Half-A-Billion-Year-Old Fossilised Brain of Sea Creature Sparks Debate On Evolution Of Brain

The fossil is 1.5 centimeters long and was discovered in 1984.

Fossils of a tiny sea creature that died more than half a billion years ago may force a rewrite of how brains evolved in science textbooks. A new study published in journal Science provides the first detailed description of Cardiodictyon catenulum, a wormlike animal preserved in rocks in China’s southern Yunnan province.

The fossil, which is 1.5 centimeters long and was discovered in 1984, had been hiding a crucial secret until now- a delicately preserved nervous system, including a brain.

“To our knowledge, this is the oldest fossilised brain we know of, so far,” said Nicholas Strausfeld, a Regents Professor in the University of Arizona’s Department of Neuroscience.

Cardiodictyon belonged to an extinct group of animals known as armoured lobopodians, which were abundant early in the Cambrian period, when virtually all major animal lineages appeared in a very short period of time between 540 million and 500 million years ago.

The study further stated that, “Lobopodians likely moved about the sea floor using multiple pairs of soft, stubby legs that lacked the joints of their descendants, the euarthropods – Greek for “real jointed foot.” Today’s closest living relatives of lobopodians are velvet worms that live mainly in Australia, New Zealand and South America.”

Cardiodictyon fossils show an animal with a segmented trunk and repeating arrangements of neural structures known as ganglia. This is in stark contrast to its head and brain, which show no signs of segmentation. 

“This anatomy was completely unexpected because the heads and brains of modern arthropods, and some of their fossilized ancestors, have for over a hundred years been considered as segmented,” Mr Strausfeld continued.

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The discovery, according to the authors, settles a long and contentious debate about the origin and composition of the head in arthropods which include insects, crustaceans, spiders and other arachnids as well as millipedes and centipedes.

Co-author of the study Frank Hirth, said, “From the 1880s, biologists noted the clearly segmented appearance of the trunk typical for arthropods, and basically extrapolated that to the head.”

“But Cardiodictyon shows that the early head wasn’t segmented, nor was its brain, which suggests the brain and the trunk nervous system likely evolved separately,” Mr Strausfeld further added.

According to the authors, their findings also provide a message of continuity at a time when the planet is changing dramatically due to climate change.

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