A transitional fossil sheds light on the early evolution of the Staphylinine group of rove beetles (Coleoptera: Staphylinidae)

摘要

Rove beetles of the Staphylinine group of subfamilies represent the most species-rich clade of Staphylinidae, which in turn is the most speciose beetle family. While several relationships within the Staphylinine group are well supported by morphological and molecular data alike, the basal relationships within the clade remain unresolved. In particular, understanding the largest radiation on the beetle tree of life is complicated by the absence of early-diverging transitional fossils. Here we describe a new genus and species of the Staphylinine group of subfamilies from the Lower Cretaceous Yixian Formation in eastern China (c. 125 Ma). Paroxyporus fossilis Cai gen. et sp. nov. shares a number of characters with the monogeneric subfamily Oxyporinae, namely its prognathous head with prominent apically curved mandibles, contiguous procoxae, moderately separated mesocoxae and abdominal intersegmental membranes with a 'brick-wall' pattern. It, however, shares oval procoxae and 'U'-shaped abdominal impressions with the monogeneric subfamily Megalopsidiinae. A parsimony analysis of 211 morphological characters recovered Paroxyporus gen. nov. as sister to the whole Staphylinine group except Oxyporinae, linking Oxyporinae and other clades of the Staphylinine group, and it seems to be a stem member of the Staphylinine group. As such, Paroxyporus gen. nov. may represent an early-diverging isolated lineage within the Staphylinine group, a lineage that has been recognized on the basis of morphological data but challenged by some recent molecular studies, or alternatively a stem member of the Staphylinine group. Together with described fossil members of the subfamily Oxyporinae, Paederine and Staphylinine from the Yixian Formation, Paroxyporus fossilis gen. et sp. nov. is one of the earliest representatives of the Staphylinine group in the fossil record, providing an important calibration point for understanding the timing of the early diversification of rove beetles in the Mesozoic.