Advanced scans of the ancient fish Trawdenia planti Neural tissue was revealed that filled almost the entire cranial cavity. The finding provides clues to the early evolution of fin rays and allows fossil skulls to be used to reconstruct brain structure even when the tissues themselves are not preserved.
More than 300 million years ago, a small fish died in an ancient swamp near the village of Trawden in Lancashire, northwest England. Its body sank to the bottom and was buried in a layer of rock among the coalfields of the Burnley area. A rare combination of chemical and geological conditions preserved not only its skeleton but also remnants of the nervous tissue in its brain.
Now, researchers from the University of Chicago have used computed tomography scans to reexamine the fish fossil. Trawdenia plantiThe study, published in the journal Proceedings of the National Academy of Sciences (PNAS), shows that the brain filled most of the interior space of the braincase – a finding that could change the way researchers reconstruct the brains of Ancient fish.
Neural tissues that are almost non-fossilized
Most of thefossils Preserves bones, teeth, scales, or shells. Soft tissues decompose rapidly after death, and only rarely survive the fossilization process. Nervous tissues They are particularly rare in the fossil record because they are delicate and decompose very quickly.
Dr. Abigail Caron, the study's lead author, explained that when soft tissue is preserved, it is usually skin or muscle. Preservation of brain tissue and the membranes of the nervous system is a much more unusual event.
The new scans allowed the researchers to identify traces of the outer and inner membranes of the neural tissue, as well as structures associated with the brain ventricles, where cerebrospinal fluid flowed during the fish's life. The 3D models showed that the neural tissues closely matched the contours of the internal cavity of the skull.
The fish that represents most of the vertebrate world
Trawdenia planti Belonged to the fin rays (Actinopterygii), the group of fish whose fins are supported by thin bony rays. Ray-finned fish are currently the most diverse group of vertebrates: they include almost 99% of the more than 30 living fish species, and about half of all modern vertebrate species.
Despite their enormous success, the early stages ofevolution The origins of the fin rays are still unclear. After the end of the Devonian, there was a rapid diversification of many fish species, but it is difficult to determine how many of the ancient species are related to the groups of animals that exist today.
Professor Michael Coates, the senior author of the study, described the base of the evolutionary tree of fin rays as a kind of dense tangle of branches. Many fossils fromCarboniferous period They combine features that do not allow them to be easily classified as one of the modern fish groups.
A hint of a connection with sturgeons and paddlefish
The structure of the brain Trawdenia planti It includes several features reminiscent of the Chondrostei group, which is currently represented mainly by sturgeons and paddlefish. Among other things, the researchers identified a region in the cerebellum that wraps around the middle part of the brain.
This does not mean that the fossil fish was a direct ancestor of today's sturgeons or paddlefish. The finding suggests that it may represent an early branch close to the evolutionary line from which these groups evolved.
According to Coates, the comparison of the brains depends not only on the relative size of the brain parts, but also on how they were arranged and attached to each other inside the skull. The fossil may record an early stage in the divergence of fish whose modern descendants include sturgeons and paddlefish.
The skull may serve as a template for the brain
One of the most important conclusions of the study is not limited to the particular species studied. Other previously described fish fossils have sometimes shown brain-like structures that were much smaller than the interior of the skull. This has raised questions about whether the shape of the brain can be inferred from the braincase alone.
In the fossil of Trawdenia planti, on the other hand, the neural tissues filled the braincase and conformed to its shape. This suggests that, at least in this type of ancient fish, the internal space of the skull can serve as a fairly reliable indicator of the size and general structure of the brain.
This means that researchers don't have to find fossilized brain tissue in every ancient fish. It will be possible to scan well-preserved skulls, build models of their internal cavity, and use them to reconstruct the shape of the brain. This could greatly expand the number of fossils useful for studying the evolution of the nervous system.
A long way from the coal mine to the scanning lab
The fossil's history is also remarkable. The fish was discovered in 1888 by coal miners in Lancashire. The miners used to collect fossils uncovered during their work, while geologists used plant fossils to identify and map coal seams that could be mined.
The block of rock in which the fish was found had split into two pieces. The two pieces ended up at the Natural History Museum in London and were initially recorded as separate specimens. Only later did Coates realize that they were two halves of the same fossil.
Coates began studying the fish in the 1990s. A detailed description of its skeleton was published in 1999, and the fossil was later scanned in a study published in 2018. Krone continued the work as part of her PhD, using more advanced imaging methods and computer analysis.
The new technology revealed details that were not visible in previous tests. The researchers say that there may be other fossils in museums that have preserved similar markings, but they have not been identified until now because researchers did not have the right tools or did not know what markings to look for.
The finding of Trawdenia planti Demonstrates how a fossil found more than 130 years ago can yield entirely new information thanks to scanning and analysis methods that did not exist at the time of its discovery. It also opens up a way to reexamine fish fossils already in museum collections for evidence of the early evolution of the vertebrate brain.
Questions and Answers
what is Trawdenia planti?
This is an extinct species of small fish from the ray-finned fish group (Actinopterygii), which lived during the Carboniferous period more than 300 million years ago.
What was preserved in the fossil?
Alongside the skeleton and skull, signs of nervous tissue were preserved, including membranes and structures associated with the brain's ventricles. This is a very rare preservation because brain tissue decomposes rapidly after death.
Is the brain itself preserved intact?
Not in the sense of a complete brain with its original biological composition. The fossilization process preserved the shape and traces of neural tissues after they were replaced or filled with minerals.
Why is it important that the brain filled the brain box?
The correspondence between the brain and the internal cavity of the skull indicates that the shape of the braincase can be used to reconstruct the size and general structure of the brain even in fossils where the soft tissues have not been preserved.
What is the relationship between the fish and sturgeons and paddlefish?
Its brain structure includes features reminiscent of fish from the Chondrostei group, represented today by sturgeons and paddlefish. It is not necessarily their direct ancestor, but may be close to an early branch of the group.
Why is the fossil being studied only now, even though it was discovered in the 19th century?
The fossil has been studied in the past, but new tomography and computer analysis methods have made it possible to identify delicate structures within the skull that could not be seen with previous technologies.
The scientific article
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