Researchers have announced what might be the oldest example of a brain ever discovered. For 520 million years, the remains of ancient arthropods known as Fuxianhuia have been hiding in the hills of Southern China, interred between layers of ancient mudstone. The body of this long-extinct creature is regarded by researchers as "extremely simple," but evidence from a newly discovered specimen suggests Fuxianhuia may have possessed a surprisingly complex brain.
Over half a billion years ago, early arthropods like Fuxianhuia could be found inhabiting shallow seas near what is now the Yunnan Province in China. These waters receded long ago, but the mineral deposits they left behind have acted like a time capsule, preserving the remains of Fuxianhuia and other Cambrian-era creatures for hundreds of millions of years.
While Fuxianhuia remains have been discovered before, none have retained detailed traces of the creatures' delicate neuroanatomy. But in today's issue of Nature, an international team of researchers report on the fossilized body of a three-inch long Fuxianhuia specimen that possesses such traces, and find its brain to be remarkably advanced.
Fuxianhuia's brain is said to be "tripartite," meaning it comprises three segments. This is similar to what researchers observe in today's insects, malacostracan crustaceans (shrimp, crabs and lobsters, for instance), and chilopoda (like centipedes). According to Nicholas Strausfeld — a neuroscientist renowned for his work on the neural evolution of insects, and co-author of the study — the fact that Fuxianhuia's brain is so similar to that of modern, more neurologically complex creepy crawlies is very surprising:
No one expected such an advanced brain would have evolved so early in the history of multicellular animals... [but] this supports the idea that the ancestor of the insect and malacostracan crustaceans already had a quite complex brain, not a simple one. It also means that branchiopod crustaceans (the kind that live in fresh water or brackish water, and that have much simpler brains) have evolved this simplicity by descent from an ancestor possessing a more complex brain.
The conclusion that branchiopod brains underwent — as Strausfield and his colleagues describe it — "evolutionary reduction and character reversal" provides insight on a longstanding debate over the evolutionary origins of modern day insects. For years, many entomologists have maintained that insects are descended from an ancestor of lesser-brained branchiopods, as opposed to malacostracans; but the discovery of a complex brain in an organism as ancient as Fuxianhuia casts that hypothesis in a less convincing light.
"There have been all sorts of implications why branchiopods shouldn't be the ancestors of insects," explains 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."
The researchers' findings are published in the latest issue of Nature.