500-million-year-old fossil offers insights into the evolution of brains
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Until recently, scientists believed brains don’t fossilize. However the work of an international team of researchers has not only challenged that idea, but also uncovered secrets that went against common research into how brains evolved.
The process that freezes structures of ancient life forms in time requires specific conditions that are much more likely to capture hard structures like bone, rather than soft tissue.
That is especially the case for brain matter.
Sometimes, however, there are exceptions, such as the fossil discovered that is between 500 million and 540 million years old.
Over the last decade, University of Arizona professor Nicholas Strausfeld has identified multiple cases of preserved brains in multiple arthropod fossils. Modern arthropods include spiders, insects and crustaceans.
Hear Nicholas Strausfeld on The Show with host Mark Brodie
He took pictures of the fossils, and used Photoshop to remove specific light spectrums, until he saw structures of a nervous system in the visible red wavelength. This offered clues into how they were preserved.
“The nervous system had a high concentration of iron containing proteins. And that’s what probably helped the preservation of the nervous system," Strausfeld said.
In 1984, fossils that were barely half an inch long of the species Cardiodictyon Catenulum were discovered in Yunnan, China. It was a part of a famous deposit of fossils called the Chengjiang fauna.
That species is part of an extinct group of animals called armored lobopodians with velvet worms being the closest living relatives.
Frank Hirth with King's College London researches evolutionary neuroscience.
“The significance of these lobopodia is that for a long time they have been considered as ancestral to all arthropods," Hirth said.
Scientists believe that these lobopodia were very common during the Cambrian period.
“The trouble is they are terribly small, very small indeed. And I was in Kunming in the laboratory in 2018 and I was looking at one particular species, And I noticed in some specimens, they showed some very interesting structures that they must be neural," Strausfeld said.
The fossilized brain was not only notable for being identified but also offers clues into brain blueprints.
“One of the most important discoveries is that the ancestral situation was nonsegmented. That, of course, is unprecedented and also unexpected. Which means that those brains that we see nowadays may not be segmented either. And we may have to revisit our interpretation of the Arthropodhead and brain," Hirth said.
That segmentation is key. Because all life has lineages dating back to the Cambrian era, this offers insight in how brains evolved.
“It contradicts the established idea since 1882, that the head of insects, and crustaceans, and spiders, etc. were specifically segmented. There’s been discussions about this for yonks, you know real rouse amongst scientists. It was very cantankerous very often in literature," Strausfeld said.
Strausfeld says human brains are segmented, and divided into three major parts, the forebrain, midbrain and hindbrain. They are distinct in the terms of function and development history.
Brains of modern insects show similar brain segmentation to vertebrates, and it’s unknown where the similarities started.
“So, this suggests that these domains that people have been calling segments are very ancient. And that the idea of segmentation has only sort of been imposed intellectually because people see these later examples of this evolutionary process which shows these very, very strict divisions," Strausfeld said.
Frank Hirth in London said that they have been able to identify a common signature of how all brains formed by examining genes of living organisms and comparing them to the fossils.
And even though we are looking at the brains of animals relating to arthropods, there could be some implications for vertebrate brain development.
“And it turns out there is, if you like, a ground pattern required for brain formation. And that knowledge we can now extrapolate to other species including Chordates and vertebrates like us to ask if that similar ground pattern applies there," Hirth said.
The UA’s Nicholas Strausfeld says studying genes of our old ancestors could offer major insights.
“If we can find that there’s very, close similarities, then I think the case is strengthened that these are ancient, ancient rules of the game that must have occurred in some ancestral group before the divide occurred between the vertebrate and the invertebrate lineages," he said.
And it goes beyond that; Strausfeld says there is more than just knowledge of what was when it comes to studying the evolution of bug brains.
“Biologists in particular now are very urgent to find how life began because we’re doing such damage to how life is at the present," Strausfeld said. "So the more we can inform the public, that this is so important to understand what life is, and how fragile it is, and how amazing it is that survived I mean really catastrophic events over the last half a billion years, maybe, maybe a few people might be persuaded to take better care of life as it is on this planet."
