This strange-looking creature is a trilobite, an extinct sea animal very distantly related to modern crustaceans such as woodlice and lobsters. It is about 360 million years old.
It has very large eyes with multiple lenses, characteristic of this and related species of trilobite. They are similar to the compound eyes of modern insects, but much more sophisticated and unlike any other eye in the animal kingdom because they are made of a mineral called calcite.
Calcite is not the best substance for eye lenses as it splits lights into two separate paths. It was used because calcite was the only bio-mineral that trilobites could produce: evolution made the best of a bad job, and spectacularly so. The arrangement of the lenses here improves focus, removes astigmatism and distortion, and cancels out the problem of the split light paths. This optical solution wasn’t re-invented by humans until work on telescopes in the 17th century.
In 2013, while the Oxford University Museum of Natural History is closed to have the roof fixed, some of the exhibits have sneaked away to the town centre!
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