Fossil bioinclusions in amber are invaluable source of information on the past evolution and diversity of various organisms, as well as on the paleoecosystems in general. The click-beetles, Elateridae, which originated and greatly diversified during the Mesozoic, are mostly known from the adpression-like fossils, and their diversity in the Cretaceous ambers is only poorly documented. In this study, we describe a new click-beetle based on an incomplete inclusion in ajkaite, an Upper Cretaceous (Santonian) amber from the Ajka Coal Formation from Hungary. We used X-ray micro-computed tomography scanning to reconstruct its morphology because it is deposited in an opaque piece of amber. Our results suggest that the newly described Ajkaelater merkli gen. et sp. nov. belongs to subfamily Elaterinae. It represents the first Mesozoic beetle reported from Hungary, and the first Mesozoic Elateridae formally described from mainland Europe. Our discovery supports an Eurasian distribution and diversification of Elaterinae already in the Cretaceous. The paleoenvironment of the Ajka Coal Formation agrees well with the presumed habitat preference of the new fossil taxon. The discovery of a presumably saproxylic click-beetle shed further light on the yet poorly known paleoecosystem of the Santonian present-day western Hungary.

Department of Applied and Environmental Chemistry Interdisciplinary Centre of Excellence University of Szeged Rerrich Béla tér 1 6720 Szeged Hungary

Department of Entomology Faculty of Biology Moscow State University Leninskie gory 1 12 Moscow Russia 119234

Department of Palaeontology Institute of Geography and Earth Sciences ELTE Eötvös Loránd University Pázmány Péter sétány 1 C Budapest 1117 Hungary

Department of Paleontology and Geology Hungarian Natural History Museum Ludovika tér 2 Budapest 1083 Hungary

Department of Zoology and Ecology Hungarian University of Agriculture and Life Science 1 Páter K str 2100 Gödöllő Hungary

Department of Zoology Faculty of Science Palacky University 17 listopadu 50 771 46 Olomouc Czech Republic

Institute for Geological and Geochemical Research Research Centre for Astronomy and Earth Sciences Eötvös Loránd Research Network 1112 Budaörsi Street 45 Budapest Hungary

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