New fossil wasp species from the earliest Eocene Fur Formation has its closest relatives in late Eocene ambers (Hymenoptera, Ichneumonidae, Pherhombinae)

Noah Meier,Anina Wacker,Seraina Klopfstein

doi:10.18061/bssb.v1i1.8427

Abstract

Darwin wasps (Ichneumonidae) are one of the most species-rich insect families but also one of the most understudied ones, both in terms of their extant and extinct diversity. We here use morphometrics of wing veins and an integrative Bayesian analysis to place a new rock fossil species from the Danish Fur Formation (~54 Ma) in the tree of Darwin wasps. The new species, Pherhombus parvulus n. sp., is placed firmly in Pherhombinae, an extinct subfamily so far only known from Baltic and Rovno-Ukranian ambers, which are estimated to be 34–48 Ma and 34–38 Ma, respectively. Our phylogenetic analysis recovers a subfamily clade within the higher Ophioniformes formed by Pherhombinae, Townesitinae, and Hybrizontinae, in accordance with previous suggestions. Due to the placement of the new species as sister to the remaining members of Pherhombinae, we argue that our finding is not at odds with a much younger, late Eocene age (~34–41 Ma) of Baltic amber and instead demonstrates that Pherhombus existed over a much longer period than previously thought. Our results also exemplify the power of wing vein morphometrics and integrative phylogenetic analyses in resolving the placement even of poorly preserved fossil specimens.

Highlights

IntroductionDarwin wasps (Ichneumonidae) are assumed to have one of the largest gaps between the number of described species and the actual species diversity (Klopfstein et al 2019b)
Insect taxonomy in the past centuries was strongly biased towards large and colourful species and overrepresented Lepidoptera and Coleoptera
In the light of our results, we describe the new fossil species in the genus Pherhombus and discuss the implications of this finding on the potential age of Baltic amber and on the quality of fossil placements based on combined Bayesian analyses

Summary

Introduction

Darwin wasps (Ichneumonidae) are assumed to have one of the largest gaps between the number of described species and the actual species diversity (Klopfstein et al 2019b). The fossil record of ichneumonids goes back to the Lower Cretaceous, about 120-130 Ma, while a recent dating study placed the origin of the family and most of its subfamilies in the Jurassic (about 181 Ma; Spasojevic et al 2021). The fossil record of Darwin wasps is even more under-researched than their extant diversity, which impedes inferences about their past diversity and evolutionary history. We describe an approximately 54 Ma old ichneumonid rock fossil species from the Danish Fur Formation (Rust 1998). Its forewing venation with a large, rhombic areolet is rather rare among members of the family, both extant and extinct, and makes it unique among the known Fur Formation ichneumonids

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Conclusion