Sharks Almost Went the Way of the Dinosaurs 19 Million Years Ago
Anti-aristarchus writes:
Recent story at The New York Times:
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.
This abundance makes them valuable to scientists seeking to understand the past, said Paul Harnik, a paleobiologist at Colgate University, not involved in the research. "It's a sheer numbers game."
[...] About halfway through her data set, Dr. Sibert spotted an abrupt change in the fossil record. Nineteen million years ago, the ratio of shark denticles to fish teeth changed drastically: Samples older than that tended to contain roughly one denticle for every five fish teeth (a ratio of about 20 percent), but more recent samples had ratios closer to 1 percent. That meant that sharks suddenly became much less common, relative to fish, during an era known as the early Miocene, Dr. Sibert concluded.
No doubt it was the lasers on their heads.
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