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Sharks nearly went extinct 19 million years ago — and scientists have no idea why

About ninety percent of sharks seem to have mysteriously disappeared 19 million years ago (Credits: Brad Leue/Barcroft Media via Getty Images)

Almost every shark in the world mysteriously vanished 19 million years ago in an extinction event that has baffled researchers.

Some 90% of sharks are thought to have disappeared in the event, with those that remaining far less diverse in size, shape and structure. But scientists have no idea why.

What is known is that sharks never recovered from the die-off, which researchers say was even more catastrophic, albeit far slower, than current human-driven decline.

US scientists Elizabeth Sibert and Leah Rubin discovered the extinction event while studying two ancient sediment core samples collected from the North and South Pacific in the 1980s and 1990s.

They searched the samples, taken from deep in the seabed, for old shark teeth and scales which naturally drop to the ocean floor.

These fallen scales and teeth are slowly buried under new layers of sediment, creating snapshots of the creatures that lived in the ocean millions of years ago. By comparing different layers, scientists can get an idea of changes in biodiversity.

Rubin told tech publication Ars Technica: ‘Dermal denticles offer an incredible window into the past of these ancient and elusive marine predators and thus the state of ocean ecosystems through time.’

According to the samples, sharks were abundant up to around 19 million years ago, when the number and type of teeth and scales plummeted.

With no known climate events at the time to explain the decline, scientists are at a loss to understand it.

But they think the mystery will be solved with more research and sediment samples.

Sibert told Ars: ‘One of the challenges with this particular bit of research is ‘what happened to the sharks at this time and why was there this massive die-off?’ The answer is ‘we really don’t know right now.”

What is certain is that shark species are experiencing a much faster decline today from human actions like overfishing, according to marine researchers Catalina Pimiento and Nicholas Pyenson.

They wrote in the journal Science, which published Sibert and Rubin’s study: ‘Despite recent improvements in conservation actions, few countries impose restrictions that target oceanic sharks.

‘[Ancient] shark communities never recovered from a mysterious extinction event 19 million years ago; the ecological fate of what remains is now in our hands.”

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