Mass Extinctions Caused Explosion of Biodiversity in Bony Fish

Although it may see counterintuitive, mass extinctions aren't always a bad thing. Scientists have found that bony fish, the most biodiverse fish group in both salt- and freshwater, achieved their diversity only after mass extinction events during the Permian and Triassic periods.

Today, ray-finned fishes, which belong to the bony fish, include forms that range from eels to tuna to flounders to angler fish. In fact, this group includes about 1,100 species.  Exactly why bony fish prevailed over cartilaginous fish, though, is subject to debate.

The scientists examined the changes in biodiversity among cartilaginous and bony fish during the Permian and Triassic periods around 300 to 200 million years ago. More specifically, they evaluated the scientific literature and collected data on diversity and body size.

The scientists found that cartilaginous fish, the most biodiverse fish group at the time, suffered heavily during an extinction event in the Middle Permian epoch. Ray-finned fish, in contrast, escaped relatively unscathed. Then, an even bigger extinction event occurred close to the Permian-Triassic boundary and wiped out 96 percent of all sea organisms at the time; after, the bony fish diversified heavily.

"Our results indicate that repeated extinction events played a key role in the development of today's fish fauna," said Carlo Romano, one of the researchers in a news release.

In fact, the researchers found that cartilaginous fish never really recovered after they had been heavily decimated at the end of the Permian. In addition, many groups that were still biodiverse in the Permian disappeared completely or became extremely rare during the extinction events of the Permian and the Triassic.

The findings reveal how bony fish manage to be so diverse in the present day. This, in turn, reveals a bit more about the evolution of these species.

The findings are published in the journal Biological Reviews.