Scans of a subset of its approximately hundreds of vertebrae — some the size of grapefruits — showed the shark had died at the age of 46. The researchers estimated the meg’s life expectancy to be around 88 to 100 years, implying that their specimen had been roughly “middle-aged,” Dr. Shimada said. They also back-calculated the shark’s size through its earliest years, and found it might have been more than six and a half feet long when it was born.
“That’s a really big baby,” said Mr. Cooper, who was not involved in the study.
To reach such a staggering size, burgeoning megs may have snacked on each other while still in the womb, Dr. Shimada said. Most sharks hatch from eggs inside their mothers’ bodies, then are birthed as live young. But the pups of some species don’t take kindly to roommates: Once hatched, they will begin to casually devour their unhatched siblings, which helps them beef up before being born.
“It’s this big, calorie-dense, nutritious meal that can help those embryos get bigger, faster,” said Allison Bronson, who studies the evolution of fish at Humboldt State University in Arcata, Calif., but wasn’t involved in the study.
With that much heft in tow, mini-megs might have emerged ready to duke it out with potential predators, or at least dwarf a good number of them in size. A voracious appetite, coupled with warm-bloodedness, might have helped them snarf down plenty of prey, allowing the juvenile terrors to bulk up even more.
Mr. Cooper said the study provided crucial data on a poorly understood animal. But he noted that some calculations it used were based on data gathered in the 1990s, when researchers relied more heavily on great white sharks to estimate aspects of megalodon anatomy. Drawing too close a comparison between the two animals, he said, can result “in underestimations in some specific body dimensions.”
It’s also hard to know how representative this one individual megalodon was of its species, Dr. Bronson said. “There’s a lot of variation in fishes,” she said. “Even fish of the same age, same species, can grow at really different rates and reach really different sizes.”
Researchers can’t know how difficult carrying and birthing a six-foot-plus pup might have been for megalo-moms. But “proportionally, while that baby is really big, so is the adult,” Mr. Cooper said. At maximum size, some megalodons might have spanned nearly the length of a bowling lane — plenty of space to house even a basketball-player-size embryo.