Shimada’s team determined that megalodons must have been at least 14 meters long, twice as long as any other shark that isn’t a filter feeder, using their fossilized teeth. Other now-extinct species that exhibited traits of gigantism like the megalodon weren’t nearly as long though, only growing to be about six meters in length. It was that discrepancy between megalodons and similar species that led Shimada’s team to believe there must be more to the story, and that’s how the team arrived at cannibalism.
Sharks reproduce through ovoviviparity, which is a reproductive method where embryos develop inside eggs and stay inside their mother’s womb until they hatch. This method of reproduction is inherently cannibalistic in this species because the first baby shark, or pup, to hatch then eats the rest of the eggs in the womb in a behavior known as intrauterine cannibalism. That’s why when the pup finally leaves its mother’s womb, it’s already grown to be quite large and capable of defending itself.
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Shimada’s team believes that the intrauterine cannibalism combined with the environmental conditions the species experienced, like favorable water temperatures and the availability of food, led some shark species like the megalodon to grow into such a gigantic size. Calvert Marine Museum paleontologist, Stephen Godfrey, says that still doesn’t explain the greater gigantism the megalodon experienced versus other gigantic shark species though.
University of Bristol paleontologist, Humberto Férron, told Science News that he believes the megalodon’s unique gigantism must have been the result of its ovoviparity reproductive strategy coupled with intrauterine cannibalism, as well as the species’ endothermy and access to large prey for food.
While the megalodon species is extinct, nothing’s stopping you from watching Jason Statham battle a megalodon in The Meg. You can read about why we think that movie was good in our review of The Meg. If you’re looking for some more underwater science to read about, check out this story about how scientists resurrected 100 million year-old underwater lifeforms and then read this story about a bionic moon jellyfish created by scientists.
Wesley LeBlanc is a freelance news writer and guide maker for IGN. You can follow him on Twitter @LeBlancWes.