Five million years ago, huge predatory sharks patrolled the oceans. Its giant teeth — left behind in coastal sediments — inspired the 1843 name that has since become a household word: megalodon.
Despite the megatooth shark’s fame, however, the exact size and shape of the megalodon has been a matter of debate. Because shark skeletons are largely made of cartilage, they rarely fossilize, leading researchers to make wildly varied estimates — from 10 to 18 meters — using fallen teeth and comparisons with living relatives like mackerel sharks and the great shark. White shark.
But new 3D modeling of the shark, published Wednesday in the journal Science Advances, suggests that the megalodon may have been a larger, faster and more widespread animal than previously thought.
In 2014, Catalina Pimiento, a paleontologist at Swansea University in Wales (UK), met John Hutchinson, an anatomist at the Royal Veterinary College in London. Hutchinson specializes in computer modeling of extinct animals. The two eventually joined a team of collaborators to build a 3D computer model of a megalodon, based in part on scans of a preserved spine discovered in the 1860s and held at Belgium’s Royal Institute of Natural Sciences. They also used megalodon teeth and a full-body scan of a great white shark, the closest living analogue of megalodon.
The resulting model suggested a 15-meter-long, 67-ton animal, almost as big as a whale shark. It’s possible that other megalodons were even larger, Pimiento said; there are other fossilized vertebrae that are 50% larger than those used in the model, suggesting a maximum length of 20 meters, longer than a modern humpback whale. The megalodon model’s jaws could open wide enough to devour an 8-meter orca in just five bites.
How reliable is this computational modeling?
“These reconstructions work very well when applied to living animals whose mass we know, so they seem to be right in general,” Hutchinson said. This is especially true given the natural variations in size between individual animals.
But some researchers point out that the model is based on assumptions about megalodons that have not been confirmed in the fossil record.
“The size and shape of other skeletal components such as the skull, jaws and all fins remain speculative,” said Kenshu Shimada, a professor of paleobiology at DePaul University in Chicago.
If the team’s model is accurate, however, it has implications for the cruising speed of the huge predators — how quickly an animal gets from point A to point B — and their appetite. The team found that the megalodons could reach a cruising speed of approximately 5 km/h, Pimiento said, much faster than the other 33 sharks surveyed. Among existing sharks, the highest cruising speed is that of the salmon shark, which can reach about 3.2 km/h.
Because the slower-moving great white shark can travel nearly 11,000 kilometers without stopping to prey on seasonal prey, the team argued, the megalodon could probably go much further. In fact, he would have to to keep himself fed. While fossil remains from Peru have shown that the megalodon occasionally hunted seals, the shark’s “large body size and potential energy demands suggest it would need high-calorie prey such as whales,” Pimiento said.
In modern ecosystems, Hutchinson pointed out, large migratory animals play an important role in the flow of nutrients — deposited in dung or carcasses — around the world. As a transoceanic superpredator, the megalodon likely played a similar role in ocean ecosystems tens of millions of years ago, when sea levels were barely higher than they are today.
But cutting-edge predators are often vulnerable to a changing world. In the Pliocene era, increasing ice at the poles led to frequent sea level changes and the loss of important offshore habitats. An accompanying extinction event led to a decline in large prey, likely forcing the megalodon to compete directly with smaller sharks such as the great white. The last of the huge predators disappeared 3 million years ago.
“It would be safe to assume that their extinction had global-scale impacts on food webs from the top down,” Pimiento said.
The team’s model therefore suggests that the megalodon was not just physically larger than previously assumed; it probably also played a bigger role in ocean systems, making them poorer — though safer — in their wake.
