A 530 million-year-old fossil contains what could be the oldest eye found on any creature, scientists say.
The remains of an extinct sea creature include an early form of the eye seen in many of today's animals, including crabs, bees and dragonflies.
A fossil of a hard-shelled animal called a trilobite was found in Estonia, which appeared to have a compound eye made up of around 100 separate visual cells.
The team, which includes a researcher from Edinburgh University, say their discovery shows compound eyes have changed little in more than 500 million years.
Professor Euan Clarkson, of the university's School of GeoSciences, said: "This exceptional fossil shows us how early animals saw the world around them hundreds of millions of years ago.
"Remarkably, it also reveals that the structure and function of compound eyes has barely changed in half a billion years."
The species would have had poor vision compared with many animals today but it could still identify predators and obstacles in its path.
The team's study is published in the journal Proceedings of the National Academy of Sciences.
It was carried out in collaboration with Cologne University in Germany and Tallinn University of Technology in Estonia.
Professor Brigitte Schoenemann, of Cologne University, said: "This may be the earliest example of an eye that it is possible to find.
"Older specimens in sediment layers below this fossil contain only traces of the original animals, which were too soft to be fossilised and have disintegrated over time."