Post Dinosaur Extinction: Fish, Not Mammals, Dominated

Sixty-six million years ago, a massive asteroid struck Mexico's Yucatán Peninsula. As a result, the Earth changed forever, spelling the end of the dinosaurs and ushering in a new age where other animals could flourish. Now new research has revealed that it wasn't mammals who inherited the Earth, but fish.

That's at least according to a study recently published in the Proceedings of the National Academy of Sciences, which details how, following the end of the dinosaurs, ray-finned fish - the most numerous and diverse vertebrates today - enjoyed a significant period of world dominance.

"The diversification of fish had never been tied to any particular event. What we found is that the mass extinction [of dinosaurs] is actually where fish really took off in abundance and variety," Elizabeth Sibert, a paleobiologist at the Scripps Institution of Oceanography, explained in a statement.

"What's neat about what we found is that when the asteroid hit, it completely flipped how the oceans worked," she added. "The extinction changed who the major players were."

The mass extinction of the last dinosaurs, which occurred about 66 million years ago is called the Cretaceous-Paleogene (K/Pg) extinction event. Commonly referred to as the Great Impact, this global disaster is thought to be one of five (arguably six) major mass extinctions that occurred in Earth's past. (Scroll to read on...)

However, for a mass extinction to be called just that, it cannot simply affect one group of animals. According to a great deal of new fossil evidence, the Great Impact not only eliminated the dinosaurs, but also a great deal of mammalian and large aquatic reptile life as well. Even a massive number of mollusk species were not spared, explaining how ray-finned fish could suddenly become so prevalent.

According to the study, Sibert and her colleagues discovered that the number of fish scales and teeth in the fossil record gradually rise soon after the Great Impact, eventually becoming eight times more abundant 24 million years after the extinction event.

"What's amazing," co-invesitgator Richard Norris added, "is how quickly fish double, then triple in relative abundance to sharks (whose presence in the fossil record does not change) after the extinction, suggesting that fish were released from predation or competition by the extinction of other groups of marine life."

"The lineage has been around for hundreds of millions of years," he said, "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."

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