Last major gap in scydmaenine evolution filled (Coleoptera: Staphylinidae)

The tribe Scydmaenini represents one of the most successful modern groups of the ant-like stone beetles (Scydmaeninae), displaying a high degree of species diversity (>750 species) and morphological disparity. Surprisingly, direct fossil evidence crucial for elucidating the origin and early evolution of Scydmaenini is lacking. This gap of knowledge is of particular interest as the Cretaceous origin of other major scydmaenine lineages, e.g., Mastigini, Eutheiini, Cephenniini, and Glandulariini, were recently documented. Here, we report a new genus and species, Kuafu borealis gen. et sp. nov., from Cretaceous Burmese amber, pushing back the oldest definitive record of stem-group Scydmaenini to approximately 99 Ma. An affinity of the new taxon with recent Scydmaenini is strongly supported by the beetle's short, dome-like terminal (fourth) maxillary palpomeres, as well as an exposed metanepimera which are typical character states of the tribe. However, Kuafu possesses a plesiomorphic un-notched anterior margin of the scape, a character state unknown among living Scydmaenini, and suggesting a basal position of the fossil taxon. Our find provides firm evidence that stem-group Scydmaenini, like other major scydmaenine lineages, originated no later than the mid-Cretaceous, removing the possibility that Scydmaenini may had a young, Quaternary origin.