Ancient 500-Million-Year-Old Brain Reveals Insights into the Evolution of Early Heads

An ancient brain is telling scientists a bit more about the origins of early heads. Researchers have found a fossil brain more than 500 million years old that reveals a bit more about the process of evolution.

In this case, the scientists looked at the brains of two types of arthropod ancestors-a soft-bodied trilobite and a bizarre creature that resembled a submarine. They found that a hard plate, called the anterior sclerite, and eye-like features at the front of their bodies were connected through nerve traces originating from the front part of the brain, which corresponds with how vision is controlled in modern arthropods.

"The anterior sclerite has been lost in modern arthropods, as it most likely fused with other parts of the head during the evolutionary history of the group," said Javier Ortega-Hernandez, one of the researchers, in a news release. "What we're seeing in these fossils is one of the major transitional steps between soft-bodied worm-like creatures and arthropods with hard exoskeletons and jointed limbs-this is a period of crucial transformation."

The scientists actually found the simple photoreceptors are embedded into the anterior sclerite. The photoreceptors are connected to the front of the fossilized brain, rather like the arrangement in modern arthropods. It's likely that these ancient brains processed information like in today's arthropods, and were critical for interacting with the environment.

Brains and other soft tissues are made out of fatty-like substances, which means that finding them as fossils is extremely rare. This makes understanding the process of brain evolution difficult.

"Heads have become more complex over time," said Ortega-Hernandez. "But what we're seeing here is an answer to the question of how arthropods changed their bodies from soft to hard. It gives us an improved understanding of the origins and complex evolutionary history of this highly successful group."

The findings are published in the journal Current Biology.

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