A new Cretaceous genus of xyelydid sawfly illuminating nygmata evolution in Hymenoptera
1 College of Life Sciences, Capital Normal University, 105 Xisanhuanbeilu, Haidian District, Beijing 100048, China
2 Palaeontological Institute, Russian Academy of Sciences, 123, Profsoyuznaya ul, Moscow 117997, Russia
3 Department of Palaeontology, Natural History Museum, Cromwell Road, London SW7 5BD, UK
BMC Evolutionary Biology 2014, 14:131 doi:10.1186/1471-2148-14-131Published: 17 June 2014
Nygmata are prominent glandular structures on the wings of insects. They have been documented in some extant insects, including several families of Neuroptera and Mecoptera, the majority of Trichoptera, and a few of the hymenopteran Symphyta. However, because nygmata are rarely preserved in compression fossils, their early development and evolution are still enigmatic. For example, the only documented nygmata in the Hymenoptera are on the forewings of the Triassic xyelids Asioxyela paurura and Madygenius primitives.
This study describes and illustrates a new genus and species from the family Xyelydidae, Rectilyda sticta gen. et sp. nov., from the Early Cretaceous Yixian Formation of Duolun County, Inner Mongolia, China. This genus has 1-RS reclival and linearly aligned with 1-M, which is different from all other genera in the Xyelydidae. In addition, R. sticta gen. et sp. nov. has clearly preserved nygmata: four symmetrical nygmata on each forewing and two on each hind wing.
Previous reports of nygmata on the forewings of Triassic xyelids and extant sawflies, together with this new fossil record of nygmata, provide rare insights into their developmental trends, as well as into the evolution of hymenopterans and insects in general.