Apparently complex brains evolved much earlier than previously thought, as evidenced by a 520-million-year-old fossilized arthropod (the group that comprises crustaceans, arachnids and insects) that is the earliest fossil known to show a brain.
Strausfeld, a Regents Professor in the University of Arizona department of neuroscience explained:
“No one expected such an advanced brain would have evolved so early in the history of multicellular animals. [It] is a very modern brain in an ancient animal.”
The fossil was discovered in the Yunnan Province in China and is about 3 inches long. Researchers travelled to China to study the fossil and took hundreds of pictures of the arthropod. After mapping the brain structure, they realized that it was very similar to modern day animals of the same type leading them to the conclusion that the brain has evolved very little over the course of 500+ million years. They also argue the fossil supports the hypothesis that branchiopod brains evolved from a previously complex to a more simple architecture instead of the other way around.