Complex brains evolved much earlier than previously believed, the discovery of a 520-million-year-old fossilized arthropod has shown.
Embedded in mudstones deposited during the Cambrian period in China's Yunnan Province, the three-inch fossil belongs to the species Fuxianhuia protensa, and represents an extinct lineage of arthropods combining an advanced brain anatomy with a primitive body plan.
"No one expected such an advanced brain would have evolved so early in the history of multicellular animals," says University of Arizona neurobiologist Nicholas Strausfeld.
The discovery casts light on the evolution of insects. While some experts believe that insects evolved from a creature that also gave rise to the malacostracans, a group of crustaceans that includes crabs and shrimp, others point to a different lineage of crustaceans called branchiopods, which include, for example, brine shrimp.
The money's been on branchiopods, as their brain antomy is much simpler is much simpler.
But, says the team, the discovery of a complex brain anatomy in an otherwise primitive organism such as Fuxianhuia makes this scenario unlikely.
"The shape [of the fossilized brain] matches that of a comparable sized modern malacostracan," the authors write in Nature. They 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.
"There have been all sorts of implications why branchiopods shouldn't be the ancestors of insects," says Strausfeld.
"Many of us thought the proof in the pudding would be a fossil that would show a malacostracan-like brain in a creature that lived long before the origin of the branchiopods; and bingo! - this is what this is."