Home Science Fossils of a tiny sea creature solve century-old debate over brain evolution in arthropods

Fossils of a tiny sea creature solve century-old debate over brain evolution in arthropods

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Fossils of tiny sea creatures that died more than 500 million years ago may force a rewrite of science textbooks on how the brain evolved.

A study published in Science – led by Nicholas Strausfeld, Regent Professor of Neuroscience, University of Arizona, and Frank Hirth, Reader of Evolutionary Neuroscience, King’s College London – provides the first detailed explanation. cardiodiction catenary, a worm-like animal preserved in rocks in Yunnan, southern China. First discovered in 1984, the mere 0.5-inch (1.5-centimeter) long fossil hides a big secret to this day. It’s a delicately preserved nervous system that includes the brain.

As far as we know, this is the oldest fossilized brain we know of. ”

Nicholas Strausfeld, Executive Professor, Department of Neuroscience, University of Arizona

aerobic exercise These are extinct animals known as armored phylopods that were abundant during the early Cambrian and from which nearly all major animal lineages emerged in a very short period of time, 540-500 million years ago. belonged to the group of Lobopodians probably used the multiple pairs of soft, stocky legs that lacked the joints of their descendants, arthropods—Greek for “real articulated feet”—to move around the ocean floor. Currently, the closest living relatives of lobopodia are the velvet worms, which live mainly in Australia, New Zealand, and South America.

Arguments dating back to the 1800s

Fossil of aerobic exercise reveal animals with segmented trunks with repeating arrays of neural structures known as ganglia. This is in stark contrast to the head and brain, both of which have no evidence of somites.

“This anatomy was totally unexpected, as the heads and brains of modern arthropods, and some of their fossilized ancestors, have been thought to be segmented for over 100 years.” says Strausfeld.

According to the authors, the discovery settles a long-heated debate about the origin and composition of the head of arthropods, the world’s most species-rich group of animal kingdoms. , crustaceans, spiders, and other arachnids, as well as other strains such as millipedes and centipedes.

“Since the 1880s, biologists have focused on the distinctly segmented appearance of the torso typical of arthropods and essentially extrapolated it to the head,” Hirth said. “This is how the field arrived at postulating that the head is an anterior extension of the segmented trunk.”

“However aerobic exercise “It shows that neither the early head nor the brain was segmented, suggesting that the brain and trunk nervous system likely evolved separately,” said Strausfeld.

the brain fossilizes

aerobic exercise It was part of the Chengjiang Fauna, a famous deposit of fossils in Yunnan discovered by paleontologist Xianguang Hou. Robopodians’ soft, delicate bodies are well preserved in the fossil record, aerobic exercise The heads and brains have never been examined, perhaps because lobopodians are generally small.the most prominent part of aerobic exercise It was a series of triangular saddle-shaped structures that defined each segment and served as attachment points for pairs of legs. They were found in even older rocks dating back to the advent of the Cambrian period.

It predates the trilobites, an iconic and diverse group of marine arthropods that went extinct some 250 million years ago, Strausfeld said.

“Until very recently, the general understanding was that the brain doesn’t fossilize,” Haas says. “So you wouldn’t expect to find a fossil with a preserved brain in the first place. And secondly, this animal is so small you wouldn’t even dare to look at it in hopes of finding a brain.”

However, much of the research in the last decade was done by Strausfeld, who identified several cases of preserved brains in various fossilized arthropods.

General genetic ground plan for building the brain

In their new study, the authors not only identified the brain, aerobic exercise As well as comparing it to known fossils and those of living arthropods, including spiders and centipedes. Combining detailed anatomical studies of lobopodian fossils with analysis of gene expression patterns in living offspring, they conclude that a shared blueprint of brain tissue has been maintained from the Cambrian to the present day. attached.

“By comparing known gene expression patterns in living species, we identified common signatures in all brains and how they are formed,” Hirth said.

of aerobic exercisethe three brain domains are each associated with a characteristic pair of head appendages and one of the three parts of the anterior digestive system.

“We found that each brain domain and its corresponding function was specified by the same combinatorial genes, regardless of the species we examined,” Hirth added. “This suggests a general genetic master plan for building the brain.”

Evolutionary lessons of the vertebrate brain

Hirth and Strausfeld say the principles described in their study probably apply to other organisms besides arthropods and their relatives. This has important implications when comparing the arthropod nervous system to the vertebrate nervous system, in which the forebrain and midbrain are genetically and developmentally distinct from the spinal cord. , which shows a similar well-defined structure.

Strausfeld said their findings also provide a message of continuity at a time when the Earth is changing dramatically under the effects of climate change.

“When major geological and climatic events were reshaping the Earth, simple marine animals such as aerobic exercise Produced the world’s most diverse group of organisms, the true arthropods, which eventually spread to all emerging habitats on Earth, but are now threatened by our own temporary species. I’m here. ”

Paper “Lower Cambrian Robopodian” aerobic exercise Resolves the Origin of Euarthropod Brains” was co-authored by Xianguang Hou, Yunnan Key Institute of Paleontology, Yunnan University, Kunming, China, and Marcel Sayre, Appointed to Lund University and Department of Biology, Lund, Sweden . Majored in Science at Macquarie University, Sydney.

Funding for this work was provided by the National Science Foundation, the University of Arizona Regent’s Fund, and the UK Biotechnology and Biological Sciences Research Council.

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