The ancient species of shark known as the megalodon (Carcharocles megalodon) was the biggest to have ever lived. Despite disappearing from Earth's oceans millions of years ago, this fearsome predator continues to fascinate us.
But how and why did the enormous predator, which could grow up to 66 feet long, go extinct?
When did the megalodon go extinct?
Megalodon first appear in the fossil record around 20 million years ago, having descended from a lineage that appeared about 60 million years ago. The species was found across Earth's oceans, except in the polar regions, and it would feed on whales, seals, turtles and other sharks.
But then, in less than one million years, it disappeared.
"Right now we have the extinction date pinned down to an 800,000 year period, between 4 and 3.2 million years ago, with the highest likelihood of going extinct about 3.5 million years ago," Robert Boessenecker, of the College of Charleston's Geology and Environmental Geosciences Department, told Newsweek.
He said paleontologists have "no idea" how fast the extinction took place, but that even the timeframe mentioned above could be considered rapid in geological terms.
What happened to the planet's biggest sharks?
There is debate among the scientific community about what factors caused the megalodon to go extinct.
For some scientists such as Boessenecker, the answer could be relatively simple. He and his colleagues have hypothesized that megalodon went extinct as a result of great white sharks.
"We think that C. megalodon was outcompeted by the modern great white shark (Carcharodon carcharias,) which evolved serrated teeth around 5 to 6 million years ago, and became a worldwide-distributed species around 4 million years ago," he said.
"After leaving the Pacific, it overlapped nearly completely with C. megalodon, and likely competed for prey. This is based on the timing and our dating of the extinction to about 3.6 million years ago," he said.
However, as Boessenecker concedes, this is still a hypothesis and academic consensus on the question is lacking.
Paleobiology PhD Student Jack Cooper, of Swansea University, U.K., told Newsweek that other factors—such as the reduction of coastal habitats amid dramatic sea level changes—could also have played a role: "Unfortunately, there isn't a single direct answer like with the dinosaurs, where we know it was primarily down to a big asteroid," he said.
"During the Pliocene, between 5.3 and 2.6 million years ago, sea levels were changing constantly and quite dramatically. This will have naturally reduced coastal habitats, which we know megalodon lived in to find food and use nursery areas for its young.
"With these habitats reduced, there was less area for megalodon to live in and less food available. Given the megalodons enormous size, and its main prey likely being whales, less food would have meant megalodon likely couldn't have met its energetic demands," he said, adding that competition from great white sharks could also have been a factor.
What the meg can teach us about sharks and oceans today
One thing that megalodon experts do seem to agree on are the insights their work on the ancient apex predators can give us into modern sharks—and their place in Earth's changing oceans.
This includes the possible destiny of modern sharks, many of which could, like their enormous ancient ancestors, eventually vanish from the oceans. This would have a profound impact on ocean ecosystems.
"Megalodon is a fantastic case study for future extinctions because it was an apex predator that lived all over the world transporting nutrients and regulating prey populations," Cooper said. "Its extinction tells us that large sharks are sensitive to food availability and sea level changes in coastal areas. But it also tells us that if and when these sharks disappear, the food web will be put out of balance by trophic cascades as their prey species increase in abundance and overeat their own prey as a result.
"Essentially, the food web and how it operates changed when this one very big worldwide shark went extinct, so the effects will be much more dramatic if more sharks disappear."
Boessenecker said megalodon research was invaluable to our modern day understanding of just how important big sharks are in our ocean's ecosystems.
"I fully expect that, if our hypothesis is correct—that modern great whites outcompeted C. megalodon—that modern great whites probably drive the ecology and survivability of other predatory sharks," he said.
"Many modern shark species are threatened or endangered, and the fact that the introduction of one new species may have been all that was needed to topple an apex predator lineage that had ruled the oceans for around 30 million years tells us that marine ecosystems—even without human-mediated climate change, ocean acidification, pollution, and microplastic accumulation—are likely more fragile, and poorly understood, than most people acknowledge."
