Phylogeny of Mastigitae sheds light on a hundred‐million‐year‐long morphological stasis of the extant genus Clidicus Laporte (Coleoptera: Staphylinidae: Scydmaeninae)

Mastigitae comprise 15 genera, of which seven are extinct, and species of two extant genera are also documented as fossils. The rich fossil record makes Mastigitae exceptional among Staphylinidae. Based on results of phylogenetic analyses comprising 33 extant species, 10 dated fossils and ~300 adult morphological characters, including structures visualized by synchrotron microtomography in mid-Cretaceous and Eocene specimens, we attempt to resolve the phylogeny of Mastigitae. The monophyly of Mastigitae and relationships of Leptomastacini + all remaining Mastigitae, Mastigini + †Baltostigini and Leptochromini + Clidicini are well-supported, but the tribal placement of †Palaeoleptochromus is inconclusive. Mesozoic fossils are unambiguously placed in the extant genus Clidicus, and an Eocene (Priabonian) fossil Clidicus europaeus sp. nov. is described. The evolution of this genus is one of the best morphologically documented examples of a long stasis among beetles. The results demonstrate a continuous existence of Clidicus in Eurasia dated from ~99 Ma, through ~36 Ma to the present time. We hypothesize that ecomorphological sets of structures of Clidicus, including the mouthparts, had reached a functional optimum at least ~100 Ma and then have been preserved in an unchanged form, likely by stabilizing selection in mesic habitats with an abundance of food sources.