Mayflies first emerged before the dinosaurs.
The most primitive flying insects alive today, mayflies share many features with their ancient relatives. Due to their short lives and frail nature, most fossils of their ancestors preserve the nymphs. But there are a few fossils of adults in rock or amber; the oldest, dating back 312 million years, was found in sedimentary rocks in Massachusetts, US. Remarkably, this extremely rare fossil is the imprint left by an adult mayfly, rather than the fossilised remains of the creature itself. Presumably it touched down in mud before flying offff.