Dr Brigitte Schoenemann (University of Cologne) and her colleagues Helje Pärnaste (Tallinn, Estonia), and Euan Clarkson (Edinburgh, Scotland) have succeeded in unraveling the structure and functioning of the oldest known compound eye. The researchers used an exceptionally well-preserved fossil trilobite (Schmidtiellus reetae), which is over half a billion years old, showing the cellular structure of a compound eye. It not only shows how this eye was constructed, but also its functioning, its performance, and how it differs from contemporary compound eyes. The results show that modern compound eyes work in ways strikingly similar to those of half a billion years ago. They are very conservative in their structure – and quite successfully so. “The principle of the modern compound eye most likely goes back to before the times of our first fossil records. Half a billion years ago, it was in the early stage of its development, and with our work we have succeeded in uncovering the first visible steps of this extremely successful visual principle,” says Schoenemann.