A cretaceous fly trap? remarkable abdominal modification in a fossil wasp

Summary

Phylogenetic position of †Sirenobethylus gen. nov.We describe a new genus †Sirenobethylus, from mid-Cretaceous Kachin amber, based on sixteen specimens. The new genus is readily attributed to the Aculeata by its concealed posterior abdominal segments and ovipositor apparatus [28]. †Sirenobethylus has 9 flagellomeres and forewing with 8 closed cells, which is different from Vespoidea sensu lato [29] and Apoidea (antenna with 10 flagellomeres in female and forewing usually has 10 or 9 closed cells) [30, 31]. Therefore, †Sirenobethylus probably belongs to Chrysidoidea. We retrieve this superfamily as monophyletic (Fig. 4, Additional file 1: Dataset S2) [32], unlike some recent molecular studies [33].All †Sirenobethylus specimens examined are macropterous females; given the unique diagnostic traits in, e.g., wing venation, and the somewhat isolated phylogenetic position of the new taxon (Fig. 4), it is not possible to associate these females with any males known from Kachin amber. They have the forewing venation similar to †Chrysopsenellidae, including a long pterostigma, a closed subdiscal cell, and vein 2 m-cu absent (Fig. 1A and D). Therefore, the new genus is much more similar to †Chrysopsenellidae than extant groups. However, †Sirenobethylus has comparatively complete hind wing venation, including two closed cells also exhibited by †Plumalexiidae and Plumariidae, but different from other groups of Chrysidoidea [34]. All these features suggest that †Sirenobethylus could be a stem group of Chrysidoidea, which is consistent with our phylogenetic analyses (Fig. 4, Additional file 3: Table S2). Furthermore, †Sirenobethylus has a unique combination of diagnostic characters within Chrysidoidea. For these reasons, we place †Sirenobethylus charybdis gen. & sp. n. in its own family, the †Sirenobethylidae.Possibly function of the abdominal apparatusThe abdominal apparatus of †Sirenobethylus, including the sixth sternum and the seventh tergum and sternum, form three superimpos...