54 million year-old fossil flies yield new insight into the evolution of sight

phys.org | 8/7/2019 | Staff
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Fossilised flies that lived 54 million years ago have revealed a surprising twist to the tale of how insects' eyes evolved. These craneflies, unveiled in Nature today, show that insect eyes trap light the same way as human eyes, using the pigment melanin—yet another example of evolution finding similar solutions to similar problems.

Evolutionary biologists have always been fascinated by eyes. Charles Darwin, anticipating the sceptics, devoted a long explanation of how random mutation followed by natural selection could readily fashion such "organs of extreme perfection." It is not surprising that these useful adaptations have evolved repeatedly across the animal kingdom—octopuses and squids, for instance, have independently acquired eyes uncannily similar to ours.

Vision - Animals - Today - Photoreceptors - Kind

Vision is so vital that most animals today have photoreceptors of some kind. Notable exceptions include creatures that live in total darkness, such as in caves or the deep ocean.

Yet the fossil record of eyes is very poor. The rock record generally preserves hard parts such as bones and shells. Eyes and other soft tissues, such as nerves, veins and intestines, are preserved only under exceptional circumstances.

Eyes - Icons - Evolution - Discovery - Eyes

Because eyes are icons of evolution yet rarely fossilized, the discovery of perfectly preserved eyes from 54 million-year-old insects is noteworthy. In their new study, researchers led by Johan Lindgren of Lund University in Sweden collected and analyzed eyes from 23 craneflies – long-legged relatives of pesky houseflies.

The fossils were exquisitely preserved in sediments containing high levels of fine-grained volcanic ash. They were unearthed in what is now chilly Denmark, but back then was a tropical paradise with abundant insect life.

Eyes - Eyes - Way - Back - Eyeball

The fossilized eyes were surprisingly similar to our own eyes in one important way. The back of our eyeball, called the choroid, is dark and opaque; this protects against ultraviolet radiation and also stops stray light bouncing around and interfering with vision. In...
(Excerpt) Read more at: phys.org
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