Abstract: Menispermaceae are an angiosperm family of mostly climbing plants distributed throughout tropical regions. The fruits in this family have a strong sclerified endocarp and can be used for reliable species-level identifications, even in a fossilized form. New Paleocene-age menispermaceous endocarps have recently been discovered in South America and Asia, while in Europe, they are mostly found in the Eocene. This paper focuses on the study of fossil endocarps belonging to Menispermaceae, found in the Petit-Pâtis locality, which is one of the few Paleocene localities in Europe. The locality is dated to the late Paleocene (57–56 Ma) and the fossils represent flora and fauna in the Paris Basin before the onset of the Paleocene–Eocene Thermal Maximum. Lignitized fossils were photographed and their morphology was analyzed using computed tomography, scanning electron microscope, and geometric morphometric analysis. The analysis of 36 fossils belonging to Menispermaceae revealed that three genera (Stephania, Palaeosinomenium, Tinospora) were present in the late Paleocene of Paris Basin. Differences in internal morphology and a more inflated endocarp base led to a description of a new fossil species—Palaeosinomenium oisensis sp. nov. The occurrence of these genera in the Paleocene of France is consistent with the suggestion that megathermal flora was present in the Paris Basin before the Paleocene–Eocene Thermal Maximum. These three genera are currently the oldest occurrences in Europe, highlighting the connection between paleofloras of the Americas, Europe, and Asia in the Paleocene.

Key words: biogeography, Menispermaceae, paleobotany, Paleocene, taxonomy