Sharks have existed for most of half a billion years. They were around before there were trees; they survived numerous mass extinctions that wiped out most of life from Earth. By any measure, they are one of the most successful species on the planet.
Yet a surprising new discovery has revealed that they have come dangerously close to extinction forever – and have not yet recovered from the blow.
“In fact, we discovered this event entirely by accident!” Study leader Elizabeth Sibert told IFLS in an email. “[W]We didn’t expect to find any change in the shark community, much less a huge extinction! “
Siebert, along with co-author Leah Rubin, made the discovery while studying microfossil fish teeth and shark scales. Very little is known about this rather niche of micropaleontology, Sibert explained, and the original goal of the project was simply to gain a better understanding of the natural biodiversity of the ocean.
“We decided to generate a long record of an abundance of fossil fish and sharks, going back many millions of years in the same place, just to see what the normal variability of the background is,”
The study reveals that for tens of millions of years, the ratio of fish to shark fossils has been largely constant, around one shark fossil for every five fish fossils. But then, 19 million years ago, trouble happened. This ratio has suddenly dropped to less than one shark fossil for every hundred fish, reflecting a shark decline of more than 90 percent.
Almost everything about this discovery is a surprise. The time period in which it occurred was “unnoticeable earlier,” commented paleobiologists Catalina Pimento and Nicholas D. Penson, who did not participate in the original study. Moreover, they note, the reasons for this “extinction of large sharks in … the largest ecosystem on Earth” is something that researchers have yet to discover.
“The climate and / or environmental driver of this extinction is unknown, and the cause remains a mystery,” said a report by Siebert and Rubin published last week in Science. “Modern forms of sharks … represent only a small fraction of the sharks they once were. “
In fact, Siebert explained, we don’t even have a clear idea of the scale of the crash. The results showed that the sharks were heavily affected by the event, but whether other parts of the ocean ecosystem were affected and if so, how remains unknown.
And the fact that the number and diversity of shark populations have not yet recovered from the event is just another mystery that scientists have to deal with.
“We’re not sure why shark populations and diversity have never recovered since the event,” Siebert told IFLS. “One hypothesis is that during the effects of extinction, sharks were less adapted to new ecological or ecological conditions than other large marine predators, such as whales – so that under the new conditions, other organisms were able to diversify and evolve, effectively outpacing surviving sharks. “
“Like most research endeavors, this first report offers more questions than it can answer,” Rubin added.
But unexpected findings are important not only for our understanding of the past – they also contain a clear message for the future. Marine predators such as sharks and whales are dying at alarming rates, and this discovery could potentially give an idea of the impact it will have on other ocean life.
“The current state of declining shark populations is certainly a cause for concern,” Rubin said. “This [paper] is a vital first step in understanding the consequences of a dramatic decline in these most marine predators of modern times. “
What these consequences will be is something we may find out about ourselves depressingly soon – but this new discovery may shed some light on what to expect, the authors explain.
“[S]harks … play such a large and important role in marine ecosystems and when their numbers are destroyed, it can turn the ecosystem into a whole new state, even if it has been stable for tens of millions of years, “Siebert warned.” We humans are now fast we are reducing the populations of most large vertebrate predators in today’s oceans – I’m afraid we’re racing to a tipping point, perhaps like the one we saw 19 million years ago. “
But for Sibert and Rubin, the future is exciting.
“…[T]there’s so much more to learn about the earth, “said Sibert.” Sharks have been around for more than 400 million years, and yet this event, which we didn’t even know about, nearly removed them from the oceans just 19 million years ago. We didn’t know because we didn’t we were looking. “
“There will always be more to find,” she added. “What next?”
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