Sharks Nearly Went the Approach of the Dinosaurs 19 Million Years In the past

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These declines in relative and absolute shark abundance counsel that one thing occurred to shark populations about 19 million years in the past, Dr. Sibert concluded.

However there was nonetheless the query of whether or not a real extinction occurred, she mentioned. “We wished to know if the sharks went extinct, or if they only grew to become much less outstanding.”

To check the concept of an extinction, Dr. Sibert recruited Leah D. Rubin, a marine scientist then on the Faculty of the Atlantic in Maine. Collectively, they developed a framework to establish distinct teams of denticles.

The researchers settled on 19 denticle traits — reminiscent of their form and the orientation of their ridges. Dr. Sibert and Ms. Rubin sorted roughly 1,300 denticles into 88 teams. These teams don’t correspond precisely to shark species, however seeing extra teams is an indicator {that a} shark inhabitants is extra numerous, the researchers proposed.

Of the 88 denticle teams initially current earlier than 19 million years in the past, solely 9 persevered afterward. The discount in shark variety means that they skilled an extinction round that point, Dr. Sibert and Ms. Rubin concluded. In reality, this occasion was most likely much more cataclysmic to sharks than the dinosaur-killing asteroid impression that occurred 66 million years in the past, they mentioned.

“There have been only a small fraction that survived into this post-extinction world,” Dr. Sibert mentioned.

The consequences of this extinction had been seemingly felt world wide. The constant outcomes from the 2 sediment cores — separated by 1000’s of miles — counsel that this was really a “international occasion,” two paleontologists, Catalina Pimiento of the College of Zurich and Nicholas D. Pyenson of the Smithsonian Establishment, wrote in a perspective article that accompanied the examine in Science.

To date, the reason for this die-off stays unknown. There have been no important climatic adjustments within the early Miocene, and there’s no proof of an asteroid impression round that point. “We don’t know,” mentioned Dr. Sibert.

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