Are scientific books fake? 525 Million Year Old Fossil Challenges Common Explanation of Brain Evolution

Fossils of a tiny sea creature with a finely preserved nervous system resolve an age-old debate about brain evolution in arthropods, the most species-rich group in the animal kingdom, according to a new study.

Fossils of a tiny sea creature that died more than half a billion years ago could lead to a rewrite of the science textbook on brain evolution.

A new study provides the first detailed description of catenulum of the heartA worm-like animal preserved in the rocks of Yunnan province in southern China. Measuring less than 1.5cm long and first discovered in 1984, the fossil still hides a crucial secret: a carefully preserved nervous system, including the brain. Published in the journal Sciences On Nov. 24, the study was led by Nicholas Strausfeld, Regent Professor in the Department of Neuroscience at the University of Arizona, and Frank Hirth, Senior Lecturer in Evolutionary Neuroscience at King’s College London.

“As far as we know, this is the oldest fossilized brain known to date,” Straussfeld said.

the heart It belongs to an extinct group of animals known as the lobotomy, which abounded at the start of a period known as the Cambrian, when almost all major animal lineages appeared in a very short period of time between 540 million and 500 million years. Lobopods probably moved on the seafloor using several pairs of soft, stubby legs that lacked the joints of their descendants, the euarthropods – a Greek word for “true jointed foot”. The closest living relatives of today’s lobotomy are the velvet worms which live primarily in Australia, New Zealand and South America.

The fossilized Cardiodictyon series was discovered in 1984 among a variety of extinct creatures known as the Chengjian fauna in Yunnan, China. In this photo, the animal’s head is on the right. Credit: Nicholas Straussfeld/University of Arizona

A debate that dates back to the 19th century

fossils the heart It reveals an animal with a segmented trunk that regularly contains nerve structures called ganglia. This is in stark contrast to his head and brain, both of which lack any evidence of segmentation.

“This anatomy was completely unexpected because the heads and brains of modern arthropods, and some of their fossilized ancestors, were considered fragmentary for over a hundred years,” Strausfeld said.

According to the authors, this finding resolves a long and heated debate about the origin and formation of the cephalothorax in arthropods, the world’s most species-rich group in the animal kingdom. Arthropods include insects, crustaceans, spiders and other spiders, as well as some other genera such as centipedes and centipedes.

“Since the 1880s, biologists have noticed the distinctly segmented appearance of the trunk typical of arthropods, and extrapolate this particularly to the head,” Heath said. “This is how the field came to assume that the head is an anterior extension of a segmented torso.”

“But the heart This shows that the early head was not segmented, and neither was the brain, indicating that the brain and trunk nervous system likely developed separately,” Strausfeld said.

Fossil head from the Cardiodictyon series (front right). Purple deposits indicate fossilized brain structures. Credit: Nicholas Straussfeld

Brains don’t freeze

the heart It was part of the fauna of Zhengjiang, a famous fossil site in Yunnan province discovered by paleontologist Xianguang Hu. Soft and delicate lobotomized bodies are well preserved in the fossil record, but different the heart None of them have been examined on the head and brain, possibly because the lobes are usually small. Highlight Share the heart It was a series of triangular saddle-like structures that defined each segment and served as attachment points for the pairs of legs. These have been found in older rocks dating back to the arrival of the Cambrian period.

“This tells us that armored lobopods were probably the oldest arthropods,” Strausfeld said, even before the trilobites, an iconic and diverse group of marine arthropods that went extinct around 250 million years ago.

“Until recently, the common belief was that brains don’t freeze,” Heath said. “So you wouldn’t expect to find a fossil with a preserved brain in the first place. And second, this animal is so small that you wouldn’t even dare to look at it in hopes of finding a brain.

However, work over the past 10 years, largely by Strausfeld, has identified numerous instances of preserved brains in a variety of fossilized arthropods.

Common genetic map to make a brain

In their new study, the authors did not just identify a brain the heart But we also compared it to known fossils and living arthropods, including spiders and centipedes. Combining detailed anatomical studies of fossil lobopods with analyzes of gene expression patterns in their living descendants, they concluded that a common pattern of brain organization has survived from the Cambrian period to the present day.

“By comparing known gene expression patterns in living species, we have identified a common signature for all brains and how they form,” Heath said.

in the heartThree brain domains are associated with a distinct pair of major appendages and one of the three segments of the anterior digestive tract.

Heath added: “We realized that every part of the brain and its associated characteristics are determined by the same genes combined, no matter what species we are looking at.” “It suggested a common genetic blueprint for making a brain.”

Lessons for Vertebrate Brain Development

Hirth and Straussfeld say the principles outlined in their study could apply to other organisms beyond arthropods and their close relatives. This has important implications, they said, when comparing the nervous system of arthropods to that of vertebrates, which exhibit a similar distinctive architecture in which the forebrain and midbrain differ genetically and developmentally from the spinal cord.

Their findings also provide a communication message at a time when the planet is undergoing dramatic changes under the influence of climate change, Strausfeld said.

“At a time when great geological and climatic events were reshaping the planet, simple sea creatures like… the heart It gave rise to the world’s most diverse group of organisms – euarthropods – which eventually spread to all of Earth’s nascent habitats, but are now threatened by short-lived species. “

Reference: “Lobopod Lower Cambrian the heart Determines the Origin of Orthopodic Brains” By Nicholas J. Straussfeld, Xiangwang Hu, Marcel E. Sayre, and Frank Hirth, 24 Nov 2022, Available here. Sciences.
DOI: 10.1126/science.abn6264

The article is co-authored by Xianguang Hou of the Yunnan Key Laboratory of Paleontology at Yunnan University in Kunming, China, and Marcel Sayer, who holds positions at Lund University in Lund, Sweden, and the Macquarie Department of Biological Sciences. In Sydney.

This work was funded by the National Science Foundation, the University of Arizona Regents Fund and the UK Biotechnology and Biological Sciences Research Council.