The fossil record indicates this species dominated oceans during that period, before eventually dying out.
But without a complete fossilised skeleton ever having been found – because cartilaginous fishes’ soft skeletons are unlikely to be preserved – paleontologists have to rely on studying teeth, the toughest part of any shark’s body.
A new study, examining measurements taken from the same group of sharks as the Otodus megalodon, indicates the maximum body size it could have reached would have been huge: about 15m (50ft) in length – or “off the charts in the shark world”, according to the research team.
In comparison, large great white sharks can grow to more than 6m (20ft) long. Meanwhile the blue whale, a mammal, is still far larger, reaching 30m.
The only other sharks which have been able to approach the scale of the megalodon are a few plankton-eating species such as the whale shark and basking shark.
The new research illuminates exactly how uniquely gigantic the shark was, according to Kenshu Shimada, a paleobiologist at DePaul University in Chicago and lead author of the study.
“Lamniform sharks have represented major carnivores in oceans since the age of dinosaurs, so it is reasonable to assert that they must have played an important role in shaping the marine ecosystems we know today,” said Dr Shimada.
Warm-bloodedness has previously been proposed to have led to the gigantism (over 6m, or 20ft) in multiple lamniform lineages.
But the new study proposes a reproductive strategy with a unique cannibalistic egg-eating behaviour among early hatched embryos, which takes place while still inside the mother.
The scientists said this could nourish early-hatched embryos and be another possible cause for the frequent evolution of gigantism achieved by lamniform sharks.
“This is compelling evidence for the truly exceptional size of megalodon,” said co-author Michael Griffiths, a professor of environmental science at William Paterson University in Wayne, New Jersey.
Co-author Martin Becker, also a professor of environmental science at William Paterson University, added, “this work represents a critical advancement in our understanding of the evolution of this ocean giant.”
The study is published in the journal Historical Biology.