November 17 () –
Stingray-finned fish, currently the most diverse group of animals with a backbone, they were not as affected by a mass extinction event 360 million years ago as previously thought.
This is the conclusion of a new study published in the journal ‘Nature Ecology and Evolution’.
The extinction event that ended the Devonian period corresponds to a major change in the types of fish that populated the ancient seas and lakes. The staple of the aquarium and the table, ray-finned fish were rare before this great crisis, and its success has been linked to new opportunities after extinction.
After the extinction, in a period called the Carboniferous, the previously rare stingray fish make up a considerable percentage of the fish species. These new Carboniferous fish they also display traits that indicate more diverse diets and swimming styles.
However, the study suggests that this change might not have been as marked as a literal reading of the fossil record suggests. What at first glance seems like a sudden explosion of diversity seems to have had a long – but so far undetected – denouement.
In the study, the researchers analyzed a tiny fossil specimen from the late Devonian period, about 370 million years ago. The fossil, named ‘Palaeoneiros clackorum’, was found in the US state of Pennsylvania more than a century ago. Until then, it had not received much attention due to its size: at only 55 millimeters in length it was too small to study by conventional means.
However, thanks to CT scanning technology, the team was able to peek inside the fossil’s tiny skull and discover features that showed the Palaeoneiros’ place in the fish family tree. To his surprise, it showed specific internal details not found in Devonian stingray fins, rather they are typical of the younger Carboniferous species.
This would mean that ray-finned fish began to diversify much earlier during the Devonian, accumulating small but important changes to the internal structure of the head. These changes occurred before the external changes evident during the Carboniferous appeared, such as new types of teeth and highly specialized bodies with shapes ranging from eel to angelfish.
Lead researcher Dr Sam Giles said: “These findings overturn previous assumptions about species diversification around the Devonian-Carboniferous boundary. It paints a much more complex picture in which, rather than just one handful of survivors we can see signs of broad diversification and survival from one period to the next,” Add.
These results suggest that further investigation of other neglected fossils could provide further clues about how ray-finned fishes responded to extinction in the late Devonian.
Giles and his colleagues hope to apply a similar approach to other specimens they have identified, in order to better understand this critical time period.
“The fossil record offers us an extraordinary opportunity to see how biology responds to major environmental crises,” explains Dr Giles. “And I think we are getting closer to finding out how – or if – the rise of this spectacularly diverse is related to one of the most catastrophic extinctions in Earth’s history.
