Was Megalodon Slimmer Than Previously Thought?

In the more than 400 million years that sharks have been swimming through Earth’s seas, none has been larger than Otodus megalodon. The great megatoothed shark reached more than 50 feet in length and prowled oceans the world over between 2.6 million and 23 million years ago. Despite the shark’s success and its fame as a massive apex predator worthy of multiple B-movies, paleontologists are still investigating what the giant shark actually looked like. And a new proposal suggests that O. megalodon was more slender than previously thought.

The latest study, published Sunday in Palaeontologia Electronica, draws from a portion of an O. megalodon backbone to suggest that the shark had a proportionally longer body than that of the modern great white shark. But some outside experts are doubtful about the new restoration.

Paleontologists have been investigating and revising the proportions of O. megalodon for decades. Experts principally work from teeth and vertebrae from the shark to estimate its size and proportions, which is common for prehistoric sharks, as their cartilaginous skeletons often decayed before fossilization. The shark’s spotty fossil record makes it challenging to get an exact idea of what the great fish looked like. “No complete skeleton of O. megalodon has been discovered yet, and that is why deciphering its body size and form have been so challenging,” says DePaul University paleontologist and study co-author Kenshu Shimada.

Just because a complete O. megalodon skeleton is unlikely to have been fossilized, however, doesn’t mean paleontologists are totally in the dark about what the shark looked like. O. megalodon belonged to a group of sharks called lamniformes, which includes species like the great white, salmon shark, porbeagle and others. The modern sharks share some key attributes with O. megalodon, such as body temperatures elevated above the surrounding seawater and preferences for fat-rich prey to help fuel their active lifestyles. O. megalodon probably resembled its modern relatives, but the details are still being discussed by experts.

The new study by Shimada and colleagues is the latest attempt to outline what O. megalodon might have looked like and is largely a response to a 2022 study from a different research team. Both studies are based on the same O. megalodon vertebrae, but they reached different conclusions.

In the latest study, the researchers scaled up a great white’s proportions so that its vertebrae would have the same diameter as the O. megalodon vertebrae. In this case, an O. megalodon with great white proportions would be about 30 feet long. However, the actual length of the partial backbone is about 36 feet—significantly longer than the great white model suggests. To resolve the discrepancy, the researchers propose that O. megalodon had a more elongated form than a great white of the same size would.

“Our new study suggests that we need to think outside the box when it comes to inferring the biology of O. megalodon,” Shimada says.

But the researchers behind the 2022 research are not convinced by the new hypothesis. “While alternative hypotheses should be and are welcomed in science, this particular proposal suffers from a circular logic,” says paleontologist Jack Cooper of Swansea University in Wales, who was not involved in the new study.

The new study says that the great white shark is an inappropriate analogue for O. megalodon, Cooper notes, but the new research also uses the great white shark for its comparisons of body form to the exclusion of other sharks. The 2022 study, by comparison, considered other lamniform sharks in addition to the great white and created a three-dimensional model. The 2022 study also produced an elongated O. megalodon model as one of its possible outcomes, as well, but researchers ruled it out based on data from a broader array of lamniform sharks.

Lacking a complete O. megalodon skeleton, such disagreements may seem difficult to resolve. “However,” Cooper says, “sharks have generally remained geometrically similar throughout their long evolutionary history, which means living sharks can be informative in reconstructing extinct ones.” Even when the shark’s record is mostly teeth and isolated vertebrae, scientists can still generate a rough idea of the megatooth’s shape based on physiology, what it likely fed on and other details gleaned from the fossil record.

Working out the shark’s form is critical to understanding how the megatoothed shark lived during its long tenure in Earth’s seas. “The body plan of megalodon is a key part of understanding its wider ecology, such as how fast it swam and what it needed to eat,” Cooper says. A longer shark would swim differently, for example, or have organs like the liver and spiral intestine related to the shark’s feeding and digestion. O. megalodon thrived for about 20 million years before vanishing, even as its preferred prey survived. Understanding the shark’s form can help experts uncover the carnivore’s evolution and extinction.

For the moment, however, Cooper and colleagues are not swayed by the new reconstruction. All researchers are agreed that O. megalodon was not simply a supersized great white, but what kind of shape the enormous shark took as it slid through ancient waters is only just beginning to come into focus.

Riley Black | | READ MORE

Riley Black is the author of The Last Days of the Dinosaurs and many other books. She is a science correspondent for Smithsonian magazine covering fossils and natural history, and she writes about the prehistoric past for a variety of publications.