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In movies and TV shows, the ancient megalodon, or megatooth shark, has taken on a near-mythic status. The extinct creature lived 15 million years ago and was likely the largest carnivore ever to exist. This apex predator is thought to have been capable of taking down large whales and munching through 2,500 pounds of prey per day.
But we may have misunderstood the gigantic sea creature’s actual size and shape. Over the years, scientists have described the megalodon as having a stocky, bulbous build, similar to that of a modern-day great white shark and have estimated that it measured a maximum of 66 feet in length.
Now, new research from a team of 28 global shark, fossil, and vertebrate anatomy experts shows the creature probably had a slender elongated body instead—and could have grown to nearly 80 feet, the length of a blue whale. The findings, published in the journal Palaeontologia Electronica, not only help us understand the megalodon but offer some insight into gigantism, the evolution of especially large body sizes, in the ocean.
While the megalodon was around for millions of years, it left only a few clues behind about its physical anatomy. Scientists have found plenty of its giant serrated teeth—each shark had 276 of these tiny daggers in their mouths, which measured up to at least 6 inches in length. Otherwise, the ocean graveyard has served up only fragments of cartilage, a few dermal denticles—the shark’s outer skin scales—a smattering of vertebrae, and one 36-foot fossil vertebral column from Belgium. No complete skeletons have ever been found.
Its pups could have measured about 13 feet long, as large as an adult great white.
From studies of the megalodon’s large serrated teeth, scientists made inferences about the shark’s diet and ecology and assumed similarities in shape between the ancient shark and the modern-day white shark. “You can assume, since they have similar ecology, they would have the same body shape pattern,” says Phillip Sternes, a shark biologist and educator at SeaWorld who co-authored the new research. “But there’s no fossil evidence to support this.”
To build their new anatomical model, the authors surveyed the proportions of 145 modern and 20 extinct species of sharks—looking at the lengths of their heads, bodies, and tail sections relative to total body length. When they compared the proportions of the megalodon fossil fragments to the bones of living sharks, they found they didn’t match those of the white shark at all—instead, they were more like those of a lemon or porbeagle shark, with a slender, torpedo-like frame that could glide through the water. They also noticed while completing their survey that modern-day gigantic sharks, such as the whale shark and basking shark, and other gigantic aquatic vertebrates, such as whales, have the same slender body shape.
“It makes total sense,” says Sternes. “After you get to a certain size, you start to become much more elongated for the energetics and swimming.” It helps to reduce drag. The white shark, which reaches about 18 feet in length, uses its stocky body to muscle its way up from depths to grab prey at the surface. But if it were to grow any larger, such proportions would make it difficult to hunt and swim. Kenshu Shimada, a biologist at DePaul University and the study’s first author, says it remains a mystery why some vertebrates grow to gigantic sizes while others do not.
Sora Kim, a paleoecologist at the University of California, Merced who researches megalodons, says she appreciates that the authors started out with an open mind about the body shape of the fossil shark. “The starting assumption for many megalodon studies is to associate them with white sharks,” says Kim, who was not involved in the new research. “This study proposes some alternate starting points for comparisons.”
After you get to a certain size, you start to become much more elongated for the energetics and swimming.
Kim says that whenever she gives a presentation on the ancient shark, either to the public or scientists, the two questions she gets are “what did they eat?” and “why did they go extinct?” She’d love to get to the bottom of those queries. “We have a better understanding of megalodon ecology from recent research, but we still don’t have definitive answers to these questions.”
Sternes says the study findings, which include new analyses of the Belgian vertebral column, which is marked by growth rings, hint at the daily life of the shark. That specimen would have weighed around 94 tons and traveled at a speed of 1-2 miles per hour. Its pups could have measured about 13 feet long, as large as an adult great white and about double previous estimates for megalodon pups. Such a size would represent the largest of any pup in all the evolutionary history of fishes. These pups probably lived in coastal waters and were hunting for their breakfast of marine mammals almost from birth, the researchers surmise.
Megalodon sharks could have lived to 500 years of age, and may have continued growing their entire lives, Sternes says—although this is still a hotly debated subject. Greenland sharks can live to be 400 years old, but they grow slowly and live in cold, deep waters—unlike the megalodon, which had a fast metabolism and lived in warmer coastal environments.
How did it get so big? The shark ate, constantly, throughout its life, Sternes says. “It’s basically just a big swimming, eating machine that’s going to be eating everything.” Instead of using bursts of speed like the great white, it probably just pursued marine mammals in a long chase sequence, and eventually took them down by the tail.
What eventually happened to the megalodon is also still a mystery. The giant disappears from the fossil record around 3.5 million years ago—around the same time the great white shows up on the planet. Sternes guesses it was a combination of factors: A changing climate meant cooler water temperatures which forced the sharks to work harder to stay warm, prey became less abundant, and competition increased from newer species like the great whites. The overlapping pressures eventually caused the demise of the megalodon. Just look at the dinosaurs, he says: “Bigger is not always better.” 
Lead image: Martin Spurny / Shutterstock
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