A 520 million year old nervous system from a crustacean-like animal was discovered in southern China and is the most well-preserved of its kind.
Researchers have found probably the oldest and most detailed nervous system from a crustacean-like animal that lived more than 500 million years ago. The fossil has been recovered from southern China and is so well-preserved that its individual nerve fibers are still visible, making it the most detailed nervous system ever seen in a fossil of that era.
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Fossil remains are usually recovered in the form of bones or teeth, which are the hardest part of the body. But soft tissues like nerves are very rare to find since they decompose over time. The newly-recovered fossilized nerves system is a surprising discovery in this context.
The nervous system fossil belongs to an ancient animal, called Chengjiangocaris kunmingensis, appeared during the Cambrian explosion, a period when most major animal groups explode onto Earth and changed from single-celled organism to complex multicellular animals in remarkably short period of time. This period yielded an extraordinary number of fossil remains.
C. kunmingensis falls in a group of animals called fuxianhuiids. They are early ancestor of modern arthropods such as insects, spiders and crustaceans and this fossil could help scientists figure out the evolution of nervous systems in modern-day animals.
"This is a unique glimpse into what the ancestral nervous system looked like," said co-author Dr Javier Ortega-Hernández from University of Cambridge's Department of Zoology. "It's the most complete example of a central nervous system from the Cambrian period."
The extinct animal had a broad head and a long body with the legs of varying sizes. By using a find needle and careful handling, researchers were able to clip away the delicate nerve fibers from a rock.
Closer inspection of the fossil revealed that animal contained a chain like series of interconnected nerve tissues called ganglia. This kind of structure containing dozens of nerve fibers is not found in arthropods today expect in certain types of modern worms. Modern arthropods have ganglia but with very limited number of nervers.
“These delicate fibers displayed a highly regular distribution pattern and so we wanted to figure out if they were made of the same material as the ganglia that formed the nerve cord,” said Ortega-Hernández. “Using fluorescence microscopy, we confirmed that the fibers were in fact individual nerves, fossilized as carbon films, offering an unprecedented level of detail. These fossils greatly improve our understanding of how the nervous system evolved.”
Researchers suggest that modern arthropods may have lost huge number of nerves gradually due to simplification.
“Putting all of this together, the new fossil of C. kunmingensis allow us to recognize that the evolution of the nerves system in living arthropods involved the loss of some of these nerves and that their presence in the fossil and the velvet worms is a very ancestral feature,” Ortega-Hernández told Washington Post.
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“We have to bear in mind that each nerve strand is about 10 times thinner than a human hair. So being able to recognize this level of neurological detail is simply amazing."