Image: The compound eyes of a living insect — a predatory robber fly — showing the individual lenses. Peter Hudson (South Australian Museum)

When paleontologists uncovered 515-million-year-old fossils on Kangaroo Island, South Australia, they saw something that resembled the eyes of a recently swatted fly. But what they were actually looking at were fossil compound eyes that may have belonged to a large shrimp-like creature that existed prior to the ‘Cambrian Explosion’ of life that began around 540 million years ago.

That finding, according to an international team led by scientists from the South Australian Museum and the University of Adelaide, demonstrates that primitive animals must have had excellent vision.

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A half-billion-year-old fossil compound eye, showing exquisite detail of the visual surface (the individual lenses can be seen as darker spots). John Paterson (University of New England)

Modern insects and crustaceans have compound eyes that consist of hundreds or even thousands of separate lenses, through which they see the world as pixels. Each lens produces a pixel of vision, so more lenses produce more pixels and better visual resolution. However, contrary to what Hollywood would have you believe, each lens does not produce its own image.

The fossil compound eyes found on Kangaroo Island have over 3,000 lenses, making them more powerful than anything from that era, and probably belonged to an active predator that was capable of seeing in dim light. Their discovery suggests that some of the earliest animals possessed very powerful vision, similar to eyes found in many modern insects like robber flies. Sharp vision must therefore have evolved very rapidly, soon after the first predators appeared during the Cambrian Explosion.

Given the tremendous adaptive advantage conferred by sharp vision for avoiding predators and locating food and shelter, there must have been tremendous evolutionary pressure to elaborate and refine visual organs.

While no one really knows who owned this particular pair of eyes, other fossils found in the same rock were from a dazzling array of ancient marine creatures, many new to science. They included primitive trilobite-like creatures, armored worms, and large swimming predators with jointed feeding appendages.

Having eyes that could see 3,000 pixels must have given the creature a huge visual advantage over its contemporaries, which would have seen a very blurry world with about 100 pixels. For comparison, the horseshoe crab sees the world in 1,000 pixels. However, dragonflies, which have the best compound eyes, are able to see the world as ~28 000 pixels.

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