Scientists have uncovered one of the rarest animal fossils ever, unearthing a delicate fossil of soft tissues and nerve fibers from one of the oldest specimens of nervous systems that has ever been found.

This fossil was discovered in Southern China and is estimated to be 520 million years old, belonging to an ancient crustacean. Scientists say that this specimen is so well preserved that each of its individual nerves are prominent, making this the first of fossil of this age to possess this level of detail.

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This prehistoric crustacean is known as the Chengjiangocaris kunmingensis that lived during the Cambrian explosion some 500 million years ago. This period is where rapid evolutionary growth ensued as animals diversified and emerged into different groups and species which is now seen in fossil records. The C. kunmingensis is included in a group of animals known as fuxianhuiids where it was an early ancestor of modern arthropods like crustaceans, spiders and insects.

According to co-author of the study, Javier Ortega-Hernández of the University of Cambridge, this fossil is the most complete sample of a nervous system that originates from the Cambrian period that offers the most unprecedented level of detail.

A team of international researchers first identified this fossilized central nervous system in 2013 where they discovered new material for this study, allowing them to further investigate, revealing that the C. kunmingensis is a crustacean with broad, heart shaped head shield and a long body that is lined with different sizes of pairs of legs.

Scientists were able to carefully extract the animal's body from the surrounding rock with a special, fine needle where they were able to view its fossilized soft tissues as well, resembling a string of beads known as ganglia, that are brain-like interconnected tissues. This is equivalent to spinal cords in vertebrate animals like mammals, primates, fish, birds.

Similar to modern day arthropods, the C. kunmingensis also had a nerve cord that is similar to spinal cords of vertebrates that runs across its body. Each of the ganglia is responsible for controlling a pair of legs. The team also found dozens of fibers that are measuring 1/5,000 of a millimeter in length.

Ortega-Hernández revealed that these highly intricate fibers show an evenly distributed pattern as researchers examined if the fibers were made from the same material as the ganglia. Using fluorescent microscopy, they confirmed that the fibers were in fact, separate nerves that are fossilized into carbon films.

Researchers also note that the C. kunmingensis specimen also shows some similarities with the nervous system of onychophorans or velvet worms. However, these nerve fibers disappeared in modern arthropods, indicating how the nervous system evolved into a simpler structure.

Ortega-Hernández says that this new study offers a better understanding about the evolution of early animals during the Cambrian period, as more fossils of early nervous systems are uncovered.

This new study will be published in the journal, Proceedings of the National Academy of Sciences.