For millions of years, C. megalodon, one of the largest predators to ever live on Earth, trolled nearly all the planet's oceans. Researchers have found evidence of the giant sharks stretching back 20 million years, but the species vanished from the fossil record about 2 million years ago.
The sharks went extinct at a time when glaciers covered large swaths of the globe, "and some people think that may be related to the extinction of this species, but it hasn't been established," said Catalina Pimiento, a Megalodon researcher with the University of Florida and the Smithsonian Tropical Research Institute.
Like sharks alive today, the prehistoric Megalodon's skeleton was made of cartilage, not bone, so the creatures left little behind for researchers to study. "The only remains you can find in the fossil record are the teeth, because they're hard enough to preserve through geologic time," Pimiento said.
Although that may not seem like much to go on, scientists have been able to use equations based on their knowledge of great white shark physiology — the modern-day species that most closely resembles Megalodon — to extrapolate just how big the ancient sharks grew.