Why did the mega-shark megalodon die out? It could have been its highly active metabolism, new research suggests.

The great white shark (Carcharodon carcharias) may have wiped out the giant megalodon (Otodus megalodon).

Millions of years before human beings emerged, a type of shark that grew up to 60 feet (18 meters) long prowled the oceans. Based on the fossil record, scientists suspect that O. megalodon died off about 2.6 million years ago, around the time a lot of other marine species went extinct. (Researchers even recently suggested that the mass die-off may have been the result of a nearby supernova.) [These Bizarre Sea Monsters Once Ruled the Ocean]

But scientists may have miscalculated megalodon's time of death by about 1 million years.

For a paper published today (Feb. 13) in the journal PeerJ, researchers re-examined the fossil record of megalodons in California and Baja California, Mexico, where many examples of the huge fish have been found.

There's clear evidence that up until about 3.6 million years ago, megalodons were alive in the ocean. But after that, things get dodgy. Fossils dated to between 2.6 million and 3.6 million years ago tended to have issues. Many of the fossils seemed to have shifted within the surrounding rock in ways that complicate the dating methods scientists use.

But if megalodons died out 3.6 million years ago, they weren't part of that mass marine extinction. So, what killed them?

The researchers in the new study suggested that the huge sharks were outcompeted by a smaller, savvier predator.

Great whites arrived in the oceans about 4 million years ago, just 400,000 years before megalodon's revised death date.

"We propose that this short overlap (3.6 to 4 million years ago) was sufficient time for great white sharks to spread worldwide and outcompete O. megalodon throughout its range, driving it to extinction," College of Charleston paleontologist Robert Boessenecker, an author of the study, said in a statement.

Boessenecker also suggested that the whole idea of a sudden marine die-off 2.6 million years ago may be an artifact of gaps in the fossil record, rather than the result of some "cataclysm" like a supernova.

As for the great whites, if they know what killed the giant megalodon, they aren't telling.

Originally published on Live Science.