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A fossilized 525-million-year-old worm found in China has possibly the oldest brain specimen ever discovered. The surprising shape of the brain offers clues about the evolution of arthropods, a group that includes insects, arachnids and crustaceans, and may help solve a mystery that has baffled researchers for more than a century.
ancient creature known as cardiodicion catenulumIt was discovered in 1984 at a site in China’s Yunnan province, along with numerous other fossils, collectively known as the Chengjiang fauna. The worm-like creature belongs to the phylum Lobopodia, a group of extinct, seafloor-dwelling arthropod ancestors with armored shells and short legs that were abundant during the Cambrian period (541 million to 485.4 million years ago).
In a new study published November 24 in the journal Arthropod Evolution (opens in new tab)Another team of scientists reanalyzed the fossilized specimen and found that it was hiding a surprising secret – a preserved nervous system, including the brain.
“As far as we know, this is the oldest fossilized brain we’ve ever known,” said Nicholas Strausfeld, lead author of the study. (opens in new tab)A neurobiologist at the University of Arizona in Tucson, Dr. (opens in new tab).
Related: Perfectly preserved 310-million-year-old fossilized brain found
It took almost 40 years for scientists to discover it. C. catenulumbecause researchers previously believed that any soft tissue in the animal was lost over time.
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“Until recently, the common understanding was: [that] brains don’t fossilize,” says co-author Frank Hirth (opens in new tab)An evolutionary neuroscientist at King’s College London in England, Dr. Due to the fossil’s small size and age, ancient researchers “wouldn’t even dare to look at it in hopes of finding a brain,” he added.
However, recent research on similar fossils dated to recent times has changed this prejudice. To date, primitive fossilized brains have also been found in a 500-million-year-old relative of the penis wolf; an exceptionally well-preserved insect-like creature from about 500 million years ago; a 520-million-year-old “sea monster”; and dozens of three-eyed sea creatures from about 506 million years ago.
Increased arthropod evolution
As surprising as finding the ancient brain was, the researchers were more surprised by the shape and structure of the creature’s skull. The head and brain are both not segmented, meaning they are not divided into multiple parts. But the rest of the fossil’s body is segmented.
“This anatomy was completely unexpected,” Strausfeld said. For over a century, researchers thought that the brains and heads of extinct arthropods were compartmentalized just like those of modern arthropods; Most fossils of other ancient arthropod ancestors also show fragmented heads and brains, he added.
Related: The ancient armored ‘worm’ is the Cambrian ancestor of three main animal groups.
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Even more surprising, C. catenulum He had small clusters of nerves known as ganglia running through his segmented body. As a result of this discovery, the researchers believe that the fragmented brains and heads seen in modern arthropods may have evolved separately from the rest of the nervous system, which was probably fragmented first.
However, the study authors noted: C. catenulumStrausfeld’s fossilized brain still shares some key features with modern arthropod brains, suggesting that the “basic brain blueprint” hasn’t changed too drastically over the past half billion years.
The researchers then want to compare the fossilized brain with the brains of other animal groups to reveal more about how different brains have diversified over time.
