The fossil of a tiny sea creature that died more than half a billion years ago can be challenging. rewrite the story of how the brain evolved. a study on cardiodicion catenulumA worm-shaped animal preserved in rocks in southern China’s Yunnan province has opened up a hitherto unknown panorama. It is only 1.5 centimeters long and was first discovered in 1984. The fossil was hiding a very important secret: a carefully preserved nervous system, including the brain.
“As far as we know, this It is the oldest fossilized brain we know of so far.Nicholas Strausfeld of the University of Arizona, who co-authored the study with Frank Hirth of King’s College London, published the research in the journal Science. Science.
this cardiodiction belonged to a group of known extinct animals. As armored lobopodia, abundant in the early CambrianBetween 540 and 500 million years ago, nearly all major animal lineages emerged in an extremely short time. Lobopodians probably moved on the bottom of the sea. Its closest relatives living today are the velvet worms, which mostly live in Australia, New Zealand and South America.
A debate dating back to 1800
fossils cardiodiction to show an animal with a segmented body with repeating arrangements of neural structures known as ganglia. This is in stark contrast to his head and brain, both of which lack evidence of segmentation.
“This anatomy was completely unexpected.“Because the heads and brains of modern arthropods and some of their fossilized ancestors have been considered compartmentalized for over a hundred years.”
According to the authors, this finding resolves a long and heated debate about the origin and composition of the head of arthropods, the world’s most species-rich group in the animal kingdom. Arthropods include insects, crustaceans, spiders, and other arachnids, as well as several other lineages such as centipedes and centipedes.
“Since the 1880s, biologists have noticed the distinctively segmented appearance of the typical arthropod body and have basically guessed it to the head,” said Hirth. “Well, The head was assumed to be the anterior extension of a segmented body.“, added.
“Aim.audiodiction indicates that your early head and brain were not compartmentalized, which The brain and central nervous system probably evolved separately.said Strausfeld.
fossilized brains
The most prominent episodes cardiodiction these were a series of triangular saddle-shaped structures that defined each segment and served as attachment points for pairs of legs.
“This tells us that armored lobopods may have been the first arthropods.” Strausfeld explained that it even predates trilobites, the iconic and diverse group of marine arthropods that went extinct about 250 million years ago.
“Until recently, the general consensus was that ‘brains don’t fossilize,’” said Hirth. “Therefore, first of all, you wouldn’t expect to find a preserved brain fossil. Second, this animal is so small that no one would dare to study it in hopes of finding a brain.”
However, the work of the last 10 years, much of which has been done by Strausfeld, identified several cases of preserved brains in various fossilized arthropods.
A common genetic blueprint for making a brain
In their new study, the authors didn’t just describe his brain. cardiodiction, but also compared it with known fossils and living arthropods, including spiders and centipedes. After combining detailed anatomical studies of Lobopodian fossils with analyzes of gene expression patterns in their living descendants, The researchers concluded that a common pattern of brain organization has been preserved from the Cambrian to the present.
“By comparing known gene expression patterns in living species, we identified a common signature of all brains and how they form,” said Hirth.
Inside cardiodictionEach of the three brain areas is associated with a characteristic pair of head appendages and one of the three parts of the anterior digestive tract.
“We noticed that each brain area and its corresponding traits were determined by the same combination of genes, regardless of the species we examined,” added Hirth. “This revealed a common genetic blueprint for making brains.”
Lessons for the evolution of the vertebrate brain
Hirth and Strausfeld argue that the principles described in their work It probably applies to other creatures beyond arthropods and their close relatives.. They noted that the nervous system of arthropods has important implications when comparing the forebrain and midbrain to that of vertebrates, which similarly exhibit a different architecture, being genetically and evolutionarily different from the spinal cord.
Strausfeld said their findings also offer a message of continuity at a time when the planet is changing dramatically under the impact of climate change.
“At a time when major geological and climatic events are reshaping the planet, simple marine animals cardiodiction It gave rise to the world’s most diverse group of organisms, the exarthropods, which eventually spread to all of Earth’s emerging habitats but are now threatened by our own short-lived species.”
Reference work: https://www.science.org/doi/10.1126/science.abn6264
…….
Contact address of the environment department: [email protected]