Millions of years ago, sharks were on the brink of extinction, a new study reveals. Scientists, however, do not know what could have caused the massive death of the sharks.
By analyzing fossils collected from sediments in the Pacific Ocean, researchers discovered that, 19 million years ago, the shark population on the planet fell sharply. The reason behind this newly discovered mass extinction is still unknown.
“It’s a great mystery. Sharks have been around for 400 million years. They’ve been through hell and back. And yet this event wiped out [up to] 90 percent of them,” says Elizabeth Sibert, paleobiologist and oceanographer at the Yale University and author of the study.
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The discovery came almost accidentally. Sibert is studying microfossils of fish teeth and shark scales in deep-sea sediments and simply decided to record the abundance of fish and sharks over 85 million years.
“just to get a sense of what the normal variability of that population looked like in the long term. What we found, though, was this sudden drop-off in shark abundance around 19 million years ago, and we knew we had to investigate further,” the scientist shared.
According to Sibert, the number of shark deaths was at least twice the number of sharks that died during the Cretaceous-Paleogene mass extinction event 66 million years ago. The collision of an asteroid with Earth on that occasion wiped out 75% of the plant and animal species on our planet.
According to the researchers, it is unknown that any climatic calamity or alteration of the terrestrial ecosystem occurred during the period when sharks almost disappeared from the face of the Earth.
“This interval is not known for any major change in Earth’s history, yet it completely transformed the nature of what it means to be a predator living in the open ocean,” Sibert stressed.
After the mass extinction, which likely occurred in an interval of fewer than 100,000 years, the diversity of sharks in Earth’s oceans was never the same again. Many open ocean species disappeared completely. The coastal sharks had a bit more luck, the researchers say. The lineages that exist today are derived primarily from these survivors.
The scientists further discovered that, in the sediment samples deposited after the extinction event, there were no new types of shark denticles. This suggests that few new species of these sharks have emerged since.
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“That’s a worrisome discovery, as it could mean sharks have a hard time recovering from abrupt extinction events – and unfortunately, we are now entering another,” ScienceAlert stressed.
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