It’s not hard to see why Megalodon, an epic species of shark that died out some 3.6 million years ago, has captivated the public imagination and become the star of movies like The Meg. Because Megalodon has become such an iconic sea monster, most people picture the species as its pop culture incarnation: A beefed-up great white shark with a thirst for human blood. But here’s the thing: Nobody actually knows what the giant sea creature, which is officially named Otodus megalodon, looked like.
According to a study published on Sunday in Historical Biology, “all previously proposed body forms for O. megalodon should be regarded as speculations because there are no scientific means to decisively support or refute the accuracy of any of them.”
“Although some pop culture representations of Megalodon are overly exaggerated in size, most of them do actually depict it to be somewhat like the modern great white shark and its close relatives,” said Kenshu Shimada, a paleobiology professor at DePaul University in Chicago who co-authored the new study, in an email.
“I would not be surprised if Megalodon indeed looked like such modern species that have been used as analogs, but the new study suggests that it cannot be scientifically substantiated based on the present fossil record,” he added.
Based on the fossils left behind by this predator, we know that this shark was the biggest fish to ever roam the sea, measuring at least 50 feet in length. However, Megalodon’s immense size and evolutionary success over millions of years does not translate to a robust fossil record. This extinct hunter is primarily known from its sharp flesh-tearing teeth and a few vertebrae, which are about the only parts of the animal that are conducive to fossilization.
“As a member of cartilaginous fishes like all other sharks, the skeleton of Megalodon was poorly mineralized and thus had poor fossilization potential,” Shimada said. “Its vertebrae were weakly calcified and thus are occasionally preserved, but much of the fossil record of the prehistoric species is known from its hard well-mineralized teeth.”
In the absence of fossils, many scientists have tried to use models, reconstructions, and modern comparisons in an attempt to make educated guesses about its appearance. For instance, a 2020 study published in Nature inferred Megalodon’s body dimensions by examining five species of modern warm-blooded sharks in the family Lamnidae that are presumed to be ecologically and physiologically similar: Great white sharks, shortfin mako sharks, longfin mako sharks, salmon sharks, and porbeagles. Based on that approach, the study found that the average Megalodon likely sported a 5-foot dorsal fin and 13-foot tail, with a head that measured 15 feet in length.
In the new study, Shimada and his colleagues—including lead author Phillip Sternes, a biologist at the University of California at Riverside, and DePaul graduate student Jake Wood—outlined the pitfalls of these comparative approaches. The team analyzed 15 living species in the Lamnidae family, including some that are cold-blooded, such as the basking shark.
The results suggested that there is no clear relationship between the body form of these sharks and their classification as warm-blooded or cold-blooded. Shimada and his colleagues ultimately conclude that Megalodon’s body form cannot be reconstructed on the assumption that it is similar to warm-blooded living sharks, as it could have taken on a variety of other forms. The only way we will ever get a sense of this amazing predator’s true appearance is if scientists are able to discover a more complete specimen, the team said.
“I wish there were other means to better infer the body form of Megalodon, but what we really need are indeed actual fossil remains other than teeth and vertebrae,” noted Shimada. “Even if one can discover a small section of the skeleton, such as a skull or fin, it would offer more clues about the shark's original body form.”
Hopefully, we will luck out with such a major find soon. Until then, the world’s biggest fish will remain a shadowy figure for scientists, even as it stars as the ultimate super-sized shark on the big screen.