Rogue sawflies: rare late Eocene amber fossils provide new calibration points for dating the evolution of Tenthredinoidea (Insecta: Hymenoptera)

True sawflies (Tenthredinoidea) have a substantial fossil record but are rarely encountered in Eocene ambers. Here we describe three new taxa in this superfamily from late Eocene ambers. †<i>Rovnotaxonus aristovi</i> gen. et sp. nov. is the first true sawfly reported from Rovno amber. Based primarily on characters in the fore wing venation, we assign the new taxon to Tenthredinidae: Allantinae: Allantini. We also describe two new species of Diprionidae from Baltic amber: †<i>Eodiprion pectinatus</i> sp. nov. from a female specimen and †<i>Monodiprion gladius</i> gen. et sp. nov. from a male previously reported as †<i>Eodiprion</i> sp. by Schedl (2008); we redescribe †<i>Eodiprion</i> Schedl, 2007 and provide emended diagnoses of the genus and of †<i>Eodiprion groehni</i> Schedl, 2007. We integrate all these fossils as well as †<i>Sambia</i> Vilhelmsen and Engel, 2012 (Tenthredinidae: Tenthredininae) previously described from Baltic amber in a combined data set assembled from previously published morphological and molecular data sets. We analyse the combined data set in a Bayesian framework and implement RoguePlots to evaluate the positions of the fossils. The diprionid fossils are unequivocally placed inside Diprionidae, in a polytomy with extant members of Diprioninae; the Monocteninae, the other subfamily currently recognized in the family, is not retrieved as monophyletic. †<i>Rovnotaxonus</i> is placed inside Allantinae and shares some characters with <i>Taxonus</i>. †<i>Sambia</i> is placed near the base of Tenthredininae. The evaluation of the phylogenetic position of the fossils treated here will make them available for future dating analyses of Tenthredinoidea, helping to further elucidate the evolutionary history of this significant lineage of herbivorous insects. Possible reasons for the comparatively low abundance of true sawflies in late Eocene ambers are discussed. http://zoobank.org/urn:lsid:zoobank.org:pub:81FC994C-B64B-41CB-A4B0-C31EA8CAE310