Many accounts of the early history of ray-finned fishes (actinopterygians) posit that the end-Devonian mass extinction event 359 million years ago had a major influence on their evolution. This episode could have acted as a bottleneck, paring the early diversity of the group to a handful of survivors. Paleontologists have now identified a new genus and species of ray-finned fish — named Palaeoneiros clackorum — that lived in the Appalachian Basin, the eastern United States, during the Late Devonian epoch, approximately 367 million years ago. The species bears an unexpected combination of developed features previously known only in Carboniferous and younger ray-finned fishes.
Palaeoneiros clackorum skull and shoulder girdle. Image credit: Museum of Comparative Zoology, Harvard University / President and Fellows of Harvard College.
The end-Devonian mass extinction, one of the five largest mass extinction events in the history of life on Earth, occurred 359 million years ago.
The event corresponds to a major change in the kinds of fishes populating ancient seas and lakes.
Ray-finned fishes were uncommon before this major crisis, and their success had been linked to new opportunities in the aftermath of the extinction.
After the extinction, in the Carboniferous period, the once rare ray-fins make up a sizeable percentage of fish species.
These new Carboniferous fishes also show features indicating more diverse diets and styles of swimming.
The discovery of Palaeoneiros clackorum, however, suggests that this shift might not have been as stark as a literal reading of the fossil record suggests.
What at first seems like a sudden explosion of diversity instead appears to have had a long — but previously undetected — fuse.
The fossilized remains of Palaeoneiros clackorum were found in Pennsylvania, the United States, over a century ago.
It had previously received little attention because of its size: at only 5.5 cm (2.2 inches) long it was too small to study via conventional means.
However, using CT scanning technology, University of Birmingham paleontologist Sam Giles and colleagues were able to peer inside the fossil’s tiny skull and discover features that showed where Palaeoneiros clackorum fit in the family tree of fishes.
To their surprise, it showed specific internal details not found in Devonian ray-fins, but instead typical of younger species from the Carboniferous.
This would mean the ray-finned fish started to diversify much earlier during the Devonian period, accumulating small but important changes to the internal structure of the head.
These occurred before the outwardly obvious changes appearing during the Carboniferous including new kinds of teeth and highly specialized bodies shaped like everything from eels to angelfish.
“These findings overturn previous assumptions about species diversification around the boundary of the Devonian and Carboniferous periods,” Dr. Giles said.
“It shows a much more complex picture in which, rather than just a handful of survivors, we can see hints of extensive diversification and survival from one period into the other.”
The results appear in the journal Nature Ecology and Evolution.
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S. Giles et al. A Late Devonian actinopterygian suggests high lineage survivorship across the end-Devonian mass extinction. Nat Ecol Evol, published online November 17, 2022; doi: 10.1038/s41559-022-01919-4
Source link: https://www.sci.news/paleontology/palaeoneiros-clackorum-11404.html
