The first fossil Hybocephalini (Coleoptera: Staphylinidae: Pselaphinae) from the middle Eocene of Europe and its evolutionary and biogeographic implications

The extant tropical tribe Hybocephalini is a morphologically highly derived group of the subfamily Pselaphinae (Coleoptera: Staphylinidae), which is characterized most notably by the modified squamous setae that cover various parts of the body. Ten genera and 69 extant species have been found in the Afrotropical and Oriental regions, with one species found in northern Australia. Prior to this study the evolutionary history of the tribe has been remained elusive due to the dearth of known fossils. Here, we describe the first fossil representative of Hybocephalini, Europharinodes schaufussi Yin & Cai gen. et sp. nov. , based on an adult male preserved in Baltic amber ( ca 45.0–38.0 Ma). Using X-ray microtomography, the anatomy including the endoskeletal structures of the head, the full pattern of foveation, and the aedeagus of the beetle were reconstructed. Europharinodes shares most derived traits that are congruent with extant members of Hybocephalini, but it also possesses plesiomorphic and autapomorphic characters unknown in living relatives. In order to constrain the phylogenetic placement of Europharinodes , we created an updated morphological character matrix to explore relationships among this genus and related groups. A monophyletic Hybocephalini was recovered by maximum likelihood and parsimony analyses, with Europharinodes being well-resolved as sister to all modern relatives in the likelihood tree. The fossil thus sheds new light on the morphological evolution of Hybocephalini and suggests a broader palaeodistribution of the tribe during the middle Eocene. The disjunct distribution of an Eocene Baltic amber species and an extant Afrotropical-Oriental distribution of the tribe is probably relictual, and was shaped by global cooling during the Eocene–Oligocene transition.