Study Reported a Massive Shark Die-Off 19 Million Years Ago
A 2021 study reported that open-ocean sharks may have lost over 90% of their abundance about 19 million years ago, but the cause and scale remain debated.
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About 19 million years ago, researchers found an unusual change in the fossil record of open-ocean sharks. A 2021 study examined tiny shark skin scales, called dermal denticles, preserved in deep-sea sediments from the Pacific. The researchers reported a sharp decline of more than 90% in shark abundance and more than 70% in denticle diversity around the early Miocene, suggesting a major extinction event in pelagic sharks. The proposed event did not line up with a known major global climate shift, so its cause remained unknown. Later scientists challenged the interpretation, arguing that changes in sedimentation rates, sampling, denticle variation within individual sharks, and shifting species ranges could produce some of the observed pattern. The original researchers responded that their methods accounted for changes in sedimentation and continued to defend the evidence for a major extinction. The result is an intriguing scientific dispute rather than a settled explanation of exactly what happened to sharks 19 million years ago. This ancient event is also distinct from the modern decline of oceanic sharks, which has been strongly linked to fishing pressure. Modern studies have documented substantial declines in oceanic shark and ray abundance since 1970, making the ancient fossil mystery especially interesting while keeping the two events scientifically separate.
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