How old are the earliest recognizable mayfly fossils?

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A mayfly (Ephemera vulgata) with delicate, veined wings and long tail filaments clings to a green blade of grass against a blurred green background. — mayfly An adult mayfly (*Ephemera vulgata*) in Europe.

The earliest recognizable mayfly fossils date back to the Pennsylvanian Subperiod, which occurred approximately 323.2 million to 298.9 million years ago. These ancient insects appear to have been abundant during the subsequent Permian Period.1