While examining fossil records from the depths of the ocean scientists discovered sharks were nearly wiped out in a mysterious and "major extinction event".
Small shark and fish fossils showed shark numbers were abundant for 40 million years, with populations estimated to be 10 times higher than today.
Then about 19 million years ago the remains started to vanish.
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It's not known what lead to the die-off, which is said to have occurred at a relatively stable time.
"There is no known climatic and/or environmental driver of this extinction, and its cause remains a mystery," researchers wrote in their findings, published today in Science.
"Modern shark forms began to diversify within two to three million years after the extinction, but they represent only a minor sliver of what sharks once were."
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The extinction event saw shark diversity plummet by 70 per cent.
Modern shark populations have not recovered.
Today there are just over 1,000 species of sharks and rays.
Over-fishing, pollution and climate change remain the predators' big threats.
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