It might 520 million years old, but a recent fossil discovery holds the key to a very important step in the evolutionary history of the modern day nervous system. The fossilized remains of a three-centimeter-long distant ancestor of chelicerates, a group that includes spiders and scorpions, marks the world's oldest complete nervous system ever found.
The never-before-seen creature, which was soon identified as a marine arthropod megacheiran (meaning "large claws"), fills in an important link in the evolutionary history of chelicerates. It shows the first time the ancestors of spiders branched off from other arthropods.
"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 from the University of Arizona's Department of Neuroscience. "This means the ancestors of spiders and their kin lived side by side with the ancestors of crustaceans in the Lower Cambrian."
The scientists first theorized that the megacheiran was related to chelicerates by comparing the way the appendages were constructed. Still, that wasn't accurate enough, and it was only by scanning the fossilized nervous system were the experts able to confidently state the relationship between the two.
"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," said co-author on the study Greg Edgecombe.
The researchers are hoping that with more advanced scanning techniques, they can recreate the nervous systems of even older fossils, helping fill in the gaps in our Earth's evolutionary tale.
You can find the full published study in the journal Nature.