EVOLUTION A tiny marine creature less than 1.5cm long could rewrite the story ofhow brains developed, and help to settle a long-term disagreement.

So claim the scientists who examined 525-million-year-old fossils found in China and discovered what they think is the world’s oldest sample of brain tissue.

The fossils include the remains of a worm-like arthropod, Cardiodictyon catenulum, embedded in rock from Yunnan province in South-Eastern China. With a length of 1.5cm, the fossil was too small to examine with X-rays, so the scientists instead used a special imaging technique that filters light of different wavelengths, mapping the structure of the fossil. The surprise was to find that the brain of the tiny ancient creature that roamed the ocean floor so long ago had been conserved, and that it was comprised of three distinct components separated from the nervous system.

Scientists used to think that early brains would be divided into repeated segments of nerve structures known as ganglia, like the nervous system of the body. But in Cardiodictyon catenulum neither the head nor the brain of the tiny marine creature formed part of the repeated uniform segments. According to the scientists, this indicates that the brain and the body’s nervous system must have developed separately. ■