The surprising fossilized brains of ancient sea creatures

More than 500 million years ago, a strange-looking sea creature – Kerygmachela kierkegaardi – roamed the Earth’s oceans. Now, researchers have found more than a dozen fossilized brains and eyes of the ancient ancestor of lobsters, spiders and other modern creepy crawlies.

The newly discovered fossils held a surprise for researchers, however. Until now, many scientists suspected that the common ancestor of vertebrates and arthropods – which would have been an ancestor of K. kierkegaardi, too – had a three-segmented brain, a trait most modern insects share with humans.

But a research team led by Dr. Jakob Vinther of the University of Bristol and Dr. Tae-Yoon S. Park of the Korea Polar Research Institute discovered that this was not the case.

The collection of 15 fossilized brains, discovered in Greenland in 2011 and 2016, show that K. kierkegaardi’s brain had only one segment. That means the three-segmented brains seen in its modern relatives likely evolved later. It also means the shared ancestor of humans and insects probably didn’t have a three-segmented brain, either.

“It has been surmised, based on developmental evidence, that the ancestor of vertebrates and arthropods had a tripartite brain, which is refuted by the fossil evidence presented here,” the researchers wrote in their study, published in the journal Nature Communications.

K. kierkegaardi was about 10 inches long, oval-shaped, with 11 flaps for movement on each side, two long appendages on its head and a long tail. It lived between 521 and 514 million years ago, during the Cambrian explosion. It’s simple “protocerebral” brain may have helped it to survive the time period, when a large number of new animal species began to evolve, the scientists said.

The researchers also believe the fossils demonstrate a middle stage between simpler eye structures and the complex eyes found in modern insects like flies and spiders.

“You can call it a missing link as it contains feature that exists in living creatures, but not in previous fossils,” Vinther told the Daily Mail.

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By Kyla Cathey, Earth.com staff writer

Image credit: Rebecca Gelernter, Near Bird Studios