The mid-Maastrichtian carbon isotope event (MME), dated at ∼69 Ma, reflects a perturbation of the global carbon cycle that, in part, correlates with the enigmatic global extinction of ‘true’ (i.e., non-tegulated) inoceramid bivalves. The mechanisms of this extinction event are still debated. While both the inoceramid extirpation and MME have been recorded in a variety of deep-sea sites, little is known about their expression in epicontinental chalk seas. In order to study the shallow-marine signature of the MME in this epicontinental shelf sea, we have generated quantitative foraminiferal assemblage data for two quarries (Hallembaye, NE Belgium; ENCI, SE Netherlands) in the Maastrichtian type area, complemented by a species-specific benthic δ13C record. In contrast to deep-sea records, no significant changes in benthic foraminiferal assemblages and benthic foraminiferal accumulation rates are observed across the MME in the type-Maastrichtian area. At the Hallembaye quarry, the otherwise rare endobenthic species Cuneus trigona reaches a transient peak abundance of 33.3% at the onset of the MME, likely caused by a local transient change in organic matter flux to the seafloor. Nevertheless, high and near-constant species evenness shows that neither oxygen nor organic matter flux was limited across the extinction level or during the MME. Benthic foraminiferal data from the uppermost part of the studied section, above the MME, indicate a significant increase in food supply to the seafloor. Decreased amounts of terrigenous elements across this interval document a lesser riverine or aeolian influx, which means that the increased benthic productivity is linked to a different origin. Potentially, the continuous precipitation of chalk under nutrient-poor conditions in the Late Cretaceous chalk sea was enabled by efficient nutrient recycling in the water column. In shallower depositional settings, nutrient recycling took place closer to the seafloor, which allowed more organic matter to reach the bottom. These results provide insights in the importance of nutrient cycling for biological productivity in the NW-European chalk sea.
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Over the last decade, the petrous bone (petrosum) has become the ultimate repository of ancient biomolecules, leading to a plea for a more ethical curation preventing the systematic destruction of this bioarchaeological archive. Here, we propose to explore the biosystematic signal encompassed in the biological form of 152 petrosa from modern populations of wild and domestic sheep landraces/breeds across Western Europe, South-Western Asia and Africa, using high resolution geometric morphometrics (GMM) and the latest development in 3D virtual morphology. We assessed the taxonomic signals among wild and domestic caprine species and sheep landraces. We also explored the effect of sexual dimorphism and ageing at the population scale. Finally, we assessed the influence of climatic factors across the geographic distribution of our dataset using Köppen-Geiger climate categories. We found that the 3D form of petrous bones can accurately separate wild and domestic caprine taxa and that it is not influenced by sexual dimorphism, post-natal ageing or horn bearing. Recent selective breeding has not induced sufficient diversification to allow accurate identification of the different landraces/breeds in sheep; however, both genetic distance and climatic differences across the current distribution in sheep landraces/breeds strongly contribute to petrosum intraspecific variation. Finally, human mediated dispersal of domestic sheep outside their Near Eastern cradle, especially towards Africa, have greatly contributed to the diversification of sheep petrous bone form and shape. We therefore highly recommend systematic 3D surface modelling of archaeological petrosa with preliminary GMM studies to help target and reduce destructive biomolecular studies.
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