The exceptional discovery of a 319 million-year-old fossilized brain!

You don’t necessarily have to go to the field to make new discoveries paleontologypaleontology. It may also be wise to examine older collections and reanalyze already known fossils.

It was mined 100 years ago coalcoal This fossil in England fishfish Its age of more than 319 million years has indeed revealed new surprises. It is a passing sound skullskull In the scan, which the researchers accidentally determined appeared to be a fossilized brain.

Detailed mineral casting

Although they were originally soft tissues, they are generally difficult to fossilize the brainthe brain complete and in excellent condition. network of they are nervousthey are nervous the preservation of the skull also allowed for studyanatomyanatomy neural and early developmental stages of ray-finned fishes (actinopterygiansactinopterygians) that is still found in our oceans today. The fish in question,speciesspecies Coccocephalus wildiliving in the oceans at the end CarbonCarbonindeed it is part of this large group of vertebrates.

319-million-year-old fossilized fish sheds light on brain evolution in vertebrates. © Sense of reason

Of course, the brain is no longer in its original state. After rapid burial, soft tissues decomposed slowly and then gradually under low oxygen conditions mineralsminerals (probably pyritepyrite). Therefore, the shape of the organ was preserved, and a relatively detailed structure of the internal part was created. brain cavitybrain cavity Fish. Thus, the skull scan allowed the brain to be digitally and precisely reproduced in 3D without destroying the precious fossil. The results are published in the journal Nature.

The oldest fossil brain of vertebrates

It is the oldest fossilized brain of an animal to date. vertebratevertebrate. Other ancient brainprints have been found, but these are invertebrates. Studies of its structure have shown that the evolution of the vertebrate brain will be more complex than previously thought. This discovery shows the importance of preserving fossil specimens and regularly re-studying them thanks to new technologies developed over time.

Soft tissues are extremely rare in animal fossils. There are more that come from the brain. As for finding them in fossils hundreds of millions of years old, hope seemed forlorn. And yet…

article Jean-Luc GoodeJean-Luc GoodePosted on March 5, 2009

It all started with the rediscovery of four very well-preserved fish fossils from Kansas, part of the collections of the National Museum of History in Paris.MNHNMNHN). These remains belong to a long-extinct species, Sibyrhynchus denisoni, a fish about a foot long, from the group of iniopterygians, cousins ​​of the current chimeraschimeras and close to sharks and rays. Like them, iniopterygians are elasmobranchs, fish characterized by the absence of hard tissues, which makes their fossils fragile.

A fossil found in Kansas. Tomography allows non-destructive analysis. © PNAS

Alain Pradel from MNHN and his colleagues decided to study these skulls using microtomography. x-raysx-raysSimilar to CT medical scanners (for computed tomography) and is able to reconstruct a three-dimensional image from a series of measurements. In one of the skulls, the researchers saw a structure of a special nature, denser than the fossilized cranium, consisting of crystalline calcite.

This skull later went to Grenoble to join the ESRF (European Synchrotron Radiation Facility). This particle accelerator is used as a synchrotron and is available to the international scientific community for numerous analyses. A synchrotron actually produces very fine and extremely powerful X-rays that can be used to test radiation. issueissue in different ways.

The ESRF synchrotron near Grenoble, a kind of giant microscope… © ESRF

The researchers used holotomography. This last process also uses X-rays, but calls it contrastcontrast phase (a technique also known in optical microscopy) highlights otherwise indistinguishable shapes. The interesting internal structure was thus more clearly shown. Its shape and position perfectly matched the brain of this animal.

A very good study that gives hope to others

Scientists were then able to study this nervous system with unexpected precision and described their results in a Pnas study. Three hundred million years later, the images clearly show cerebellumcerebellumthe spinal cordspinal cord, optic lobes and even several nerves, including the optic nerve. The front part of the brain (called the telencephalon) remains invisible. The researchers concluded that this fraction was very small in the living animal, indeed in modern chimeras.

Inopterygian, a cousin of today’s chimeras. © PNAS

The optic lobes are of good size, well matched in size the eyesthe eyes. On the other hand,Inner earInner ear appears to be very small, as previous observations have shown. Apparently, this fish has semicircular canals grouped in only one plane, in this case horizontal. This provision probably only allowed him to collect money actionsactions laterally, not vertically, indicating that Sibyrhynchus denisoni lived on the bottom rather than in the middle of the water.

Ultimately, this analysis reveals a small brain measuring 7 millimeters long and 1.5 wide, a very modest size compared to the skull it was housed in. The team thinks it doesn’t come from a contraction due to its small size fossilizationfossilization as the appendages of the nerves appear in their proper place.

As for why this pattern is so well preserved, the researchers offer an explanation. Chemical analyzes showed that the surface of the brain was covered with phosphate calciumcalcium. This layer could have been deposited by a bacterial film or a chemical process and fossilized the brain.

This remarkable study is also a hope for paleontology. It demonstrates that new analytical techniques can take us deeper into the history of very ancient vertebrates. Other well-preserved fossils may hold secrets waiting to be discovered. tomographytomography good for showing off…

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