Aristophycus. The recovered organic walled microfossils Trachysphaeridium laminaritum and Sphaerocongregus variabilis indicate a late Neoproterozoic age for the post-impact sediments. Particulate organic matter in deposits comprise dominantly dark grey to black, highly thermally altered amorphous kerogen and fragments of algal material (TAI similar to 4, temperature > 250 degrees C). The trace fossils and MISS are typical of Neoproterozoic shallow marine mat-ground environments which existed prior to the development of Phanerozoic mixed-ground ecosystems.

The marine Grippia bonebed from Vikinghøgda Formation, Lower Triassic, Svalbard is composed of scattered skeletal remains, teeth and coprolites. From this, five coprolite morphotypes have been identified and described. In this study 97 coprolites were examined and classified based on their morphology and inclusions. Thin sections, scanning electron microscope (SEM) and micro-computed tomography (micro-CT) were used to analyze the inclusions revealing skeletal material, fish scales and notably the first observations of invertebrates in this locality. Among the invertebrate components were sponge spicules, a fragment of a cephalopod shell and numerous onychites. Potential coprolite producers are evaluated and likely include chondrichthyans, osteichthyes, ichthyopterygians and temnospondyls. Additionally, this research provides a CT-scanning method for identifying low-density inclusions such as onychites and contribute to a better understanding of the marine Early Triassic paleoecosystem and food web on Svalbard.

The nasal cavities of mammals contain the maxilloturbinate bones, which are involved in reducing heat and water losses. The maxilloturbinates of Arctic seals develop into particularly elaborate labyrinthine patterns, which are well adapted to retain heat and moisture from exhaled gas. These structures develop prenatally and continue to grow postnatally. The developmental mechanism of labyrinthine patterning is unknown. Here we report a model of maxilloturbinate pattern formation in prenatal and juvenile seals based on a simple algorithmic description and three key parameters: target turbinate porosity, characteristic ossification time scale, and typical gestation time scale. Under a small set of geometrical and physical rules, our model reproduces key features of the patterns observed in the turbinate structure of three seal species. To validate our model, we measure complexity, hydraulic diameter, backbone fractal dimension, and Horton-Strahler statistics for a rigorous quantitative comparison with actual tomograms of grey and harp seal skull specimens. Our model closely replicates the structural development of seal turbinates in these respects. Labyrinthine maxilloturbinate development may depend on the ability for neighbouring bone branches to detect and avoid each other, potentially through the mechanosensing of shear stresses from amniotic fluid and air flow.

Tetrapods invaded oceanic environments after the cataclysmic end-Permian mass extinction (EPME), with temnospondyl amphibian to reptile-dominated assemblages succeeding across the Early Triassic [~251.9 to 247.2 million years ago (Ma)]. However, conflicting fossil occurrences, divergence estimates, and stratigraphic time averaging make the tempo of this landmark evolutionary transition uncertain. In this work, we describe an oceanic tetrapod ecosystem from a condensed mid–Early Triassic (early Spathian, ~249 Ma) bone bed on the arctic island of Spitsbergen. Apex predator ichthyosaurians, small-bodied ichthyopterygians, durophagous ichthyosauriforms, semiaquatic archosauromorphs, euryhaline temnospondyls, coelacanths, lungfish, ray-finned fish, and sharks formed an unexpectedly complex trophic network. Comparative diversity analyses further show that heterogeneous marine vertebrate communities were well established by the late-earliest Triassic (Dienerian-Smithian, ~251 Ma) and integrated fully variegate tetrapod niches by ~3 million years after the EPME.

This study presents a detailed analysis of the Middle Triassic Botneheia Formation in Svalbard, integrating sedimentology, geochemistry and palaeontology to understand the depositional environment. Fieldwork was conducted at five localities in central Spitsbergen and Edge & oslash;ya, with two additional localities in western Spitsbergen and Bj & oslash;rn & oslash;ya for comparison. Three carbon-isotope excursions are identified for the first time in the Botneheia Formation in central Spitsbergen and on Edge & oslash;ya- Carbon Excursion (ALICE), and positive Ladinian-Carnian Carbon Isotope Excursion (LICE). It is possible that OACIE is also present in western Spitsbergen and Bj & oslash;rn & oslash;ya and that LICE extends to Bj & oslash;rn & oslash;ya. We discuss their potential use as regional chronostratigraphic markers, drawing global comparisons. Systematic documentation of body and trace fossils from bulk sediment samples reveals benthic fossils in 153 out of 339 samples, and a higher diversity especially of bivalves than previously assumed for the Botneheia Formation. There are notable differences in benthic diversity and oxygenation between central Spitsbergen and Edge & oslash;ya, with lower diversities in the east, associated with more dysoxic conditions. These differences may be linked to the Ural Delta approaching from the east causing algal blooms and haloclines already in the Middle Triassic. The combination of geochemical proxies with fossil assemblages provides a detailed reconstruction of a Boreal Sea seabed during the Middle Triassic and highlights the influence of fluctuating oxygen levels in shaping benthic ecosystems and depositional environments.

The End Permian Mass Extinction (EPME) occurred at 251.9 Ma and is the largest extinction event in the Phanerozoic. More than 80% of marine species and ~75% of terrestrial species were wiped out in

The Lower Cretaceous (Barremian) Kuhnpasset sedimentary sequence of northeast Greenland contains many carbonate deposits in different stratigraphic positions in the area of Wollaston Forland, several of which have previously been identified as having a hydrocarbon seep origin based on their macrofossil content and morphology. Most of the seep carbonates contain complex internal microfabrics, including abundant yellow calcite and banded and botryoidal cement with S13C values as low as-54 %o. These S13C values are characteristic of carbonate microfabrics with biogenic methane as the major carbon source and carbonate authigenesis caused by sulfate-driven anaerobic oxidation of methane (SD-AOM). Such 13C-depletion confirms a methane seep origin of most of the Kuhnpasset carbonate deposits. Molecular fossils from the seep carbonates prove methanotrophic archaea were involved in the SD-AOM consortia, based on 13C-depleted 2,6,10,15,19-pentamethylicosane (PMI; S13C:-122 to-113 %o) and the co-eluting crocetane and phytane (-124 to-105 %o). The carbon source for the Kuhnpasset seeps was biogenic methane with a S13C value of approximately-70 %o, as calculated from compound-specific S13C values of archaeal lipid biomarkers. The S13C values of the biomarkers of sulfate-reducing bacteria, the synthrophic partners of archaea in SD-AOM, including isoand anteiso-C15/17 fatty acids are less 13C-depleted (-107 to-87 %o) than the archaeal biomarkers-a pattern known from modern seep environments. Preservation of bacterial fatty acids is rare for Mesozoic seep deposits, revealing excellent biomarker preservation and low thermal maturity of the Kuhnpasset seep deposits. The common isoprenoid hydrocarbon biomarkers of SD-AOM in the Kuhnpasset seep carbonates are accompanied by 13C-depleted isoprenoic acids (phytanoic acid:-112 to-101 %o); these compounds are attributed to the early degradation of glycerol diether membrane lipids such as archaeol or sn2-hydroxyarchaeol, which are not preserved in the samples. Similarly, regular PMI-acid (-120 to-107 %o) probably represents a derivative of extended archaeol or extended hydroxyarchaeol. The molecular fossil inventories in the Kuhnpasset seep carbonates and the predominance of early diagenetic banded and botryoidal cement are characteristic of the dominance of ANME-2 consortia adapted to high methane flux with the sulfate-methane transition zone (SMTZ) positioned at shallow sediment depth. Abundant wood fragments and well-preserved leafy conifer shoots enclosed in the Kuhnpasset seep deposits indicate a shallow marine paleoenvironment of deposition close to the former shoreline.

[This corrects the article DOI: 10.1371/journal.pone.0280208.].

From the Middle Jurassic to Early Cretaceous, the mudstone-dominated Agardhfjellet Formation was deposited during the prolonged shelf dysoxic-anoxic event (SDAE) recorded predominantly in the circum-arctic polar regions. Commonly, oceanic anoxic events (OAEs) throughout Earth's history are linked to the emplacement of large igneous provinces (LIPs). OAEs and LIPs, alone or jointly, are inferred to be triggers for severe biotic crises in Earth's history. However, the causes for SDAEs remain uncertain. To elucidate these causes, we document the geochemical features of the Agardhfjellet Formation using trace element concentrations and stable isotope ratios. The Agardhfjellet Formation, which consists of the Oppdalen, Lardyfjellet, Oppdalss & aring;ta, and Slottsm & oslash;ya members in ascending order, formed during -13 Myr of prolonged dysoxic, anoxic, and euxinic conditions. The onset of shelf anoxia took place between deposition of the Oppdalen and Lardyfjellet Members. The extent of sea floor anoxia in the basin varied within the Lardyfjellet Member but likely persisted throughout most of the Slottsm & oslash;ya Member. Mo/TOC and Mo EF /U EF ratios in the sedimentary rocks are consistent with the anoxic events. Enhanced continental runoff marked the Oppdalen, Oppdalss & aring;ta, and Slottsm & oslash;ya members, contrasting with most of the Lardyfjellet Member, in which authigenic phases were widespread under anoxic conditions. Our results show that, compared to other OAEs, such as the Toarcian OAE (-183 Ma) or the OAE2 (-94 Ma), the Late Jurassic - Early Cretaceous SDAE recorded in the Agardhfjellet Formation is characterized by prolonged suboxic-anoxic condition, substantial water -mass stratification, and increased continental runoff.

Vertebrate and invertebrate fossils from the Smithian (Early Triassic) to the Early-Middle Triassic boundary interval of Svalbard, Arctic Norway have been known for a long time, but have rarely been extensively collected with precise stratigraphical control. We describe new bulk collections from precisely measured sections in the Vikinghogda Formation in Central Spitsbergen. Accompanying geochemical data provide further constraints on the changes in palaeoenvironments. Species richness of both benthos and nekton remains low throughout the studied interval but reduces to a minimum in the early Spathian, i.e. in the wake of the late Smithian extinction and a probable associated short ice age that straddled the Smithian-Spathian boundary as manifested by a global hiatus in continental shelves. The faunal stratigraphical succession and geochemical data series indicate a regression event in the late Smithian followed by deepening sea level in the early Spathian. This is consistent with a global cooling phase in the late late Smithian that has been previously interpreted as a likely glacio-eustatic episode. The lowermost Spathian is marked by near-absence of benthos, compatible with increased water depth but also possibly linked to the aftermath of the Smithian-Spathian extinction. The lateral expansion of another and younger gap ('the Marmierfjellet hiatus' of early or middle Spathian age) is here interpreted as an off-shore condensation horizon generated by the probably highest sea-level stand recorded in the Spathian of Spitsbergen. These hiatuses of opposite origin, as well as the acute selective preservation linked with the low carbonate content of the studied series, have to be factored out as biases when estimating species richness and interpreting palaeo-ecological changes. The study also identifies Early Triassic fossil taxa new to Spitsbergen, in particular Peribositria sibirica and bakevellid bivalves. The orthoceratoids are reviewed, and two distinct taxa are identified at different stratigraphical levels.

The Early Triassic Smithian and Spathian time intervals are characterized by perturbations in the global carbon cycle, fluctuations in sea surface temperature, high turnover rates of marine nekton, and a change in terrestrial vegetation. Despite the importance of this time interval, comprehensive multiproxy investigations from Early Triassic high and middle latitude regions remain scarce due to the difficulty in accessing sections. The objective of this study is to increase our understanding of regional and local palaeoenvironmental and carbon cycle perturbations from a middle Smithian to late Spathian middle latitude section from Central Spitsbergen. Geochemical analyses show an increase in phosphorus and nitrogen just at and above the Smithian-Spathian boundary (SSB). High primary productivity led to increasingly anoxic conditions in bottom waters during the middle and late Spathian, enhancing the preservation of organic matter in the sediments. Anoxic conditions restrain phosphorus remineralization, allowing it to be recycled within the water column. This increase in anoxia is consistent with observations in other Arctic basins, demonstrating larger regional similarities in palaeoenvironmental conditions. The fluctuations in isostatic and eustatic sea levels affected organic carbon sequestration by regulating organic matter mineral interactions via the control of grain size within the sediment. This study demonstrates that local organic carbon sequestration in the Barents Sea shelf during the Spathian was influenced by a multitude of factors, including sedimentology, redox conditions, nutrient availability, and primary productivity. square Vikingh & oslash;gda Formation, bulk rock geochemistry, particulate organic matter, extinction recovery, carbon isotopes, Stensi & ouml;fjellet

Ammonite provincialism makes it difficult to link the Boreal and Tethyan realms during the Late Jurassic to Early Cretaceous time. Absolute ages through radiometric dating offer new age information that is independent and complementary to relative ages based on biostratigraphy. In this study, we report seven new Re-Os ages for black shales from the Agardhfjellet Formation, Svalbard. We also report pyrolysis results, carbon and sulfur stable isotopic data, and initial 187Os/188Os ratios to evaluate the paleoenvironment during organic-rich shale deposition. Re-Os ages are derived from three Boreal ammonite zones: (1) 159.2 and 160.1 Ma from the shale intervals containing Cadoceras sp.; (2) 149.6, 149.9, 150.8, and 151.9 Ma from the Rasenia cymodoce Zone in the Early Kimmeridgian, which is the equivalent of the Sutneria platynota and Ataxioceras hypselocyclum zones in the Tethyan realm; (3) 146.8 Ma from an upper Volgian interval above the occurrence of Laugeites sp.. Within this 14.5 Myr interval, the initial Os profile shows a gradually increasing trend from 0.335 (one of the lowest shale values throughout the Phanerozoic) to 0.529, consistent with previous initial Os studies and Sr isotopic ratio chemostratigraphic studies. The trend of increasing initial Os ratios indicates an increase in continental runoff relative to unradiogenic Os input from mantle sources, such as seafloor hydrothermal activity or ultramafic source rocks. We provide new Re-Os geochronological anchors in the Late Jurassic with new Re-Os ages and propose correlations of specific Late Jurassic ammonite zones between the Tethyan and Boreal realms. In turn, the gradual increase in seawater Os isotopic ratios may signal climate change in the Late Jurassic, indicating the increase of radiogenic Os or decrease of unradiogenic Os, induced by high continental runoff or less hydrothermal/volcanic activity.

The Smithian-Spathian transition (similar to 249.2 Ma) is marked by profound environmental changes, carbon cycle perturbations, and the stepwise loss of nektonic biodiversity (ammonoids and conodonts). While biotic and abiotic changes have been intensely studied for the palaeosubtropics and palaeotropics, the global spatio-temporal pattern, including mid- to higher latitudes, remains unresolved. In this study, we present conodont and palynomorph data from the Lower Triassic Vikinghogda Formation in the Stensiofjellet section, Svalbard. Conodont samples from this sequence generally yielded relatively few specimens with one exception in the basal Vendomdalen Member, which proved exceptionally abundant and diverse. Most conodont samples of the Lusitaniadalen Member are typically dominated by middle to late Smithian segminiplanate forms, such as Scythogondolella spp. This exceptional horizon in the basal Vendomdalen Member, associated with the cosmopolitan ammonoid Bajarunia, indicates an earliest Spathian age. This sample presents the first-ever recorded conodont fauna from the earliest Spathian in the Boreal realm and associates segminiplanate with numerous segminate forms. The presence of an abundant and diverse segminate conodont fauna in northern mid-latitudes during the Early Triassic suggests that temperature was not the main regulator for their distribution, as opposed to segminiplanate forms, which were apparently more restricted to colder waters. Palynomorphs are poorly preserved but allow the discrimination of three assemblages. Association 1 is lycophyte spore dominated, and associations 2 and 3 are both dominated by bisaccate pollen. The change from lycophyte-dominated to a gymnosperm-dominated vegetation occurs just above the Wasatchites beds. A comparison with the records from the southern palaeosubtropics indicates that the vegetation shift was synchronous and coincided with the onset of a cooling episode, commencing in the latest Smithian.

The black shales of the Middle Triassic Botneheia Formation in Svalbard are known for their fossil richness with abundant ichthyosaur remains and beds of the bivalve Daonella. Vertebrate remains from the Muen Mountain on Edgeøya are shown to have exceptional X-ray contrast due to a combination of sulphide and sulphate permineralisation and pseudomorphing. Radiography imaging of a previously described specimen, PMO 219.250, revealed new and spectacular details such as more carpals, teeth, and skull sutures. Teeth and skull characters are taxonomically significant. supporting the referral of PMO 219.250 to Phalarodon and further suggesting an affinity to P. atavus. Three sulphur phases were identified, with the sulphide sphalerite (ZnS) being the highest temperature phase, followed by the sulphate baryte (BaSO4), and the sulphide pyrite (FeS2). Sulphate permineralisation is also seen in specimens from the Upper Jurassic on Svalbard. We suggest that sulphur-rich fluids have flowed and dissolved barium from the shales and deposited the sphalerite and baryte, and that this could be linked to the Cretaceous HALIP. The Jurassic specimens are only permineralised by baryte, while the Triassic specimens have also been permineralised, but mainly pseudomorphed by baryte with crystals of sphalerite. Lithology differences appear to have controlled the compaction of the Triassic specimens, while the Jurassic specimens have retained their three-dimensional shape due to the baryte emplacement relatively earlier in their depositional history. Although soft tissues are not preserved, the excellent X-ray contrast in the Middle Triassic specimens is reminiscent of pyritised fossil sites such as the Hunsrück Slate (Devonian), Beecher's Trilobite Bed (Ordovician), and the La Voulte-sur-Rhône marls (Jurassic).

Pseudoplankton are organisms that are adapted for a mode of life attached to floating objects.In modern oceans common examples are lepadid barnacles, which attach themselves to man-made and natural objects, especially wood logs.In the fossil record, pseudoplankton examples are commonly found in black shales, such as the lower Toarcian Posidonia Shale Formation of Germany.Here there are occasional large logs of fossil wood covered in specimens of the inoceramid bivalve Pseudomytiloides dubius, with or without specimens of the pentacrinitid crinoid Seirocrinus subangularis.Some Posidonia Shale logs show evidence of for intra-species succession with younger S. subangularis specimens attached onto the stems of older ones.Another example of pseudoplankton from the Posidonia Shale is the occurrence of the numerous disarticulated specimens of the phosphatic-shelled eolepadid barnacle Toarcolepas mutans associated with a piece of fossil wood, which constitutes the oldest example of pseudoplanktonic barnacles in the fossil record.Here we report a limestone concretion from the lower Toarcian Strawberry Bank Lagerstätte (Ilminster, Somerset, UK) that preserves a piece of fossil wood with a pseudoplanktonic colony comprising at least a hundred specimens of T. mutans that attached onto a layer of P. dubius bivalves, that had already attached onto the wood.This is one of very few examples of temporal succession for pseudoplankton in the Toarcian and is also unusual in being preserved in a mixed carbonate-siliciclastic facies, rather than a black shale.The occurrence of T. mutans in the Strawberry Bank Lagerstätte concretion represents the second record of the species and also the equal oldest example of pseudoplanktonic barnacles in the fossil record.

The Middle Devonian (Givetian) Valentia Slate Formation in the Iveragh Peninsula, southwest Ireland, is more renowned for the second oldest record of tetrapod trackways in the world than for its heavily metamorphosed bone remains. The present study focuses on new discoveries of non-tetrapod sarcopterygian fish fossils from the Valentia Slate Formation. Micro-CT scanning technology allows a re-interpretation of a previously published acanthodian fin spine as a fanged coronoid of a probable Rhizodontida and the identification of a Dipnoi tooth plate and bone. In addition, a scale of Holoptychius is described. The presence the rhizodont suggests Gondwanan ties and a first northward dispersal wave of these vertebrates into Euramerica as early as middle Givetian. This hypothesis is supported by the common occurrence of the placoderm Bothriolepis in the Valentia Slate Formation.