The Paleocene-Eocene boundary (55.8 Ma) is associated with the Paleocene-Eocene Thermal Maximum (PETM), which is characterized by a negative Carbon Isotope Excursion (CIE), reflecting a major perturbation of the carbon cycle, and by an extreme and rapid global warming. The Cap d'Ailly area (Upper Normandy, France), in which previous studies have revealed the Paleocene-Eocene transition, is a reference locality for organic-rich terrestrial and lagoonal deposits of the-Sparnacian‖ stage, widespread in Northwestern Europe. In this study, we focus on the organic matter content of the Vasterival section. Organic data (Rock-Eval, palynofacies, biomarker analyses and compound specific isotope analyses) were acquired in order to constrain the paleoenvironmental and paleohydrological changes that occurred at the Paleocene-Eocene boundary. Stable carbon isotope compositions of higher plant leaf wax n-alkanes reveal a CIE of-4.5 ‰, extending throughout the second half of the studied section. Palynofacies observations reveal: (i) an abrupt shift from a closed, quiescent marsh pond to an open eutrophic swamp subjected to algal blooms, concomitant with the onset of the CIE; and (ii) the evolution from a swamp to a tidal flat due to the marine transgression that occurred during the PETM. Higher plant biomarkers and their hydrogen isotopic composition compared to nitrogen analyses suggest: (i) dry episodes just before the PETM that may help to understand the triggering of this hyperthermal event; (ii) a moister climate associated with a stronger seasonality during the early PETM.

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Feathers are amongst the most complex epidermal structures known, and they have a well-documented evolutionary trajectory across non-avian dinosaurs and basal birds. Moreover, melanosome-like microbodies preserved in association with fossil plumage have been used to reconstruct original colour, behaviour and physiology. However, these putative ancient melanosomes might alternatively represent microorganismal residues, a conflicting interpretation compounded by a lack of unambiguous chemical data. We therefore used sensitive molecular imaging, supported by multiple independent analytical tests, to demonstrate that the filamentous epidermal appendages in a new specimen of the Jurassic paravian Anchiornis comprise remnant eumelanosomes and fibril-like microstructures, preserved as endogenous eumelanin and authigenic calcium phosphate. These results provide novel insights into the early evolution of feathers at the sub-cellular level, and unequivocally determine that melanosomes can be preserved in fossil feathers.

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