A new study finds that a mysterious event nearly 19 million years ago wiped out nearly an entire population of sharks. The scientists behind the new research say that studying shark teeth buried in deep-sea sediments has shown that the current diversity among sharks is only a small remnant of the much larger diversity that existed at the time. They say this unknown major ocean extinction caused a more than 70 percent reduction in shark diversity and an almost complete loss of total abundance. Scientists said that the reason for this phenomenon remains a mystery.
Researchers say this single event has led to the virtual disappearance of sharks from open ocean sediments, a nearly 90 percent drop in abundance. He said the sudden extinction was independent of any known global climate event.
According to the research report published in the journal ScienceModern shark forms almost began to diversify within two to five million years after their extinction, but they represent a sliver of sharks only once.
a report in life science "Sharks have been around for 400 million years; they've suffered a lot of mass extinctions," said study co-author Elizabeth Siubert, a postdoctoral fellow at Yale University's Institute for Biospheric Studies and co-author of the study.
Siebert told Live Science that ichthyolites, the microscopic fossils of shark scales, are found in most types of sediment, but are small and relatively rare compared to other microfossils.
While scientists studied ichthyolites in the 1970s and '80s, only a few researchers examined them before Sibert, who conducted his doctoral investigations, which he completed in 2016. "As a scientist I've done a lot in my early career. Figuring out how to work with these fossils is what kind of questions we can ask about them," Sibert said.
For their new study, a co-author, Sibert and Leah Rubin, a graduate student at Atlantic College in Bar Harbor, Maine, at the time of the research, studied sediment cores extracted several years earlier by deep-sea drilling projects. From two different sites: one in the middle of the North Pacific, and the other in the middle of the South Pacific.
"We chose those sites specifically because they are far from land and they are far from any effect of ocean circulation or changing ocean currents," Sibert said.
Rubin, who is now a doctoral student at the State University of New York College of Environmental Science and Forestry, said the extreme nature of this decline in shark diversity was the most surprising aspect of the study to him as well. . The million-dollar question, says Rubin, is what causes it?
The paper is just the beginning, Siebert says, and hopefully it will be really interesting over the next decade to see what happened at the time that led to extinction among sharks.