René H. B. Fraaije

Earth's climate history serves as a natural laboratory for testing the effect of warm climates on the biosphere. The Cretaceous period featured a prolonged greenhouse climate characterized by higher-than-modern atmospheric CO2 concentrations and mostly ice-free poles. In such a climate, shallow seas in low latitudes probably became very hot, especially during the summers. At the same time, life seems to have thrived there in reef-like ecosystems built by rudists, an extinct group of bivalve molluscs. To test the seasonal temperature variability in this greenhouse period, and whether temperature extremes exceed the maximum tolerable temperatures of modern marine molluscs, we discuss a detailed sclerochronological (incrementally sampled) dataset of seasonal scale variability in shell chemistry from fossil rudist (Torreites sanchezi and Vaccinites vesiculosus) and oyster (Oscillopha figari) shells from the late Campanian (75-million-year-old) low latitude (3° S paleolatitude) Saiwan site in present-day Oman. We combine trace element data and microscopy to screen fossil shells for diagenesis, before sampling well-preserved sections of a Torreites sanchezi rudist specimen for clumped isotope analysis. Based on this specimen alone, we identify a strong seasonal variability in temperature of 19.2 ± 3.8 to 44.2 ± 4.0 °C in the seawater at the Saiwan site. The oxygen isotopic composition of the seawater (δ18Osw) varied from −4.62 ± 0.86 ‰ VSMOW in winter to +0.86 ± 1.6 ‰ VSMOW in summer. We use this information in combination with age modelling to infer temperature seasonality from incrementally sampled oxygen isotope profiles sourced from the literature, sampling multiple shells and species in the assemblage. We find that, on average, the Saiwan seawater experienced strong seasonal fluctuations in monthly temperature (18.7 ± 3.8 to 42.6 ± 4.0 °C seasonal range) and water isotopic composition (−4.33 ± 0.86 to 0.59 ± 1.03 ‰ VSMOW). The latter would strongly bias the interpretation of stable oxygen isotopes in shell carbonate without independent control on either temperature or seawater composition. Combining our seasonal temperature estimates with shell chronologies based on seasonal cyclicity in stable isotope records and daily variability in trace element data, we show that T. sanchezi rudists record temperatures during the hottest periods of the year as well as during the winters, which were characterized by cooler temperatures and enhanced influx of freshwater. Both O. figari and V. vesiculosus plausibly stopped growing during these seasonal extremes. This study aims to demonstrate how high-resolution geochemical records through fossil mollusc shells can shed light on the variability in past warm ecosystems and open the discussion about the limits of life in the shallow marine realm during greenhouse climates. Future work should apply the clumped isotope paleothermometer on incrementally sampled bio-archives to explore the upper-temperature limits experienced by calcifiers in different environments throughout geological history.

Earth’s climate history serves as a natural laboratory for testing the effect of warm climates on the biosphere. The Cretaceous period featured a prolonged greenhouse climate characterized by higher-than-modern atmospheric CO₂ concentrations and mostly ice-free poles. In such a climate, shallow seas in low latitudes probably became very hot, especially during the summers. At the same time, life seems to have thrived there in reef-like ecosystems built by rudists, an extinct group of bivalve molluscs. To test the seasonal temperature variability in this greenhouse period, and whether temperature extremes exceed the maximum tolerable temperatures of modern marine molluscs, we discuss a detailed sclerochronological (incrementally sampled) dataset of seasonal scale variability in shell chemistry from fossil rudist (Torreites sanchezi and Vaccinites vesiculosus) and oyster (Oscillopha figari) shells from the late Campanian (75-million-year-old) low latitude (3° S paleolatitude) Saiwan site in present-day Oman. We combine trace element data and microscopy to screen fossil shells for diagenesis, before sampling well-preserved sections of a Torreites sanchezi rudist specimen for clumped isotope analysis. Based on this specimen alone, we identify a strong seasonal variability in temperature of 19.2 ± 3.8 °C to 44.2 ± 4.0 °C in the seawater at the Saiwan site. The oxygen isotopic composition of the seawater (δ¹⁸O_sw) varied from -4.62 ± 0.86 ‰ VSMOW in winter to +0.86 ± 1.6 ‰ VSMOW in summer. We use this information in combination with age modelling to infer temperature seasonality from incrementally sampled oxygen isotope profiles sourced from the literature, sampling multiple shells and species in the assemblage. We find that, on average, the Saiwan seawater experienced strong seasonal fluctuations in monthly temperature (18.7 ± 3.8 to 42.6 ± 4.0 °C seasonal range) and water isotopic composition (-4.33 ± 0.86 to 0.59 ± 1.03 ‰ VSMOW). The latter would strongly bias the interpretation of stable oxygen isotopes in shell carbonate without independent control on either temperature or seawater composition. Combining our seasonal temperature estimates with shell chronologies based on seasonal cyclicity in stable isotope records and daily variability in trace element data, we show that T. sanchezi rudists record temperatures during the hottest periods of the year as well as during the winters, which were characterized by cooler temperatures and enhanced influx of freshwater. Both O. figari and V. vesiculosus plausibly stopped growing during these seasonal extremes. This study aims to demonstrate how high-resolution geochemical records through fossil mollusc shells can shed light on the variability in past warm ecosystems and open the discussion about the limits of life in the shallow marine realm during greenhouse climates. Future work should apply the clumped isotope paleothermometer on incrementally sampled bio-archives to explore the upper-temperature limits experienced by calcifiers in different environments throughout geological history.

Earth’s climate history serves as a natural laboratory for testing the effect of warm climates on the biosphere. The Cretaceous period featured a prolonged greenhouse climate characterized by higher-than-modern atmospheric CO₂ concentrations and mostly ice-free poles. In such a climate, shallow seas in low latitudes probably became very hot, especially during the summers. At the same time, life seems to have thrived there in reef-like ecosystems built by rudists, an extinct group of bivalve molluscs. To test the seasonal temperature variability in this greenhouse period, and whether temperature extremes exceed the maximum tolerable temperatures of modern marine molluscs, we discuss a detailed sclerochronological (incrementally sampled) dataset of seasonal scale variability in shell chemistry from fossil rudist (Torreites sanchezi and Vaccinites vesiculosus) and oyster (Oscillopha figari) shells from the late Campanian (75-million-year-old) low latitude (3° S paleolatitude) Saiwan site in present-day Oman. We combine trace element data and microscopy to screen fossil shells for diagenesis, before sampling well-preserved sections of a Torreites sanchezi rudist specimen for clumped isotope analysis. Based on this specimen alone, we identify a strong seasonal variability in temperature of 19.2 ± 3.8 °C to 44.2 ± 4.0 °C in the seawater at the Saiwan site. The oxygen isotopic composition of the seawater (δ¹⁸O_sw) varied from -4.62 ± 0.86 ‰ VSMOW in winter to +0.86 ± 1.6 ‰ VSMOW in summer. We use this information in combination with age modelling to infer temperature seasonality from incrementally sampled oxygen isotope profiles sourced from the literature, sampling multiple shells and species in the assemblage. We find that, on average, the Saiwan seawater experienced strong seasonal fluctuations in monthly temperature (18.7 ± 3.8 to 42.6 ± 4.0 °C seasonal range) and water isotopic composition (-4.33 ± 0.86 to 0.59 ± 1.03 ‰ VSMOW). The latter would strongly bias the interpretation of stable oxygen isotopes in shell carbonate without independent control on either temperature or seawater composition. Combining our seasonal temperature estimates with shell chronologies based on seasonal cyclicity in stable isotope records and daily variability in trace element data, we show that T. sanchezi rudists record temperatures during the hottest periods of the year as well as during the winters, which were characterized by cooler temperatures and enhanced influx of freshwater. Both O. figari and V. vesiculosus plausibly stopped growing during these seasonal extremes. This study aims to demonstrate how high-resolution geochemical records through fossil mollusc shells can shed light on the variability in past warm ecosystems and open the discussion about the limits of life in the shallow marine realm during greenhouse climates. Future work should apply the clumped isotope paleothermometer on incrementally sampled bio-archives to explore the upper-temperature limits experienced by calcifiers in different environments throughout geological history.

Although numerous fossils have been excavated and described from the Upper Cretaceous (Maastrichtian) Lance Formation, eggs and eggshell remains are rare and have yet to be described in detail. Here, we provide the first description of an eggshell found in the Lance Formation in eastern Wyoming. The eggshell can be attributed to the oofamily Ovaloolithidae, and is most comparable to the oogenus Ovaloolithus based on the smooth outer surface, the eggshell thickness, the closely packed shell units, and the presence of two layers. The eggshell can tentatively be ascribed to either ornithopod or non-avian theropod dinosaurs. This new eggshell expands our understanding of the geographical distribution of ovaloolithid ootaxa throughout the uppermost Cretaceous of North America, having been previously described from the Maastrichtian North Horn Formation of Utah.

Earth’s climate history serves as a natural laboratory for testing the effect of warm climates on the biosphere. The Cretaceous period featured a prolonged greenhouse climate characterized by higher-than-modern atmospheric CO₂ concentrations and mostly ice-free poles. In such a climate, shallow seas in low latitudes probably became very hot, especially during the summers. At the same time, life seems to have thrived there in reef-like ecosystems built by rudists, an extinct group of bivalve molluscs. To test the seasonal temperature variability in this greenhouse period, and whether temperature extremes exceed the maximum tolerable temperatures of modern marine molluscs, we discuss a detailed sclerochronological (incrementally sampled) dataset of seasonal scale variability in shell chemistry from fossil rudist (Torreites sanchezi and Vaccinites vesiculosus) and oyster (Oscillopha figari) shells from the late Campanian (75-million-year-old) low latitude (3° S paleolatitude) Saiwan site in present-day Oman. We combine trace element data and microscopy to screen fossil shells for diagenesis, before sampling well-preserved sections of a Torreites sanchezi rudist specimen for clumped isotope analysis. Based on this specimen alone, we identify a strong seasonal variability in temperature of 19.2 ± 3.8 °C to 44.2 ± 4.0 °C in the seawater at the Saiwan site. The oxygen isotopic composition of the seawater (δ¹⁸O_sw) varied from -4.62 ± 0.86 ‰ VSMOW in winter to +0.86 ± 1.6 ‰ VSMOW in summer. We use this information in combination with age modelling to infer temperature seasonality from incrementally sampled oxygen isotope profiles sourced from the literature, sampling multiple shells and species in the assemblage. We find that, on average, the Saiwan seawater experienced strong seasonal fluctuations in monthly temperature (18.7 ± 3.8 to 42.6 ± 4.0 °C seasonal range) and water isotopic composition (-4.33 ± 0.86 to 0.59 ± 1.03 ‰ VSMOW). The latter would strongly bias the interpretation of stable oxygen isotopes in shell carbonate without independent control on either temperature or seawater composition. Combining our seasonal temperature estimates with shell chronologies based on seasonal cyclicity in stable isotope records and daily variability in trace element data, we show that T. sanchezi rudists record temperatures during the hottest periods of the year as well as during the winters, which were characterized by cooler temperatures and enhanced influx of freshwater. Both O. figari and V. vesiculosus plausibly stopped growing during these seasonal extremes. This study aims to demonstrate how high-resolution geochemical records through fossil mollusc shells can shed light on the variability in past warm ecosystems and open the discussion about the limits of life in the shallow marine realm during greenhouse climates. Future work should apply the clumped isotope paleothermometer on incrementally sampled bio-archives to explore the upper-temperature limits experienced by calcifiers in different environments throughout geological history.

Earth’s climate history serves as a natural laboratory for testing the effect of warm climates on the biosphere. The Cretaceous period featured a prolonged greenhouse climate characterized by higher-than-modern atmospheric CO₂ concentrations and mostly ice-free poles. In such a climate, shallow seas in low latitudes probably became very hot, especially during the summers. At the same time, life seems to have thrived there in reef-like ecosystems built by rudists, an extinct group of bivalve molluscs. To test the seasonal temperature variability in this greenhouse period, and whether temperature extremes exceed the maximum tolerable temperatures of modern marine molluscs, we discuss a detailed sclerochronological (incrementally sampled) dataset of seasonal scale variability in shell chemistry from fossil rudist (Torreites sanchezi and Vaccinites vesiculosus) and oyster (Oscillopha figari) shells from the late Campanian (75-million-year-old) low latitude (3° S paleolatitude) Saiwan site in present-day Oman. We combine trace element data and microscopy to screen fossil shells for diagenesis, before sampling well-preserved sections of a Torreites sanchezi rudist specimen for clumped isotope analysis. Based on this specimen alone, we identify a strong seasonal variability in temperature of 19.2 ± 3.8 °C to 44.2 ± 4.0 °C in the seawater at the Saiwan site. The oxygen isotopic composition of the seawater (δ¹⁸O_sw) varied from -4.62 ± 0.86 ‰ VSMOW in winter to +0.86 ± 1.6 ‰ VSMOW in summer. We use this information in combination with age modelling to infer temperature seasonality from incrementally sampled oxygen isotope profiles sourced from the literature, sampling multiple shells and species in the assemblage. We find that, on average, the Saiwan seawater experienced strong seasonal fluctuations in monthly temperature (18.7 ± 3.8 to 42.6 ± 4.0 °C seasonal range) and water isotopic composition (-4.33 ± 0.86 to 0.59 ± 1.03 ‰ VSMOW). The latter would strongly bias the interpretation of stable oxygen isotopes in shell carbonate without independent control on either temperature or seawater composition. Combining our seasonal temperature estimates with shell chronologies based on seasonal cyclicity in stable isotope records and daily variability in trace element data, we show that T. sanchezi rudists record temperatures during the hottest periods of the year as well as during the winters, which were characterized by cooler temperatures and enhanced influx of freshwater. Both O. figari and V. vesiculosus plausibly stopped growing during these seasonal extremes. This study aims to demonstrate how high-resolution geochemical records through fossil mollusc shells can shed light on the variability in past warm ecosystems and open the discussion about the limits of life in the shallow marine realm during greenhouse climates. Future work should apply the clumped isotope paleothermometer on incrementally sampled bio-archives to explore the upper-temperature limits experienced by calcifiers in different environments throughout geological history.

A new pylochelid hermit crab, Cretatrizocheles rodfeldmanni new species, is recorded from a Lower Cretaceous (Aptian/Albian) olistolith reefal limestone block near the village of Velika Strmica, southeast Slovenia. It adds to the fossil record of the symmetrical pagurid subfamily Trizochelinae, whose members appear to have been successful inhabitants of shallow-marine reefal settings during at the least the Late Jurassic and Early Cretaceous across Europe. Given their exclusive occurrence in shallow-marine, reef-related facies of Mesozoic age and the present-day confinement to deep-marine settings, trizocheline paguroids may also illustrate the effect of the Mesozoic Marine Revolution.UUID: http://zoobank.org/b3f862ca-3b4d-44c1-911c-820af4426029

Earth’s climate history serves as a natural laboratory for testing the effect of (very) warm climates on the biosphere. The Cretaceous period featured prolonged intervals of greenhouse climates characterized by high atmospheric CO2 concentrations and mostly ice-free poles (O’Brien et al., 2017; Ladant and Donnadieu, 2016). In such a climate, shallow seas in low latitudes likely became very hot, especially during the summer (Jones et al., 2022; de Winter et al., 2021). At the same time, life seems to have thrived there in reef-like ecosystems built by rudists, an extinct group of bivalve mollusks (Gili and Götz, 2018). The summer temperatures documented for these ecosystems exceed the maximum tolerable temperatures of any marine mollusk alive today, which raises the question how these animals adapted to more extreme temperatures.Studying the growth of these ancient organisms and the extreme climate conditions they faced can yield valuable insight into the resilience of marine ecosystems to climate change. To tackle this climate resilience conundrum, we present a detailed sclerochronological (incrementally sampled) dataset of daily to seasonal scale variability in shell chemistry from fossil mollusks from a Campanian (75-million-year-old) low-latitude shallow marine ecosystem. With it, we investigate the extreme climate conditions these animals lived through and how this affected their growth or even the paleo-weather patterns they experienced. The goal of this study is to demonstrate how high-resolution geochemical records through fossil mollusk shells can shed light on the variability in past warm ecosystems and open the discussion about the limits of life in the shallow marine realm during a greenhouse climate. Gili, E. and Götz, S.: Treatise Online no. 103: Part N, Volume 2, Chapter 26B: Paleoecology of rudists, 1, https://doi.org/10.17161/to.v0i0.7183, 2018.Jones, M. M., Petersen, S. V., and Curley, A. N.: A tropically hot mid-Cretaceous North American Western Interior Seaway, Geology, 50, 954–958, https://doi.org/10.1130/G49998.1, 2022.Ladant, J.-B. and Donnadieu, Y.: Palaeogeographic regulation of glacial events during the Cretaceous supergreenhouse, Nat Commun, 7, 12771, https://doi.org/10.1038/ncomms12771, 2016.O’Brien, C. L., Robinson, S. A., Pancost, R. D., Sinninghe Damsté, J. S., Schouten, S., Lunt, D. J., Alsenz, H., Bornemann, A., Bottini, C., Brassell, S. C., Farnsworth, A., Forster, A., Huber, B. T., Inglis, G. N., Jenkyns, H. C., Linnert, C., Littler, K., Markwick, P., McAnena, A., Mutterlose, J., Naafs, B. D. A., Püttmann, W., Sluijs, A., van Helmond, N. A. G. M., Vellekoop, J., Wagner, T., and Wrobel, N. E.: Cretaceous sea-surface temperature evolution: Constraints from TEX 86 and planktonic foraminiferal oxygen isotopes, Earth-Science Reviews, 172, 224–247, https://doi.org/10.1016/j.earscirev.2017.07.012, 2017.de Winter, N. J., Müller, I. A., Kocken, I. J., Thibault, N., Ullmann, C. V., Farnsworth, A., Lunt, D. J., Claeys, P., and Ziegler, M.: Absolute seasonal temperature estimates from clumped isotopes in bivalve shells suggest warm and variable greenhouse climate, Commun Earth Environ, 2, 1–8, https://doi.org/10.1038/s43247-021-00193-9, 2021.

In addition to the type species, Binkhorstia ubaghsii, which is fairly common in the upper part of the Nekum Member (Maastricht Formation) in the wider vicinity of Maastricht (the Netherlands) and Binkhorstia euglypha, which appears to be restricted to the overlying Meerssen Member of the same formation (uppermost Maastrichtian), a third member, B. desaegheri nov. sp., is recorded from the upper middle Santonian of the Campine area in north-east Belgium. The history of Binkhorstia is convoluted, serving as a prime example of how attempts to unravel the higher-level taxonomic position of late Mesozoic crabs may prove difficult. Over time, the genus has been referred to various families or subfamilies, either podotreme or putative eubrachyuran; here the new family Binkhorstiidae is placed in the superfamily Retroplumoidea. Binkhorstiids appear to have been a relatively short-lived endemic group that fell victim to Cretaceous‒Paleogene (K/Pg) boundary perturbations.