Fossilized nerves.

Washington Post reports on an impossible-seeming thing – a fossil that’s not just of hard tissue like teeth and bones (and shells), but that reveals the structures of something as soft as nerves:

Chengjiangocaris kunmingensis wasn’t exactly a beautiful animal: The crustacean-like Cambrian creature had a long, segmented body and an unholy number of legs that it used to scuttle across the ocean floor. But scientists are oohing and ahhing over the ugly arthropod anyway, and for good reason. The nervous system of one 520 million-year-old specimen shows some of the best and most well-preserved nerves ever seen in an animal of that era.

According to a study published Monday in the Proceedings of the National Academy of Sciences, the fossil may be the oldest and most detailed example of a central nervous system yet identified, with even individual nerves — rarely preserved soft tissue — visible enough to study.

“Using a fine needle and a steady hand, they chipped away parts of the rock to reveal the preserved internal features; they only needed a bit of nerve cord sticking out to have a good idea of where to continue excavating in the fossil,” study co-author Javier Ortega-Hernández of the University of Cambridge told The Washington Post in an email. “As usually happens with amazing discoveries, when I first saw the material it took me a bit of time to make sense of what I was looking at. After a little while, however, excitement kicked in after realizing that not only was this an exquisitely preserved nerve cord, but also that it has impossibly thin individual nerves sticking out from it!” he wrote.

Ironically, while the shrimp-like creature’s nervous system has revealed itself to researchers, its legs remain mysterious. In an email to The Post, corresponding author Xi-guang Zhang of Yunnan University explained that despite the unprecedented nerve preservation, the specimen’s legs were too far gone to make an accurate count.

“We know C. kunmingensis has twenty-six limb-bearing trunk segments,” Zhang wrote. Of these, the scientists are fairly certain that the front five segments each had one pair of identical legs.