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When the sharks were about to go extinct

19 million years ago, sharks nearly disappeared from Earth’s oceans, according to a new study that offers evidence for a previously unknown oceanic mass extinction event.

As a species, the sharks never recovered from that event, according to study authors Elizabeth Sibert of Harvard University and Leah Rubin of the College of the Atlantic, both entities in the United States.

The data obtained in the new study suggests that today’s diversity of sharks is only a fraction of what it once was.

Much of what is known about ancient ocean ecosystems is derived from rock and fossil records, which are generally limited to shallow water deposits and provide only a small glimpse into the history of marine species throughout the ocean.

On this occasion, using a different data set (small fossils in global deep-sea sediment cores), Elizabeth Sibert and Leah Rubin provide new insight into the changes in abundance and diversity of one of the ocean’s largest predators.

Using microfossils in the sediment cores called ichthyolites, scales, and detached teeth from sharks and other bony fish that accumulate naturally on the seafloor, Sibert and Rubin constructed a record of shark diversity and abundance that spans nearly the last few. 40 million years.

A modern shark. (Photo: Dwayne Meadows / NOAA / NMFS / OPR)

According to the findings, sharks practically disappeared from the record during the early Miocene, approximately 19 million years ago, reducing their abundance by more than 90% and their morphological diversity by more than 70%. This puzzling extinction event appears to have occurred independently of any known global climate event or terrestrial mass extinction.

While the causative factors remain unknown, the authors suggest that this event fundamentally altered the ecology of pelagic predators and subsequently laid the foundation for the great lineages of migratory sharks that now dominate Earth’s oceans.

The study is titled “An early Miocene extinction in pelagic sharks.” And it has been published in the academic journal Science. (Source: AAAS)

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