Ichneumonid parasitoid wasps from the Early Eocene Green River Formation: five new species and a revision of the known fauna (Hymenoptera, Ichneumonidae)

Abstract

The parasitoid wasp family Ichneumonidae is one of the most species-rich groups of organisms, but its fossil record remains very poorly studied, which impedes inferences of the origin of its diversity. We here describe two new fossil genera and five new species of Ichneumonidae from the Eocene Green River Formation: Carinibus molestus gen. et sp. nov., Ichninsum appendicrassum gen. et sp. nov., Mesoclistus? yamataroti sp. nov., Scambus? mandibularis sp. nov., and Scambus? parachuti sp. nov. The newly described Mesoclistus? yamataroti represents the first record of the subfamily Acaenitinae from this fossil locality. In addition, we revise the ten previously described fossil ichneumonids from the Green River Formation, following a conservative approach when re-assessing their taxonomic positions: we keep the current placement of six revised fossils, but express the uncertainty in genus-assignment according to open nomenclature rules: Eclytus? lutatus Scudder, Glypta? transversalis Scudder, Pimpla? eocenica Cockerell, Phygadeuon? petrifactellus Cockerell, Plectiscidea? lanhami Cockerell and Rhyssa? juvenis Scudder. We exclude three fossil genera from their current subfamilies and place them within Ichneumonidae incertae subfamiliae: Eopimpla Cockerell, Lithotorus Scudder and Tilgidopsis Cockerell. Furthermore, we move Tryphon amasidis Cockerell and LeVeque to the new genus Trymectus gen. nov. In the light of these revisions, we discuss the importance of careful taxonomic placement of fossils and difficulties in ichneumonid palaeontology caused by host-related homoplasies and a lack of knowledge about the age of the recent subfamilies.