Captioned is a nearly intact fossil of Fuxianhuia protensa. The inset shows the fossilized brain in the head of another specimen. The brain structures are visible as dark outlines. (c) Xiaoya Ma; inset: Nicholas Strausfeld

Paleontologists have uncovered the fossil remains of a 3-inch-long extinct arthropod in Yunnan Province, China, dating from the Cambrian period. What makes it particularly special is the fact that it provides an unusual example of preservation of the brain and nervous system, atypical for fossil records this old, but most interestingly it suggests that complex brains evolved much earlier than previously thought.

Embedded in mudstones deposited, the fossilized arthropod – a group of invertebrates that includes insects, spiders and crustaceans – belongs to the species Fuxianhuia protensa; an extinct lineage of arthropods combining an advanced brain anatomy with a primitive body plan. Carbon dating shows its 520 million years-old making it the oldest specimen of its kind.

“No one expected such an advanced brain would have evolved so early in the history of multicellular animals,” said study author Nicholas Strausfeld, a neurobiologist at the University of Arizona, according to statement.

The researchers conclude in their study that the find is “a transformative discovery”, one that might provide the missing link from the evolutionary history of arthropods, while at the same time lead to a resolution of the long standing scientific of about how complex brains evolved, and most importantly how. Some scientists believe that insects evolved from the an ancestor that gave rise to the malacostracans, a group of crustaceans that include crabs and shrimp. Most, however, believe that they were derived from a group of crustaceans called branchiopods, a species that includes include brine shrimp, which have a simpler brain anatomy than malacostracans.

The latter theory however falters in light of this recent find – a simple bodied organism with a complex brain. This suggests that the organism evolved from a previously complex to a more simple architecture instead of the other way around.

“The shape [of the fossilized brain] matches that of a comparable sized modern malacostracan,” the authors write.

“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.”

Findings were published in the journal Nature.