Palaeontologists say they have uncovered the earliest known complete nervous system, found in an unusual fossilised creature that lived 520 million years ago.
Measuring just three centimetres long, the animal belongs to the megacheirans, a group of clawed marine animals that lived during the Cambrian, a time of riotous biodiversity.
Found in the Chengjiang formation, a treasure trove of fossils in southwestern China's Yunnan province, the museum specimen shows the spine, eyes, brain and ganglia in exquisite detail, the scientists said on Wednesday.
The find was imaged in 3D with a computed tomography (CT) scanner - better known for its use in medicine - to help other researchers compare it against modern and ancient species.
The creature had an elongated, segmented body, attached to which were appendages that enabled it to swim or crawl.
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The head had a long, scissor-like claw, which was probably used for grasping or sensing.
The find provides dating for when the ancestors of today's spiders, scorpions and other members of a family called chelicerates branched off from other arthropods, including crustaceans and millipedes.
"We now know that the megacheirans had central nervous systems very similar to today's horseshoe crabs and scorpions," said lead researcher Nicholas Strausfeld, a professor of neuroscience at the University of Arizona.
"This means the ancestors of spiders and their kin lived side by side with the ancestors of crustaceans in the Lower Cambrian."
The study appears in the journal Nature.
