Meet the Megalodon

The megalodon was the largest fish to ever swim in Earth’s oceans. Longer than a school bus and with a fin taller than a seventh-grader, the fearsome beast went extinct 3.6 million years ago. So biologists like Kenshu Shimada at DePaul University in Chicago, Illinois, have to do some serious science to study these prehistoric animals.

The megalodon belongs to a group called Lamniformes, which includes species like mako, goblin, basking, and great white sharks. It was the only supersized shark that didn’t eat plankton, which are small microscopic organisms that live in the ocean. Many of the largest sharks feed on plankton, including whale sharks—the largest alive today.

The megalodon was the largest fish to ever swim in Earth’s oceans. It was longer than a school bus, and its fin was taller than a seventh-grader! But the fearsome beast went extinct 3.6 million years ago. So biologists like Kenshu Shimada at DePaul University in Chicago, Illinois, have to get crafty to study it.

The megalodon is related to living species like mako, goblin, basking, and great white sharks. But it was far bigger than those animals—and even bigger than whale sharks, the largest fish alive today. Many of the largest living sharks eat plankton, microscopic organisms that live in the ocean. But the megalodon didn’t. It hunted much bigger prey.

Most of the megalodon fossils found so far are teeth. That’s because sharks have squishy skeletons made of cartilage, which is the strong connective tissue found in your nose and ears. Cartilage does not usually fossilize. So Shimada has to get creative. “I enjoy the challenge of finding ways to infer the biology of prehistoric sharks by studying the anatomy of present-day sharks,” he says.

To estimate the megalodon’s size, Shimada measured the teeth of 13 species of present-day sharks  in the Lamniformes group that don’t eat plankton. He used that data to estimate body lengths of extinct sharks in the group. Compared with the other extinct sharks, the megalodon stood out as an exceptionally gigantic shark.

Sharks have squishy skeletons made of cartilage. This strong, flexible tissue is also found in your nose and ears. Cartilage does not usually fossilize. That means most of the megalodon fossils that scientists find are teeth. To learn about the prehistoric shark’s body, Shimada makes inferences based on the bodies of present-day sharks. “I enjoy the challenge,” he says.

To estimate the megalodon’s size, Shimada measured the teeth of 13 of its living relatives that don’t eat plankton. He knew the body lengths of the living species. He used that data to estimate the body lengths of extinct sharks in the group. Compared with the other extinct sharks, the megalodon stood out. It was exceptionally gigantic!

Shimada’s newest study shows that, even at birth, a megalodon was a big fish—more than 6 feet long! This not only indicates that megalodon gave birth to babies instead of laying eggs, but it also suggests that megalodon embryos grew so large inside their mother by eating unhatched eggs while still in the womb. “The behavior, known as oophagy, can be viewed as a form of cannibalism,” Shimada explains. Although it sounds gross, oophagy is a very common behavior in these types of sharks—and is the best explanation for how megalodons grew so big!

Shimada’s newest study shows that even baby megalodons were enormous. At birth, the big fish were more than 6 feet long! That means megalodons gave birth instead of laying eggs, according to Shimada. It also suggests that after hatching inside their mother, megalodon embryos grew by eating unhatched eggs in the womb. “The behavior… can be viewed as a form of cannibalism,” explains Shimada. It sounds gross, but it’s a common behavior in this type of shark. And it’s the best explanation for how megalodons grew so big!