The first fossil record of the cuckoo wasp genus Primeuchroeus in Eocene Baltic amber, with revision of two fossil Chrysididae (Hymenoptera: Chrysidoidea)

Abstract

Chrysididae fossils are rare and understudied compared to their extant diversity, with an overwhelming proportion of genera found in Cenozoic fossiliferous deposits currently thought to be extinct. Here, we document the oldest known representative of the extant genus Primeuchroeus Linsenmaier, 1968 based on a specimen from Priabonian (upper Eocene) Baltic amber, and described as Primeuchroeus groehni sp. nov. This finding is the oldest Chrysididae fossil indisputably attributed to an extant genus and refutes the hypothesis that modern genera are not older than Neogene in age, as hitherto believed. Additionally, we propose the reallocation of a recently described fossil genus and fossil species. The genus Sphaerocleptes Cockx et al. (2016), described in the subfamily Cleptinae from Cenomanian French amber, is transferred to Chrysidinae, tribe Elampini; this is the first temporal occurrence for the tribe, previously not known earlier than the upper Eocene. The fossil species Hedychridium rosai Brazidec and Perrichot, 2023 is transferred from the subfamily Chrysidinae to Amiseginae and we propose the new combination Atoposega rosai (Brazidec and Perrichot, 2023) comb. nov. These findings provide deep insights into the evolution of Chrysididae: within the Chrysidinae subfamily, established by the mid-Cretaceous, some of the modern generic lineages had already diverged by the upper Eocene, and the Miocene Chrysididae fauna was likely similar to the extant fauna, pending further discoveries. Based on our observations, the fossil record of Chrysididae shows more similarities to that of other diverse hymenopteran families than was previously thought.