New Delhi: Over 300 million years ago, a tiny fish died and sank to the bottom of a swamp in northwest England. Today, the fossilised brain and neural tissue of this fish has given scientists a fresh chance to study the brain evolution of similar fossils.
A recent study published on 29 June titled “Neural tissues and chondrostean traits in a Carboniferous actinopterygian” published in the Proceedings of the National Academy of Sciences (PNAS) by paleontologists at the University of Chicago (UChicago) describes the findings as “extraordinary.”
“Soft tissue preservation, in general, is not common in the fossil record, and usually what gets preserved are things like skin or muscles. It’s quite rare for neural tissues to be preserved at all because they decay so quickly. So, the importance of this specimen is that we can now study brain evolution in similar fossils where we only have the bony parts or the infill,” Abigail Caron, PhD, lead author of the study, said in a press release.
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From coal mine to a CT scanner
The fossilised fish was originally discovered in 1888 in a coal mine. It was split into two pieces and for decades those pieces were stored separately in a museum in London before scientists realised they belonged to the same fish — a ray-finned fish known as the Trawdenia which is known to have characteristics similar to modern sturgeons and paddlefish.
“Ray-finned fishes (Actinopterygii) represent over half of extant vertebrate species, but their early evolutionary history is largely unresolved,” the study reads. These fish, named so because their thin fins and bony spine make up for nearly 99 per cent of the existing 30,000 living species of fish.
A key finding of the new study relies on how the brain has been preserved. So far, several fossil brains have appeared too small for the skull around them, however, this particular brain suggests that fossilised skulls could indeed be reliable proxies to estimate the side and shape of the brain when it comes to such fish.
This tiny fish is nothing short of a small celebrity in the world of archeology. Michael Coates, PhD, professor and chair of Organismal Biology and Anatomy at UChicago and senior author of the new research began studying the fish in the 1990s. He wrote a detailed paper about it in 1999 and then brought the fossil for CT scanning in 2018.
With more sophisticated imaging techniques and computational analyses available today, researchers have now been able to study the fossilised neural tissue which fills the inner cavity of the brain. They have also created 3D models from the CT scans to show just how snugly the brain fits the skull.
“This kind of preservation also would only happen in very special circumstances. There are definitely a lot more specimens out there that have reasonably good brain case morphology than there are specimens with good soft tissue preservation. So, that really expands the data set that you can use to study brain evolution across these different fossils,” Caron added.