Fossil record of the mayfly family Ephemerellidae (Insecta: Ephemeroptera), with description of new species and first report of Ephemerellinae from Baltic amber

The fossil record of the mayfly family Ephemerellidae is reviewed. Of previously described fossil Ephemerellidae, all records but one are doubtful or erroneous. We reinvestigate the holotype of Ephemerella viscata Demoulin, 1968 from Eocene Baltic amber and confirm its previous placement within the subfamily Timpanoginae Allen, 1984, based on the presence of vestigial gill sockets on abdominal segments IV–VII only. It is transferred to the genus Eurylophella Tiensuu, 1935 [Eurylophella viscata (Demoulin, 1968) comb. nov.] based on proportions of the forelegs, elongated abdominal segment IX, and the shape of the subimaginal penis. Additionally, we describe two new specimens from Eocene Baltic amber: Ephemerella trigonoptera sp. nov. represents the first fossil record of subfamily Ephemerellinae. It can be separated from other representatives of Ephemerella Walsh, 1862 sensu lato by the shape of the hind wings, which are remarkably narrowed towards the apex, with a costal projection located rather proximally. The second new specimen, a male subimago, cannot be differentiated from other Ephemerellinae due to its poor preservation. The discovery of Ephemerella trigonoptera sp. nov., together with the taxonomic reassessment of Eurylophella viscata comb. nov., provide the first reliable evidence that both subfamilies of Ephemerellidae, Ephemerellinae and Timpanoginae, date back at least to the Palaeogene. The biogeographical and palaecological implications of these findings are discussed.

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