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Widespread marine anoxia triggered by the runoff and recycling of nutrients was a key phenomenon associated with the Frasnian–Famennian (FF) mass extinction. However, the relative importance of global‐scale processes versus local influences on site‐specific environmental change remains poorly understood. Here, nitrogen‐isotope (δ15N) trends are combined with organic‐biomarker, phosphorus, and Rock‐Eval data in FF sites from the USA (H‐32 core, Iowa), Poland (Kowala Quarry), and Belgium (Sinsin). Up‐to‐date cyclostratigraphic age models for all three sites allow the nature and timing of changes to be precisely compared across the globe. Negative δ15N excursions across the FF interval from the H‐32 core and Kowala correlate with geochemical evidence for euxinic, phosphorus‐rich, water columns, and possible cyanobacterial activity, suggestive of increased diazotrophic N fixation, potentially coupled with ammonium assimilation at the latter site. By contrast, previously studied sites from Western Canada and South China document enhanced water‐column denitrification around the onset of the Upper Kellwasser (UKW) Event, re‐emphasizing the geographical heterogeneity in environmental perturbations at that time. Moreover, environmental degradation began >100 kyr earlier in Poland, coeval with a major increase in bioavailable phosphorus supply, than in Iowa, where no such influx is recorded. These regional differences in both the timing and nature of marine perturbations during the FF interval likely resulted from the variable influx of terrigenous nutrients to different marine basins at that time, highlighting the importance of local processes such as terrestrial runoff in driving environmental degradation during times of climate cooling such as the UKW Event. Plain Language Summary The Frasnian–Famennian mass extinction, ∼372 million years ago, marked one of the most severe biological crises in Earth's history. The extinction has been linked to rapid climate changes and reduced seawater oxygen levels across the global ocean. However, the degree to which environmental stress was globally versus locally controlled remains unclear. This study presents geochemical markers of water‐column oxygenation and nutrient cycling (nitrogen isotopes, phosphorus contents, organic biomarkers) at three localities, the H‐32 core (Iowa, USA), the Kowala Quarry (Poland), and Sinsin (Belgium). The unique feature of these records is the existence of precise age‐depth models, allowing direct comparison of the timing of environmental changes between these sites, and with other key sections from Western Canada and South China. It is shown that whilst the H‐32 core and Kowala indicate possible increases in cyanobacterial nitrogen fixation under phosphorus‐rich, oxygen‐ and nitrate‐depleted conditions, other sites show markedly different nitrogen‐cycle disturbances, such as enhanced water‐column denitrification. Additionally, environmental stress commenced earlier in Kowala than elsewhere, coincident with elevated phosphorus influx to that setting. These regional variations in the timing and nature of environmental perturbations emphasize the importance of local processes such as terrestrial nutrient runoff in causing the Frasnian–Famennian extinction. Key Points Nitrogen‐isotope records of globally variable environmental change in the Frasnian–Famennian crisis Combination with age models highlights further variability in the onset of those changes Multi‐proxy geochemistry highlights nutrient runoff as trigger of earliest anoxia

Continental interiors were flooded by epeiric seas during many intervals of the geologic past. Few modern analogs exist for these environments, however, and basic variables such as redox, salinity, and restriction are difficult to reconstruct in deep time. Despite these challenges, constraining epeiric watermass properties is critical because much of our preserved and accessible sedimentary record was deposited in such settings. Here, we present a four‐dimensional reconstruction of watermass evolution in the Late Devonian Appalachian Seaway of North America. We use combined proxies for sediment supply, paleosalinity, paleoredox, and basin hydrography in six cores through the Upper Devonian Cleveland Shale deposited across a paleo‐depth transect. Cyclic, coupled changes in sedimentation, redox, and salinity are recorded in environments near the Catskill Delta. Additionally, a pronounced salinity gradient was present from low‐brackish conditions near the delta to fully marine conditions in the basin interior, with a lower‐salinity mixing zone recorded across the Cumberland Sill. We also identified two broad sequences—the lower and upper Cleveland Shale—each of which shows distinct watermass signatures. The lower Cleveland Shale records a redox gradient with euxinia only present along the Cumberland Sill, whereas the upper Cleveland Shale records intensification of euxinia (potentially in the photic zone) at all six sites, which may be coincident with the Hangenberg extinction event. Ultimately, this study identifies pronounced epeiric watermass gradients over short timescales (millennia) and distances (hundreds of km or less), highlighting the need for interpreting the geochemistry of epicontinental deposits in the context of basin hydrography and paleosalinity. Plain Language Summary The interiors of continents were flooded by shallow seas during many intervals of Earth history; however, little is known about the basic watermass properties of ancient inland seas and how they differed from the open ocean. Here, we provide an example of watermass reconstruction in an ancient inland sea by investigating the Cleveland Shale, which was deposited in a flooded region west of the Appalachian Mountains during the Late Devonian (∼383–359 million years ago). We use geochemical proxies for oxygen concentrations (redox) and salinity in six rock cores located across a gradient of ancient water depth. Our data reveal a pronounced salinity gradient and two discrete stages in the sea's chemical evolution, with the first stage recording a strong redox gradient across the sea and the second stage characterized by oxygen deficiency and toxic hydrogen sulfide at all sites investigated. This expansion of shallow‐water hydrogen sulfide occurred at the same time as the Hangenberg mass extinction event that killed many inhabitants of the shallow oceans. Ultimately, this study is among the first to identify pronounced chemical gradients in an ancient inland sea and link spatiotemporal watermass properties to ocean habitability and extinction during a critical time in Earth history. Key Points Four‐dimensional paleoredox, paleosalinity, and hydrographic reconstruction of the Late Devonian Appalachian Seaway Pronounced watermass heterogeneity over short timescales and distances, including large vertical and lateral salinity gradient Basin‐wide intensification of water column (and potentially photic zone) euxinia during the Hangenberg extinction event

An earliest Famennian (Late Devonian) record of tentaculitoids (an extinct 'class' of small calcareous conical shells) preserved as palynomorphs is documented from Sosnogorsk in the Komi Republic of Russia. These were preserved in considerable abundance in a near-shore shallow lagoon subjected to marine flooding with euxinia. Four forms of nowakiid tentaculitoids plus related aberrant forms are documented. They represent evidence for survival of the nowakiids into the earliest Famennian and hence post-date the Frasnian-Famennian mass extinction. It is hypothesised that the Frasnian and younger occurrence of tentaculitoids as palynomorphs may relate to a changing balance of carbonate and organic matter in their shells driven by the environmental conditions of the Frasnian-Famennian mass extinction.

New palynological results from the Gafo Formation (southern sector of the Pulo do Lobo Domain, South Portuguese Zone) are integrated with recently studied sections and drillholes from the Portuguese and Spanish sectors. A total of 44 samples were studied, 27 of which were positive for palynomorph taxonomy. This research revealed well preserved palynological assemblages, including 73 spore species allocated to 28 genera, four acritarch genera, three prasinophyte algae genera plus common chitinozoan remains. Some additional forms were retained under open nomenclature. From this, the first complete age determination for the Gafo Formation in Portugal and Spain was achieved, indicating a middle Famennian (Grandispora gracilis–Grandispora famenensis, GF Biozone) to a late Famennian (Grandispora echinata, VH Biozone) age. A greywacke sample from the same Gafo Formation was dated by U–Pb zircon geochronology and a maximum depositional age of 369 ± 2.5 Ma was obtained. A correlation between these palynological and U–Pb zircon data and the palynoflora assemblages of previous authors was made, as well as with the ages of felsic volcanic rocks found intercalated in the Gafo Formation, confirming the complex stratigraphy of Pulo do Lobo Domain. The results are consistent with stratigraphic mapping and structural interpretations, allowing a middle–late Famennian age (GF and VH Biozone) to be assigned to the Gafo Formation sedimentary rocks. This work has also contributed to a reinterpretation of Gafo Formation depositional facies correlatives (e.g. the Santa Barbara Group in Spain) as being the same lithological unit.

In this study we focused on the dynamics of encrusting assemblages preserved on brachiopod hosts collected from upper Frasnian and lower Famennian deposits of the Central Devonian Field, Russia. Because the encrusted brachiopods come from deposits bracketing the Frasnian/Famennian (F/F) boundary, the results also shed some light on ecological differences in encrusting communities before and after the Frasnian—Famennian (F-F) event. To explore the diversity dynamics of encrusting assemblages, we analyzed more than 1300 brachiopod valves (substrates) from two localities. Taxon accumulation plots and shareholder quorumsubsampling (SQS) routines indicated that a reasonably small sample of brachiopod host valves (n=50) is sufficient to capture themajority of the encrusting genera recorded at a given site. The richness of encrusters per substrate declined simultaneously with the number of encrusting taxa in the lower Famennian, accompanied by a decrease in epibiont abundance, with a comparable decrease in mean encrustation intensity (percentage of bioclasts encrusted by one or more epibionts). Epibiont abundance and occupancy roughlymirror each other. Strikingly, few ecological characteristics are correlated with substrate size, possibly reflecting random settlement of larvae. Evenness, which is negatively correlated with substrate size, shows greater within-stage variability among samples than between Frasnian and Famennian intervals and may indicate the instability of early Famennian biocenoses following the faunal turnover. The occurrence distribution of encrusters points to nonrandomassociations and exclusions among several encrusting taxa. However, abundance and occupancy of microconchids remained relatively stable throughout the sampled time interval. The notable decline in abundance (∼60%) and relatively minor decline in diversity (∼30%) suggest jointly that encrusting communities experienced ecological collapse rather than a major mass extinction event. The differences between the upper Frasnian and lower Famennian encrusting assemblages may thus record a turnover associated with the F-F event.

In 1952, Erik Jarvik diagnosed and offered a brief description of the large-bodied, highly nested tristichopterid taxon Eusthenodon, and its type species E. wangsjoi, from fossils recovered from the Britta Dal Formation (Famennian) of Gauss Halvø ( = Peninsula) and Ymer Ø ( = Island) in East Greenland. The original diagnosis for Eusthenodon only needed to distinguish the tristichopterid taxon from the two others known at the time, Eusthenopteron and Tristichopterus, both of them small-bodied forms with anatomy now recognised to be primitive within the clade. Following that publication, no new large-bodied tristichopterids with Eusthenodon-like characteristics would be introduced until the description of Mandageria fairfaxi in 1997. In the 45 interim years, the limited descriptive details and insufficient diagnosis of Eusthenodon turned the name into a broadly applicable taxonomic label for large-bodied tristichopterid discoveries. Recent efforts to rediagnose the taxon and reconsider its global distribution of referred materials have improved the taxonomic utility of the name. However, no complete description of type species E. wangsjoi has yet been written. This is despite a type series of specimens that includes complete and articulated skulls that remain available for study in the collections of the Natural History Museum of Denmark (NHMD). The work presented here fulfils the need for a complete comparative description of E. wangsjoi in the context of the many highly nested tristichopterid species that have been described in the last three decades. New figures of the E. wangsjoi type series of specimens are the first to offer views of the fossils unobscured by the superimposition of interpretive line drawings. The new description is accompanied by a descriptive inventory of all the potential E. wangsjoi fossils at the NHMD and a new phylogenetic analysis of clade Tristichopteridae that includes revised character data for E. wangsjoi and adds one recently described species.

The Late Devonian ammonoid species Soliclymenia paradoxa (Münster) is recorded for the first time from the Middle Urals, from the Gubakha Formation (Famennian) near the town of Gubakha (Perm Region, Russia). This species was previously known only from Western and Central Europe and South China. It is the first record of a representative of the genus Soliclymenia Schindewolf from the Middle Urals. The history of the study of the genus Soliclymenia and its species is reviewed. The range of the bed with ammonoids is within the Muessenbiaergia parundulata–Effenbergia lens ammonoid zones, correlated with the Upper expansa–Lower praesulcata conodont zones.

The Upper Famennian (Upper Devonian) Strud locality has yielded very abundant and diversified flora as well as vertebrate and arthropod faunas. The arthropod fauna, mostly recovered from fine shales deposited in a calm, confined floodplain habitat including temporary pools, has delivered a putative insect and various crustaceans including eumalacostracans and notostracan, spinicaudatan and anostracan branchiopods. Here we present the Strud eurypterids, consisting of semi-articulated juvenile specimens assigned to Hardieopteridae recovered from the pool and floodplain deposits, as well as larger isolated fragments of potential adults recovered from stratigraphically lower, coarser dark sandy layers indicative of a higher-energy fluvial environment. The Strud fossils strongly suggest that, as proposed for some Carboniferous eurypterids, juvenile freshwater eurypterids inhabited sheltered nursery pools and migrated to higher-energy river systems as they matured.

Phenotypic variation is the raw material of evolution. Standing variation can facilitate response to selection along “lines of least evolutionary resistance”, but selection itself might alter the structure of the variance. Shape was quantified using 2D geometric morphometrics in Palmatolepis conodonts through the Late Devonian period. Patterns of variance were characterized along the record by the variance-covariance matrix (P-matrix) and its first axis (Pmax). The Late Frasnian was marked by environmental oscillations culminating with the Frasnian/Famennian mass extinction. A shape response was associated with these fluctuations, together with a deflection of the Pmax and the P-matrix. Thereafter, along the Famennian, Palmatolepis mean shape shifted from broad elements with a large platform to slender elements devoid of platform. This shift in shape was associated with a reorientation of Pmax and the P-matrix, due to profound changes in the functioning of the elements selecting for new types of variants. Both cases provide empirical evidences that moving adaptive optimum can reorient phenotypic variation, boosting response to environmental changes. On such time scales, the question seems thus not to be whether the P-matrix is stable, but how it is varying in response to changes in selection regimes and shifts in adaptive optimum.

A new cyrtospiriferid species, Cyrtospirifer akimicus sp. nov. is described from the Lower Famennian Pozhnya Formation, which was previously considered as the upper part of Izhma Formation.