The brain of a prehistoric worm shaped like a doughnut reveals insights into the evolutionary process of animals during the Cambrian period.
Scientists have discovered a worm’s brain dating back over 500 million years, unveiling the first 3D fossilized nervous system of this ancient creature. The new research was published in the journal Royal Society Open Science on October 5.
The brain tissue (yellow) in a fossilized embryo from the Cambrian period. (Photo: Xi-ping Dong)
In the study, the team of experts detailed the internal anatomy of the fossilized embryo of the species Markuelia humanensis. This creature lived on Earth approximately 500 million years ago, during a time when plants began to emerge on land.
Markuelia humanensis was first discovered in Hunan Province, southern China, according to Philip Donoghue, a member of the research team and a professor of paleobiology at the University of Bristol. Soft tissues are rarely preserved in fossils, especially intricate parts like the nervous system. “Typically, everything is in a flattened fossilized form,” Donoghue stated.
However, the newly discovered fossil of Markuelia humanensis is preserved in three dimensions. “It was preserved in a different way. Essentially, when the specimen began to decay, the microorganisms consuming it turned it to stone and fossilized it. Thus, the specimen became stone before the sediment layer, which protected it from collapsing into a two-dimensional form,” Donoghue explained.
The doughnut-shaped structure of the worm’s brain is similar to that of roundworms and other closely related parasites. “This indicates that the ‘doughnut-shaped’ brain structure developed around 530 million years ago,” Donoghue noted.
The fossil dates back to the early Cambrian period, a time when favorable conditions on Earth set the stage for the largest explosion of animal diversity in history. During this explosion, most major animal groups began to appear in the fossil record.
This new discovery sheds light on the preservation process of brains and nervous tissues in 3D, according to Donoghue. Scientists hope this finding will pave the way for the development of future fossil records and enhance their understanding of animal evolution.
