Fossilized Nervous System of Never-before-seen Ancient Creature 'Exquisitely Preserved'

A 520-million-year-old fossil of a never-before-seen creature has paleontologists excited because the creature's complete nervous system is also entombed in the rock, the earliest known example from a group of creatures called megacheirans, ancient ancestors of spiders and scorpions.

Writing in the journal Nature, the University of Arizona team that described the fossil said it was "exquisitely preserved" and that the creature either crawled or swam through the oceans half a billion years ago.

"We now know that the megacheirans had central nervous systems very similar to today's horseshoe crabs and scorpions," said the senior author of the study, Nicholas Strausfeld. "This means the ancestors of spiders and their kin lived side by side with the ancestors of crustaceans in the Lower Cambrian."

The fossil was unearthed in the famous Chengjiang formation near Kunming in southwest China, a site of many revelatory fossil finds.

Megacheirans are called so because of a pair of long, scissor-like appendages on their heads. Paleontologists call the feature the "great appendage."

The extraordinary preservation of the fossil gives researchers new insights into the inner workings of the ancient creatures.

"We have now managed to add direct evidence from which segment the brain sends nerves into the great appendage. It's the second one, the same as in the fangs, or chelicerae," said study co-author Greg Edgecombe For the first time we can analyze how the segments of these fossil arthropods line up with each other the same way as we do with living species -- using their nervous systems."

The fossil appears to have similarities with hallmarks in the brains of scorpions and spiders, the researchers said.

"Three clusters of nerve cells known as ganglia fused together as a brain also fused with some of the animal's body ganglia. This differs from crustaceans where ganglia are further apart and connected by long nerves, like the rungs of a rope ladder," the researchers wrote in a statement. "Other diagnostic features include the forward position of the gut opening in the brain and the arrangement of optic centers outside and inside the brain supplied by two pairs of eyes, just like in horseshoe crabs."

Earlier this year, the same researchers published work detailing the fossilized brain of an ancient creature similar to a modern crustacean.

"Our new find is exciting because it shows that mandibulates (to which crustaceans belong) and chelicerates were already present as two distinct evolutionary trajectories 520 million years ago, which means their common ancestor must have existed much deeper in time," Strausfeld said. "We expect to find fossils of animals that have persisted from more ancient times, and I'm hopeful we will one day find the ancestral type of both the mandibulate and chelicerate nervous system ground patterns. They had to come from somewhere. Now the search is on."