500-million-year-old fossilized brain has totally changed our minds

Fossils of just about everything have been unearthed, from ancient feathers to entire dinosaur skeletons preserved in opal, but there is one thing nobody thought could survive hundreds of thousands of years — until now.

Brain matter from a Cambrian arthropod that crawled around 500 million years ago has proven many paleontologists wrong about brain decay being inevitable. Previous research suggests that no matter what it may be protected by, soft neural matter will break down long before fossilization can even start. Minds have suddenly been changed. Alalcomenaeus may have been a tiny creature, but its exoskeleton was tough enough to ward off decomposition.

There was an “unusual abundance of exceptionally preserved [animal and plant life] in Cambrian deposits, which capture details of the non-biomineralized anatomy that would normally be lost to decay, even under other pathways for exceptional preservation,” according to the Harvard research team who made the find in Utah and recently published a study in Proceedings of the Royal Society B.

This is kind of a big deal when humans have known about the brain’s tendency to break down after death for so long that even the ancient Egyptians knew it had to go during the mummification process. There was no point in trying to preserve it like some other organs (never mind that the heart was believed to be the epicenter of thinking back then). It seems that an organ that can’t be mummified would never stay intact long enough to fossilize, but what appeared to be a stain on the Alalcomenaeus fossil that was recently dug up was found to be its brain.

An Alalcomenaeus brain doesn’t exactly look like a human brain. It really has no resemblance to a human brain at all, but is more of a central nervous system that mirrors those of many extant arthropods, with an elongated brain structure that runs from its head to its upper back. Neural tissue connects to the creature’s four eyes and four pairs of segmented nerves. More nerves from the brain extend all the way down its back.

This system of nerves appeared as a dark stain on the specimen, but because neural tissue is rich in carbon, the traces of carbon in that stain gave it away as a brain frozen in time. The connection of this structure to the Alalcomenaeus’ eyes signified optic nerves, further proof that it really was nerve tissue. That evidently wasn’t the only soft tissue that has been fossilized in this species. Part of another specimen’s gut was also observed, and guts are infamous for succumbing to decay.

While there have been doubts about these stains being the leftovers of decay-related microbes that had long since devoured any soft tissue, the stain in the recently studied Alalcomenaeus specimen was thought of as too precise and symmetrical to be another blob of bacteria.

“Our study represents, to our knowledge, the first case of consistent anatomical organization of the exceptionally preserved CNS of [Alalcomenaeus],” the researchers said, adding that paleontologists need “to gravitate away from the preconception that nervous tissues are too labile to become fossilized, as evidence keeps accumulating that neurological preservation is possible through [certain conditions].”

Could it be possible that a fossilized human brain is buried somewhere deep beneath the surface? Unlikely, but if accidentally mummified brains have been found, you never know.

(via Proceedings of the Royal Society B)