A new study has revealed that more than 70% of sharks died roughly 19 million years ago, but no one knows why.
Earth scientists from Yale University and College of the Atlantic recently made the discovery, saying it happened during a period in history where there were 10 times the amount of sharks in the ocean than today.
"We happened upon this extinction almost by accident," Elizabeth Sibert with Yale University said in a news release. "What we found, though, was this sudden drop-off in shark abundance around 19 million years ago, and we knew we had to investigate further."
"I study microfossil fish teeth and shark scales in deep-sea sediments, and we decided to generate an 85-million-year-long record of fish and shark abundance, just to get a sense of what the normal variability of that population looked like in the long term," Sibert continued.
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According to Sibert, the massive "die-off" was twice the level of extinction that sharks experienced during the Cretaceous-Paleogene mass extinction. The event was 66 million years ago and wiped out three-quarters of the plant and animal species on Earth.
Scientists said there was no "climate calamity" or "ecosystem disruption" 19 million years ago, adding to the mystery.
"This interval isn't known for any major changes in Earth's history," Sibert continued. "Yet it completely transformed the nature of what it means to be a predator living in the open ocean."
Researchers pointed out that past discoveries of extinction events have led to new research to learn the origins of the extinction. They said it’s possible that the shark die-off may have altered the current shark population’s habitat preference to avoid the open ocean.
Additional research might be needed help to explain why shark populations never rebounded after the die-off 19 million years ago.
This story was reported from Los Angeles.