Abstract:
Several Paleocene to Oligocene maar lake deposits in Central Europe provide exceptional windows into past ecosystems. Fossilized floral and faunal remains from these sites enable the reconstruction of a paratropical climate in Europe during the Paleocene to Eocene, followed by a transition to cooler conditions in the Oligocene. Direct evidence of flower-insect interactions is rare in the fossil record, and studies on pollination biology in the Paleogene are largely lacking. By extracting in situ and/or adhered pollen grains from fossilized flowers and insects preserved within the same geological formations, it is possible to establish ecological links between these organismal groups. Fossils are examined using epifluorescence stereomicroscopy, and pollen is meticulously extracted using fine needles. The recovered pollen is then analyzed using light microscopy, scanning electron microscopy, and transmission electron microscopy. Due to the conservative and often taxonomically distinctive morphology of pollen, fossilized pollen grains can be used to: (1) assign previously unidentified flowers to extant taxa at the family, genus, or species level, and (2) infer the plant taxa visited by insects prior to their death and fossilization. Using this methodology, several hundred fossils from four Paleocene to Oligocene localities in France and Germany were examined. These include Menat (Late Paleocene, ~58 Ma), Messel (late Early Eocene, ~48 Ma), Eckfeld (Middle Eocene, ~44 Ma), and Enspel (Late Oligocene, ~24 Ma). Among the specimens studied were over 1,700 flowers (638 bearing pollen) and over 1,500 insects (273 with associated pollen). The flowers are attributable to over 50 extant angiosperm families. Among the insect taxa, Coleoptera (beetles) are most abundant, followed by Hymenoptera (bees, wasps), Diptera (flies), and a limited number of Lepidoptera (butterflies, moths). Several cases illustrate well-established flower-insect associations as early as the Paleogene: Parthenocissus (Vitaceae) was detected across all major pollinator groups, particularly among Diptera. Apiformes (Hymenoptera) showed a specific association with the subfamily Tilioideae (Malvaceae). Ludwigia (Onagraceae) was visited by beetles of the families Buprestidae and Scarabaeidae.
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