A team of international researchers led by University of Arizona Regents' Professor Nick Strausfeld and London Natural History Museum's Greg Edgecombe, discovered the earliest known central nervous system in the fossilized remains of a 520-million-year-old creature at the Chengjiang fossil site in southwest China.
The extinct one-inch long species, a marine arthropod known as megacheiran (Greek for large claws'), was scanned and a complete, well-preserved central nervous system was observed.
The findings were published in the current issue of the journal Nature.
"We now know that the megacheirans had central nervous systems very similar to today's horseshoe crabs and scorpions," senior author of the study, Strausfeld, said in an official statement.
The fossil, which belongs to the extinct genus Alalcomenaeus, has an elongated, segmented body and dozen pairs of appendages that enabled the animal to swim or crawl or both. Similar to scorpions, they had scissor-like appendages attached to the head.
"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.
The 520-million-year-old fossil's central nervous system featured three clusters of nerve cells, otherwise known as ganglia, merged together.
"We have now managed to add direct evidence from which segment the brain sends nerves into the great appendage," coauthor Greg Edgecombe from London's Natural History Museum said. "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."
After identifying the species, the researchers set out to solve the group's position in the tree of life.
"Greg plugged these characteristics into a computer-based cladistic analysis to ask, 'where does this fossil appear in a relational tree?'" Strausfeld said. "Our fossil of Alalcomenaeus came out with the modern chelicerates."
"The prominent appendages that gave the megacheirans their name were clearly used for grasping and holding and probably for sensory inputs," Strausfeld said. "The parts of the brain that provide the wiring for where these large appendages arise are very large in this fossil. Based on their location, we can now say that the biting mouthparts in spiders and their relatives evolved from these appendages."
