Echoes from the Cretaceous: new fossils shed light on the evolution of host detection and concealed ovipositor apparatus in the parasitoid wasp superfamily Orussoidea (Hymenoptera)

†Kryptovelona carstengroehni gen. et sp. nov. and †Orussus juttagroehnae sp. nov. are the first female members of the parasitoid wasp family Orussidae recorded from Baltic amber. We describe them, including relevant parts of the internal anatomy examined with synchrotron scanning. The fossils display a number of modifications in the antennae and foreleg correlated with the specialized host-detection mechanism, and in the ovipositor apparatus, as well as in the thorax and abdomen for accommodating the internalized ovipositor. The presence of these and other features places them as crown-group members of the Orussidae, as demonstrated by Bayesian phylogenetic analyses. The recently described stem-group orussoid fossils from Burmese amber, the probable female †Cretorussus vilhelmseni, and probable male †Burmorussus mirabilis (both placed in Burmorussidae), were also included in the dataset. By comparing the new Baltic amber taxa with †Cretorussus, it is possible to trace the progressive refinement of the echolocation mechanism through reductions in the number of antennomeres and foreleg tarsomeres. Unfortunately, †Cretorussus does not have the posterior part of the abdomen with the ovipositor preserved. Nevertheless, it is possible to infer that the putative echolocation mechanism for host detection evolved at least 100 Mya, whereas the concealed ovipositor apparatus has not been documented in fossils older than approx. 35 Mya.