The earliest crown therevid lineage: bridging the gap of early evolution of stiletto flies

Therevidae is a diverse family of lower Brachycera, yet its early evolutionary history remains poorly understood due to the absence of available Mesozoic fossils. Here, we describe † Paleothereva longicoxa gen. et sp. nov. from mid-Cretaceous Kachin amber, representing the oldest member of known derived therevids. Phylogenetic analysis and morphological comparisons integrating both extant and fossil species, consistently place this fossil within Taenogera genus-group of Agapophytinae.

This finding indicates that Agapophytinae had already diverged by the mid-Cretaceous, suggesting an earlier origin of Therevidae than previously inferred from molecular data. The occurrence of Paleothereva on the Gondwanan-derived West Burma Block further supports the hypothesis that the ancestors of Agapophytinae — or possibly the broader Agapophytinae + Therevinae clade — originated in Gondwana. Ancestral character state reconstruction of female terminalia within therevid flies reveals that Paleothereva and extant relatives likely shared similar oviposition behaviors associating with sandy-soil environments, which may have driven the corresponding specialization and diversification of acanthophorite spines in female.

These new findings provide rare, direct evidence illuminating the early evolution of derived therevid lineages.