Back to the Eocene: Ichneumonid wasp palaeo-taxonomy
Ichneumonid wasps from the early Eocene are posing a general question: how confident are we in the taxonomic placement of fossil taxa?
Ichneumonid parasitoid wasps make one of the largest groups of organisms today, with more than 24,000 species described and at least 60,000 estimated. These wasps show a remarkable diversity in morphology, behavior and host choice, as well as parasitoid life style. Nevertheless, the fossil record of the family has been poorly studied and hundreds of fossils await description in palaeontological collections around the world.
At the Natural History Museum in Bern, two young scientists, Tamara Spasojevic and Seraina Klopfstein, are investigating fossil ichneumonids. Their revision of ten already described species from the Green River Formation, USA (~50 Ma) reveals many doubtful placements of fossils, most of which are due to a lack of interpretable characters. Therefore, they recognised the need for expressing uncertainty in the fossil nomenclature and applied this when describing five new ichneumonids from this locality.
In contrast, five remarkably preserved ichneumonids from Messel Pit, Germany (~47 Ma) shed new light on the evolutionary history of the group. They discovered the oldest unambiguous representatives of the extant ichneumonid subfamilies Pimplinae, Rhyssinae and Labeninae, presenting firm evidence for the age of these subfamilies.
Further work involves integrative phylogenetic analysis which includes morphological data from both recent and fossil taxa together with molecular dataset (total evidence dating analysis), as a next step towards the understanding of the evolutionary history of ichneumonids.