Five hundred million years ago, the oceans teemed with trillions of trilobites—creatures that were distant cousins of horseshoe crabs. All trilobites had a wide range of vision, thanks to compound eyes—single eyes composed of tens to thousands of tiny independent units, each with their own cornea, lens and light-sensitive cells. But one group, Dalmanitina socialis, was exceptionally farsighted. Their bifocal eyes, each mounted on stalks and composed of two lenses that bent light at different angles, enabled these sea creatures to simultaneously view prey floating nearby as well as distant enemies approaching from more than a kilometer away.