Sharks Almost Went the Way of the Dinosaurs 19 Million Years Ago

Analysis of the fossil record shows a mysterious mass extinction that decimated the diversity of sharks in the world’s oceans, and they’ve never fully recovered.

Extinctions that obliterate wide swathes of life have reshaped Earth’s history. Typically triggered by a massive environmental change — like an asteroid impact or a significant shift in climate — these events give scientists an intimate look at how life recovers after a cataclysm. Researchers believe they’ve now pinpointed a previously unknown planetary-scale reset that occurred about 19 million years ago. This extinction event transpired in the world’s oceans, and decimated shark populations. The boneless fishes still have not recovered from the damage, the team suggests in a paper published Thursday in Science. Scales cover the bodies — and even the eyeballs — of sharks. Known as “dermal denticles,” these scales function like protective armor and their ridges also reduce drag as the animals swim, said Elizabeth C. Sibert, an oceanographer and paleontologist at Yale University. These scales are microscopic — each one is only about the width of a human hair — but sharks slough off about 100 denticles for each tooth they lose, making them common in the fossil record.