Ray-finned fish, the most varied group of creatures with backbones today, were not as severely affected by a global extinction event 360 million years ago as previously believed.
When the Devonian period ended, there was a big change in the kinds of fish that lived in the seas and lakes of that time. Ray-finned fish, which are common in aquariums and on dinner plates, were rare before this major event, and their success was tied to new opportunities that opened up after the extinction.
After the extinction, during the Carboniferous epoch, ray-fins made up a sizable percentage of fish species. These new Carboniferous fish have traits that suggest more varied diets and swimming patterns.
New research published in Nature Ecology and Evolution reveals, however, that this transition may not have been as dramatic as a literal interpretation of the fossil record suggests. What first appears to be a rapid burst of diversity emerges to have had a long, previously unknown fuse.
In the study, a tiny fossilized specimen from the Late Devonian era, some 370 million years ago, was examined by the researchers. The fossil, known as Palaeoneiros clackorum, was discovered more than a century ago in the US state of Pennsylvania. It didn’t get much attention before because it was so small. At only 55 mm long, it was too small to study in the usual way.
However, by peering inside the tiny skull of the fossil using CT scanning technology, the team was able to identify traits that indicated where Palaeoneiros fit in the fish family tree. To their surprise, it had details inside that were not found in ray-fins from the Devonian but were common in younger species from the Carboniferous.
This means that ray-finned fish began to diversify considerably earlier in the Devonian period, accumulating modest but significant alterations to the internal anatomy of the head. These occurred prior to the visible modifications that appeared during the Carboniferous period, such as new types of teeth and highly specialized bodies shaped like everything from eels to angelfish.
“These findings,” according to lead researcher Dr. Sam Giles, “overturn previous assumptions about species diversification around the boundary of the Devonian and Carboniferous periods.
“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.”
These findings imply that additional research into other missed fossils could provide further information about how ray-finned fishes responded to the Devonian extinction. Dr. Giles and her colleagues plan to take a similar technique to additional specimens they’ve discovered in order to better comprehend this key time period.
“The fossil record,” according to the researcher, “provides us with a remarkable opportunity to see how biology responds to major environmental crises.
“And I think we’re getting closer to figuring out how—or if—this spectacularly diverse group’s rise relates to one of the most catastrophic extinctions in Earth’s history.”
Source: 10.1038/s41559-022-01919-4
Image Credit: Museum of Comparative Zoology, Harvard University; © President and Fellows of Harvard College