The rise and fall of the Eocene fly genus Kelneria (Diptera, Keroplatidae)

The extinct Eocene fly genus Kelneria Matile, 1979 is characterized by extreme modification of male genitalia within the family Keroplatidae. However, their morphology has remained poorly understood, as fossil material cannot be examined using traditional entomological techniques. To overcome this limitation, we applied micro-computed tomography (µCT) and synchrotron radiation micro-computed tomography (SRµCT) to reconstruct the genitalia through segmentation of scan data, enabling reassessment of the spatial organization and homology of their structures. Our analyses indicate that Kelneria was both morphologically distinctive and well represented in Eocene amber assemblages. They also support the synonymization of the Oise amber genus Eokelneria Hebert, Ngô-Muller & Nel, 2025 with Kelneria Matile, 1979, demonstrating that the characters used to establish Eokelneria fall within the range of variation observed in Kelneria . We further demonstrate that the species-level diversity of Kelneria has been underestimated and describe three new species: Kelneria rovnensis Pełczyńska & Perkovsky sp. nov ., K. erroris Pełczyńska, Krzemiński & Soszyńska sp. nov . and K. szymoni Pełczyńska, Krzemiński & Soszyńska sp. nov . Additionally, identification of representatives in Rovno and Oise ambers extends the geographic and temporal range of the genus to the early Eocene (c. 53 Ma). Taken together, these findings show that Kelneria was an abundant, diverse, and widespread genus in the Eocene but has no modern representatives. The reasons for this extinction remain unknown; however, contrasting distribution of Eocene and extant representatives of the tribe Robsonomyiini suggests that this disappearance may reflect a broader faunal turnover in Europe after the Eocene.