Abstract
The fossil record of chalcid wasps is sparse, which may be explained by rare fossilization of these minute wasps, but also by the extreme difficulty of both finding the fossils and assigning them to a valid taxonomic level. Here, we provide a comprehensive review of the fossils and subfossils of chalcid wasps based on a newly compiled dataset from the literature and unpublished data. We discuss the validity and taxonomic placement of each fossil. We also provide an overview of the environment where fossils occurred through a compilation of past environments and local habitat conditions. Finally, we attempt to synthesize what paleontology currently tells us about the appearance and evolution of the major lineages of chalcid wasps in past ecosystems. The fossil record is represented by 211 species (including 15 unavailable names, and 12 still undescribed, but much more certainly remains to be described). The oldest chalcid fossil taxon is †Cretaxenomerus jankotejai (Protoitidae) and all other species from Lebanese amber but the diversity of the superfamily is not captured until first in Oise amber and then in Baltic amber, with 35 families then present. Many of the initially described species were incorrectly assigned to extant genera and often misclassified at the family level. Most chalcid fossils are described from amber, which often allows for extremely detailed morphological examination. Our results suggest that wasps of Mesozoic age globally are smaller than those trapped in deposits of Cenozoic age, which corroborates phylogenomic hypotheses suggesting that the first lineages of chalcidoids were minute in size and only during the Cenozoic was a larger size evolved.