Complete nervous system discovered preserved in 520-million-year-old fossil in southwest China

Scientists have discovered the earliest known complete nervous system preserved in the fossilised remains of a creature that crawled or swam in the ocean 520 million years ago.

The 3cm-long fossil, found in the Chengjiang formation near Kunming in southwest China, is a distant relative of scorpions and spiders and belongs to an extinct group of marine arthropods known as megacheirans (Greek for “large claws”). Researchers from the University of Arizona’s department of neuroscience and London’s Natural History Museum believe that the ancestors of spiders and scorpions evolved from other arthropods including insects, crustaceans and millipedes, more than half a billion years ago.

“We now know that the megacheirans had central nervous systems very similar to today’s horseshoe crabs and scorpions,” said Professor Nicholas Strausfeld at the University of Arizona, senior author of the study.

“This means the ancestors of spiders and their kin lived side by side with the ancestors of crustaceans in the Lower Cambrian.”

The fossil belongs to the extinct genus Alalcomenaeus and animals in this group had an elongated, segmented body with about a dozen pairs of body appendages enabling the animal to swim or crawl or both.