Dinosaur Mass Extinction Caused the Rise of Fish Biodiversity

It turns out that the mass extinction event that killed off the dinosaurs may have made the way for fish. Researchers have discovered that the world's most numerous and diverse vertebrates, ray-finned fish, began their dominance 66 million years ago after the mass extinction event.

A total of 99 percent of all fish species in the world are classified as ray-finned fish. They are defined as species with bony skeletal structures and have teeth that are well preserved in deep ocean mud. In contrast, sharks have cartilaginous skeletons and are presented by both teeth and mineralized scales in marine sediments.

In this latest study, the researchers examined fossilized teeth and shark scales in cores from numerous ocean basins. This revealed that the number of sharks remained steady before and after the extinction event. However, the ratio of ray-finned fish teeth to shark teeth and scales gradually rose, first double and then becoming eight times more abundant about 24 million years after the extinction event that killed the dinosaurs.

"The diversification of fish had never been tied to any particular event," said Elizabeth Sibert, one of the researchers, in a news release. "What we found is the mass extinction is actually where fish really took off in abundance and variety. What's neat about what we found is that when the asteroid hit, it completely flipped how the oceans worked. The extinction changed who the major players were."

Large marine reptiles disappeared during the mass extinction, as did ammonites. These species had been either predators of ray-finned fish or competitors with them for resources.

"Mammals evolved 250 million years ago but didn't become really important until after the mass extinction," said Sibert. "Ray-finned fishes have the same kind of story. The lineage has been around for hundreds of millions of years, but without the mass extinction event 66 million years ago, it is very likely that the oceans wouldn't be dominated by the fish we see today."

The findings are published in the journal Proceedings of the National Academy of Sciences.

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