Researchers have found one of the oldest and most detailed fossils of the central nervous system yet identified, from a crustacean-like animal that lived more than 500 million years ago.
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The fossil, from southern China, has been so well preserved that individual nerves are visible, the first time this level of detail has been observed in a fossil of this age.
The findings, published in the Proceedings of the National Academy of Sciences, are helping researchers understand how the nervous system of arthropods - creepy crawlies with jointed legs - evolved.
Finding any fossilised soft tissue is rare, but this particular find, by researchers in the UK, China and Germany, represents the most detailed example of a preserved nervous system yet discovered.
The animal, called Chengjiangocaris kunmingensis, lived during the Cambrian 'explosion', a period of rapid evolutionary development about half a billion years ago when most major animal groups first appear in the fossil record.
C. kunmingensis belongs to a group of animals called fuxianhuiids, and was an early ancestor of modern arthropods - the diverse group that includes insects, spiders and crustaceans.
"This is a unique glimpse into what the ancestral nervous system looked like," said study co-author Dr Javier Ortega-Hernández, of the University of Cambridge's Department of Zoology.
"It's the most complete example of a central nervous system from the Cambrian period."
Over the past five years, researchers have identified partially-fossilised nervous systems in several different species from the period, but these have mostly been fossilised brains.
And in most of those specimens, the fossils only preserved details of the profile of the brain, meaning the amount of information available has been limited.
C. kunmingensis looked like a sort of crustacean, with a broad, almost heart-shaped head shield, and a long body with pairs of legs of varying sizes.
Through careful preparation of the fossils, which involved chipping away the surrounding rock with a fine needle, the researchers were able to view not only the hard parts of the body, but fossilised soft tissue as well.
The vast majority of fossils we have are mostly bone and other hard body parts such as teeth or exoskeletons. Since the nervous system and soft tissues are essentially made of fatty-like substances, finding them preserved as fossils is extremely rare.
The researchers behind this study first identified a fossilised central nervous system in 2013, but the new material has allowed them to investigate the significance of these finding in much greater depth. ■