Eye composition of fossil flies surprises researchers

A group of researchers has discovered eumelanin, a natural pigment that is also found in human eyes, in the fossilized eyes of crane flies (Tipulidae) dating back 54 million years ago. It was a surprise for the researchers themselves as it was believed that in arthropods there were no melanin pigments in the visual system.

To underline the surprise of the discovery is Johan Lindgren, lead author of the study and professor in the Department of Geology of the University of Lund: “We were surprised by what we discovered because we weren’t looking for it or we didn’t expect it.” After making the discovery in the fossils, the researchers then examined the eyes of today’s crane flies and found that substance also in these species.

Then comparing the fossilized eyes with the eyes of today’s species, the researchers found that the fossilized eyes were characterized by the presence of calcified homatatid lenses. According to Lindgren, it was this mineral that replaced the original chitinous material in the fossil.

And this has led the researchers themselves to reconsider a widespread hypothesis concerning the evolution of visual systems in animals. Previous research had, in fact, suggested that trilobites, a group of extinct sea arthropods, possessed mineralized lenses during their lifetime.

As Lindgren explains, “the general opinion was that the trilobites had lenses made from single crystals of calcium carbonate. However, they were probably much more similar to modern arthropods because their eyes were mainly biological.”