Fossils revealed new information about feeding strategies of mayfly nymphs 250 millions yeas ag
Mayflies constitute a very ancient group of insects; fossils of their relatives can be hundreds of millions years old. Scientists from Biology Centre and Natural History Museum in Stuttgart studied unique fossils of mayfly nymphs from the Triassic (early Mesozoic).
Vogesonympha ludovici, photo of the fossil specimen (Milan Pallmann)
We found evidence that nymphs of some species lived in flowing water and acquired food by filtering particles transported by the current.
They possessed a special equipment for such a behavior, consisting of dense rows of long setae on forelegs, well-distinguishable on the studied fossils.
One row of these setae was directed upward and the other downward, together forming a sieve, exposed to the current and collecting food particles. The nymph dwelled on the river bottom with its forelegs spread apart and waiting for the current to bring enough food (consisting of small particles of organic matter).
Similar feeding strategy can be found in many species of aquatic insects today. There are even living mayfly nymphs exhibiting strikingly similar arrangement of a filtering apparatus to what we found in the Mesozoic fossils. However, those lineages are not closely related and such apparatus certainly evolved several times independently.
It has been unknown that this feeding strategy already existed almost 250 millions years ago. Our findings thus represent the earliest evidence for filter-feeding within aquatic insects.
Vogesonympha ludovici, reconstruction of nymph with well-apparent filtering apparatus (drawing by Petr Veselý)
Sroka P., Staniczek A.H. (2022) Evolution of filter-feeding in aquatic insects dates back to the Middle Triassic: new evidence from stem-group mayflies (Insecta, Ephemerida) from Grès à Voltzia, Vosges, France. Papers in Palaeontology, e1456.