Scientists say that the recently discovered 520 million year old insect brain, the oldest brain ever discovered in an arthropod, is surprisingly complex for its age, and may be the earliest example on record of a modern brain structure.

Hailed as a "transformative discovery," researchers said that the 3-inch-long fossilized extinct arthropod found in Yunnan Province, China, shows that insects evolved to have complex brains significantly earlier than previously thought.

Researchers said that the fossilized brain, which looks very similar to brains of modern insects, may provide a missing link that offers new insight on the evolutionary history of arthropods, a group of invertebrates that includes insects, spiders and crustaceans.

"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.

Encased in mudstones deposited during the Cambrian period 520 million years ago, the fossil belongs to the species Fuxianhuia protensa.

Researchers say that the latest discovery, which was reported in the journal Nature, represents the oldest specimen of its kind to combine an advanced brain anatomy with a primitive body, suggesting that insect brains may have evolved from an initial complex structure to a simpler one instead of the other way around.

Experts say that the finding promises to revolutionize research into how insects evolved through time.

They explained that up until now, research on insects has been divided into two camps. While some researchers believe that insects evolved from the same ancestor that gave rise to malacostracans, a group of crustaceans that include crabs and shrimp, the majority of scientists 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.

However, researchers from the latest study say that the new finding shows that insects did in fact evolve from creatures that already possessed complex brains.