June 4: It all started when palaeobiologist (someone who studies fossils of animals and plants) Elizabeth Sibert, based at Yale University’s Institute for Biospheric Sciences, along with her co- author Leah Rubin, decided to explore fish and shark populations over the last 85 million years. Several years ago, Sibert first tumbled upon hints of this mystery extinction.
The researchers examined two sediment cores that had been collected by drilling deep into the Pacific Ocean seafloor. The sediments contained fish teeth, shark denticles and other marine microfossils spanning forty million years.
Shark microfossils were found in the form of dermal denticles. Denticles are tiny scales about 0.1-0.5 mm in size and cover the shark’s body. A shark sheds thousands of denticles in their lifetime.
While examining the fossils, the researchers found one shark fossil for every five fish fossils in the sediments before nineteen million years. But they found only one shark fossil for every 100 fish fossils in samples newer than nineteen million years. The researchers concluded from the decline that a mystery event might have taken place nineteen million years ago which wiped out most of the shark population, the cause of which is unknown. It altered the ancient marine environment, and the sharks have since never recovered.
This finding helps us learn that sharks have been around for 400 million years, and have survived a lot of mass extinctions. Recent times also see a decline in shark population due to overfishing and other human activities. Sharks, being a major predator in the ocean, have to be saved to maintain the ecological balance.
By Shuchi Giridhar
