Revisions, new taxa, and venation transformations of the sawfly family Blasticotomidae sensu lato (Hymenoptera: Tenthredinoidea) highlight the evolution of the basal Hymenoptera

Abstract Wing venation pattern is particularly important in the taxonomy and classification of insects, especially for fossil material. There are recognized transformation series that apparently often represent a mainstream in the evolutionary trend of the wing venation of Hymenoptera. One notable instance is the gradual reduction of the subcosta veins from multiple branches to their total absence. Herein, we place four new genera and six new species in the family Blasticotomidae (=Xyelotomidae) of Hymenoptera. They are Xyelocerus abruptus sp. nov., Liberitoma tenella gen et sp. nov., Liberitoma compta sp. nov., Liberitoma incompleta sp. nov., Aduantoma insolita gen. et sp. nov., and Apertoma gen. nov. from the Middle Jurassic of China, and Enspeletoma oligocaenica gen. et sp. nov. from the Upper Oligocene of Germany. The newly discovered species of Liberitoma from China possessed a supernumerary hind branch of vein Sc in its forewing, which has apparently never been recorded before in other hymenopterans, and the unique venation pattern of Aduantoma suggests the possibility of two additional steps of vein Sc transformation before its complete loss. Based on the new findings, Blasticotomidae are proposed to be divided into four subfamilies: Blasticotominae Thomson 1871, Dahurotominae subfam. nov., Pseudoxyelocerinae subfam. nov., and Undatominae subfam. nov.