The genus Macrocera (Diptera: Keroplatidae) is highly diverse, comprising over 200 species distributed worldwide, yet it remains poorly documented in the extensive sciaroid fossil record. This study presents the results of our investigation of Macrocera in Baltic amber, which led to the discovery of five new species (Macrocera barteki Pełczyńska sp. nov., Macrocera hoffeinsorum Pełczyńska, Krzemiński, & Soszyńska sp. nov., Macrocera poseidonis Pełczyńska, Krzemiński, & Soszyńska sp. nov., Macrocera stuckinamberi Pełczyńska, Krzemiński, & Soszyńska sp. nov., and Macrocera tymoni Pełczyńska sp. nov.) and to the re-examination of the only previously described valid species, Macrocera electricornis. A diagnostic key for species identification is provided. Our results indicate that Macrocera had already attained its modern morphological body plan by the Eocene, highlighting Baltic amber as a largely unexplored source of information on the evolutionary history of certain insect groups. We further discuss the delimitation of the genus and emphasise the need for its comprehensive revision.

Key words: Diptera, Keroplatidae, fossil insects, paleodiversity, Baltic amber, Eocene.

Alicja Pełczyńska [alicja.pelczynska@edu.uni.lodz.pl; ORCID: https://orcid.org/0000-0002-7000-3552], University of Lodz, Faculty of Biology and Environmental Protection, Department of Invertebrate Zoology and Hydrobiology, 90-237 Łódź, Poland; University of Copenhagen, Faculty of SCIENCE, Natural History Museum of Denmark, 2100 Copenhagen, Denmark. Wiesław Krzemiński [wieslawk4@gmail.com; ORCID: https://orcid.org/0000-0001-5685-891X], Institute of Systematics and Evolution of Animals, Polish Academy of Sciences, 31-016 Kraków, Poland. Agnieszka Soszyńska [agnieszka.soszynska@biol.uni.lodz.pl; ORCID: https://orcid.org/0000-0002-2661-6685], University of Lodz, Faculty of Biology and Environmental Protection, Department of Invertebrate Zoology and Hydrobiology, 90-237 Łódź, Poland.