In the fossil of a 525-million-year-old arthropod, a team of scientists has found the oldest brain ever discovereda finding that could force us to rewrite the texts on how this organ evolved in the animal kingdom.
The fossil, a lobopodian from the Cambrian Period (Cardiodictyon catenulum), had been discovered in the Yunnan province of China in 1984. But only with current technology has it been possible to identify that this ancient 1.5-centimeter animal preserved its system nervous, segmented into a trunk and a brain comprising three head domains.
Following this finding, the team of researchers, led by Nicholas Strausfeld, a professor of neuroscience at the University of Arizona, argued that this is important because it suggests that the brain evolved separately from the nervous system and the head.
Before, however, the scientific consensus dictated that the brain of these animals was composed of ganglia that originated in the ventral nervous system just as in euarthropods, their most widespread descendants on Earth.
A hidden fossilized brain
“To the best of our knowledge, this is the oldest fossilized brain that we know of so far,” Strausfeld said in a statement.
“Until very recently, the common understanding was that ‘brains don’t fossilize,’ so you wouldn’t expect to find a fossil with a preserved brain in the first place. This animal is so small that you wouldn’t even dare to look at it in the hope of finding a brain,” said Frank Hirth, an evolutionary neuroscientist at King’s College London and co-author of the research, published in the journal science magazine.
Cardiodyction’s brain was identified using the chromatic filtering method, which uses a succession of high-resolution images to filter light of different wavelengths to map its internal structure.
The revealed morphology of the lobopodian head and brain was then compared to that of some living arthropods, such as spiders and centipedes. Thus they discovered that this pattern of brain organization has continued from the Cambrian to the present.
“We have identified a common signature of all brains and how they formed. We realized that each brain domain and its corresponding features are specified by the same combination of genes, regardless of the species we studied. This identifies a common genetic blueprint for making a brain,” Hirth added.
Currently, the closest living relatives of the lobopods are the velvet worms, which live mainly in South America, New Zealand and Australia.