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Endocranial anatomy and phylogenetic position of the crocodylian Eosuchus lerichei from the late Paleocene of northwestern Europe and potential adaptations for transoceanic dispersal in gavialoids
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Eosuchus lerichei is a gavialoid crocodylian from late Paleocene marine deposits of northwestern Europe, known from a skull and lower jaws, as well as postcrania. Its sister taxon relationship with the approximately contemporaneous species Eosuchus minor from the east coast of the USA has been explained through transoceanic dispersal, indicating a capability for salt excretion that is absent in extant gavialoids. However, there is currently no anatomical evidence to support marine adaptation in extinct gavialoids. Furthermore, the placement of Eosuchus within Gavialoidea is labile, with some analyses supporting affinities with the Late Cretaceous to early Paleogene “thoracosaurs.” Here we present novel data on the internal and external anatomy of the skull of E. lerichei that enables a revised diagnosis, with 6 autapormorphies identified for the genus and 10 features that enable differentiation of the species from Eosuchus minor. Our phylogenetic analyses recover Eosuchus as an early diverging gavialid gavialoid that is not part of the “thoracosaur” group. In addition to thickened semi-circular canal walls of the endosseous labyrinth and paratympanic sinus reduction, we identify potential osteological correlates for salt glands in the internal surface of the prefrontal and lacrimal bones of E. lerichei. These salt glands potentially provide anatomical evidence for the capability of transoceanic dispersal within Eosuchus, and we also identify them in the Late Cretaceous “thoracosaur” Portugalosuchus. Given that the earliest diverging and stratigraphically oldest gavialoids either have evidence for a nasal salt gland and/or have been recovered from marine deposits, this suggests the capacity for salt excretion might be ancestral for Gavialoidea. Mapping osteological and geological evidence for marine adaptation onto a phylogeny indicates that there was probably more than one independent loss/reduction in the capacity for salt excretion in gavialoids.
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RBINS Staff Publications 2025
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Clumped isotope thermometry (Δ47) measurements in marine gastropods suggest equilibrium precipitation
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The clumped isotope paleothermometer (Δ47) has been used to reconstruct temperatures from various biogenic carbonate archives. Calibration studies demonstrate that some biogenic carbonates precipitate in Δ47 equilibrium and record growth temperatures accurately (e.g., many bivalve mollusks), while others appear to exhibit disequilibrium, or ‘vital’, effects and yield isotopically reconstructed temperatures that are biased (e.g., shallow-water corals). These studies have largely excluded marine gastropods, so it is not known whether they tend to precipitate their shells in or out of isotopic equilibrium. In this study, we present seasonal-scale δ18O and seasonally targeted Δ47 and Δ48 measurements from modern marine gastropods representing 8 genera and 10 species, reconstructing apparent growth temperatures and screening for equilibrium precipitation. We find that most marine gastropods appear to precipitate in Δ47 and Δ48 equilibrium and faithfully record environmental temperatures, making them suitable for Δ47-paleothermometry. A few gastropods (Caviturritella/Turritella sp., Campanile symbolicum, Megastraea undosa) appear to precipitate out of Δ47 equilibrium, though these disequilibrium signatures may partially be explained by differences between actual growth temperatures and instrumental calibration temperatures (Caviturritella/Turritella sp., M. undosa) or differences between inner and outer layer precipitation (C. symbolicum). We present new Δ47-temperature data for 2 Middle Eocene Campanile giganteum fossils collected from the Paris Basin and discuss how to interpret the results in the context of our modern samples. Finally, in conducting this calibration we demonstrate paired Δ47/Δ48 as an effective tool to screen for disequilibrium precipitation in marine gastropods.
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RBINS Staff Publications 2025 OA
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A European monsoon-like climate in a warmhouse world
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The middle Eocene warmhouse period (45 million years ago) featured atmospheric carbon dioxide concentrations equivalent to those projected under high future emission scenarios. Seasonal- to weather timescale climate reconstructions from this period can provide critical insight into the impact of Anthropogenic warming on intra-annual variability in temperature and precipitation. Here, we combine daily-scale reconstructions of the evolution of temperature and the water cycle in western Europe based on stable oxygen and clumped isotope analyses on the fastest-growing gastropod known in the fossil record: Campanile giganteum. Our dataset shows that the middle Eocene of western Europe featured monsoon-like conditions, with seawater temperatures of ˊ24 °C during mild and wet winters, 30 °C during hot and dry spring and autumn seasons, and ˊ28 °C during warm and comparatively wet summers. Coupled climate model simulations using the Community Earth System Model indicate these seasonal variations in temperature and precipitation were driven by shifting atmospheric and oceanic circulation regimes over Western Europe, with winds from different directions bringing distinct waters to the region and minimal wind during spring reducing cooling through diminished latent heat flux. Our results highlight that Europe may experience wetter summers with more frequent extreme rainfall events under future high emissions scenarios.
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RBINS Staff Publications 2025 OA
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Flint formation and astronomical pacing in the Maastrichtian chalk of northwestern Europe
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In Upper Cretaceous chalk sequences, the widespread occurrence of flint, as well as a possible astronomical pacing of their often-encountered rhythmic distribution, remains poorly constrained. The Campanian-Maastrichtian Hallembaye chalk succession (Maastrichtian type area, northeast Belgium) is characterized by the gradual evolution from no flint bands at its base to the regular presence of well-developed flint bands at its top. Here, the Hallembaye section is investigated to gain more insights into the underlying processes behind flint inception. A relationship is found between the amount of detrital material (i.e., clays) present in the chalk and flints, and the extent of silicification and flint development. Several astronomical cycles are identified within the succession using both a lithology-based flint proxy and high-resolution μXRF-based element data from chalk samples. A combined imprint of precession and obliquity is documented in the chalk Ti/Al profile. The flint bands display a predominant obliquity imprint with an increasing contribution of precession and eccentricity up-section. Two consistent stratigraphically integrated astronomical age models are preferred. The first model is a floating age model that is based on the minimal tuning of the short obliquity cycle in the Ti/Al signal. The second model is a numerical age model that is based on flint occurrences, tuned to a combined tuning target consisting of both the inclination and long eccentricity metronomes. Temporal variations in the hydrological cycle and consequent changes in eolian, fluvial and dissolved Si input to the European Basin appear astronomically controlled. In addition, flint nodules and bands are paced by Milankovitch timescales, reflecting astronomical control on the Si cycle and paleoenvironmental conditions governing conditions favorable towards flint formation.
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Deep marine records of Deccan Trap volcanism before the Cretaceous–Paleogene (K–Pg) mass extinction
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The Cretaceous–Paleogene boundary is marked by a large impact and coeval mass extinction event that occurred 66 m.y. ago. Contemporaneous emplacement of the volcanic Deccan Traps also affected global climate before, during, and after the mass extinction. Many questions remain about the timing and eruption rates of Deccan volcanism, its precise forcing of climatic changes, and its signature in the marine geochemical sedimentary proxy record. Here, we compile new and existing mercury (Hg) concentration and osmium isotope (187Os/188Os) records for various stratigraphic sections worldwide. Both geochemical proxies have been suggested to reflect past variations in Deccan volcanic activity. New data from deep marine pelagic carbonate records are compared to contemporaneous records from shallower marine sites correlated through high-resolution cyclostratigraphic age models. The robustness of the proxy records is evaluated on a common timeline and compared to two different Deccan eruption history scenarios. Results show that the global 187Os/188Os signal is clearly reproducible, while the global Hg record does not form a consistent pattern. Moreover, the deep marine sections investigated do not record clear variations in the Hg cycle, particularly in the latest Cretaceous, prior to the extinction event. A detailed reevaluation of the precise depth of the redistribution of impactor-sourced platinum group elements does not exclude the possibility of a minor drop in 187Os/188Os corresponding with a pulse of Deccan volcanism ˊ50,000 years before the Cretaceous–Paleogene boundary. Simple Os isotope mass balance modeling indicates that the latest Cretaceous was marked by significant levels of basalt weathering. CO2 sequestration during this weathering likely overwhelmed the emission of Deccan volatiles, thereby contributing to the end of the late Maastrichtian warming.
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Making sense of variation in sclerochronological stable isotope profiles of mollusks and fish otoliths from the early Eocene southern North Sea Basin
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Stable isotope sclerochemistry of biogenic carbonate is frequently used for the reconstruction of paleotemperature and seasonality. Yet, few studies have compared intra-and inter-taxon isotope variability and variation within a single depositional environment. We measured seasonal changes in δ18O and δ13C compositions in multiple specimens of two carditid bivalve species, a turritelline gastropod species, and two species of otoliths from demersal fish, from two early Eocene (latest Ypresian, 49.2 Ma) coquinas in the inner neritic Aalter Formation, located in the Belgian part of the southern North Sea Basin (paleolatitude ∼41°N). Results demonstrate considerable variation among taxa in the mean, amplitude, and skewness of δ18O and δ13C values from sequentially sampled growth series. We attribute this variation to factors including differences in seasonal growth over ontogeny, mixing of depositional settings by sediment transport, differences between sedentary and mobile organisms, and differences in longevity of the taxa in question. Growth cessation during winters in turritellines and fishes in particular lead to an incomplete representation of the seasonal cycle in their growth increments, in comparison to carditid bivalves. Ophidiid fish otolith isotope records appear to reflect environmental conditions over a wider range of habitats and environments, and we infer this is due to a combination of sedimentary transport, as these are small structures, and postmortem transport by free-swimming predatory fish. Our study highlights the potential variability encompassed by taxa in the shallow marine realm even when they are found in the same deposits. While this has significant implications for seasonality reconstructions based on conventional isotope profiles, we show that careful study of the ecology and ontogeny of multiple taxa and specimens within a death assemblage can reveal sources of variation and yield a close approximation of conditions in the setting of interest.
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Reduced contribution of sulfur to the mass extinction associated with the Chicxulub impact event
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The Chicxulub asteroid impact event at the Cretaceous-Paleogene (K-Pg) boundary ˊ66 Myr ago is widely considered responsible for the mass extinction event leading to the demise of the non-avian dinosaurs. Short-term cooling due to massive release of climate-active agents is hypothesized to have been crucial, with S-bearing gases originating from the target rock vaporization considered an important driving force. Yet, the magnitude of the S release remains poorly constrained. Here we empirically estimate the amount of impact-released S relying on the concentration of S and its isotopic composition within the impact structure and a set of terrestrial K-Pg boundary ejecta sites. The average value of 67 ± 39 Gt obtained is ˊ5-fold lower than previous numerical estimates. The lower mass of S-released may indicate a less prominent role for S emission leading to a milder impact winter with key implications for species survival during the first years following the impact.
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RBINS Staff Publications 2025 OA
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Niche partitioning in the odontocete fauna from the Early Miocene Chilcatay Formation of Peru
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RAPTORS AS A RESOURCE: NEW INSIGHTS INTO MIDDLE AND UPPER PALEOLITHIC BIRD USE AT WALOU CAVE (BELGIUM) BY NEANDERTHALS AND MODERN HUMANS
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On the presence of Calliostoma inopinatum Dautzenberg, 1911 (Gastropoda: Calliostomatidae) off the south coast of Crete (Greece)
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