New Fossil Xyelidae (Hymenoptera: Symphyta) from the Mesozoic of Northeastern China

Simple Summary One new genus and two new species, described from new fossil specimens of northeastern China, enhance our knowledge of the Xyelidae in the mid-Mesozoic. A key to the genera of Angaridyelini and a table of known fossil species of Macroxyelinae are provided. After investigating various angles between Rs+M and 1-Rs for known fossil species of Macroxyelinae, we report that the angle and the length of 1-Rs are correlated. In addition, we believe that the tribe Ceroxyelini may have only one genus of Ceroxyela, and suggest that Isoxyela and Sinoxyela should be transferred to Gigantoxyelini. One new genus and species, Leptoxyela eximia gen. et sp. nov., and one new species, Scleroxyela cephalota sp. nov., are described and illustrated based on two well-preserved compression fossils from the Lower Cretaceous Yixian Formation and the Middle Jurassic Jiulongshan Formation of China, respectively. Leptoxyela eximia gen. et sp. nov. is placed in the tribe Angaridyelini, 1966 and Scleroxyela cephalota sp. nov. in the tribe Xyeleciini Benson, 1945; while both tribes are in the subfamily Macroxyelinae Ashmead, 1898 of Xyelidae. A key to the genera of Angaridyelini is provided. In addition, we investigated various angles between Rs+M and 1-Rs for known fossil species of Macroxyelinae, and we found the angle and the length of 1-Rs are correlated; however, we could not see any correlation between the angles and the fossil ages even within a tribe. Furthermore, based on Sc-2 connected to R before Rs, the angle between Rs+M and 1-Rs, and the length of the first flagellomere, we believe that the tribe Ceroxyelini may have only one genus of Ceroxyela, and suggest that Isoxyela and Sinoxyela should be transferred to Gigantoxyelini.