The giant predator shark megalodon went extinct some 3.6 million years ago, more than a million years earlier than previously thought.

After surveying fossil data related to previous attempts to pinpoint the disappearance of Otodus megalodon, scientists realized most earlier efforts were flawed. To identify a more accurate extinction data, scientists catalogued all megalodon fossils recovered from ancient, fossil-rich deposits in California and Mexico's Baja California.

The research showed legitimate megalodon fossils can be found up until the end of the early Pliocene, 3.6 million years ago. Megalodon fossils recovered from rocks younger than early Pliocene deposits, scientists determined, either migrated from separate fossils sites or eroded from older strata.

"We used the same worldwide dataset as earlier researchers but thoroughly vetted every fossil occurrence, and found that most of the dates had several problems -- fossils with dates too young or imprecise, fossils that have been misidentified, or old dates that have since been refined by improvements in geology; and we now know the specimens are much younger," Robert Boessenecker, vertebrate paleontologist at the College of Charleston, said in a news release. "After making extensive adjustments to this worldwide sample and statistically re-analyzing the data, we found that the extinction of O. megalodon must have happened at least one million years earlier than previously determined."

Between 1 and 2.5 million years ago, several unusual marine species, including early seals, walruses, sea cows, porpoises, dolphins and whales, also went extinct. Previously, scientists linked the disappearance of megalodon with the mass extinction event. The new research -- published this week in the journal PeerJ -- suggests the demise of the ancient predator shark was unrelated.

With the timing of megalodon's disappearance shifted, scientists are now unsure whether the collection of marine extinctions constitutes a "mass extinction" designation.

"Rather, it is possible that there was a period of faunal turnover -- many species becoming extinct and many new species appearing -- rather than a true immediate and catastrophic extinction caused by an astronomical cataclysm like a supernova," Boessenecker said.

In their paper, scientists argue the arrival of the modern great white shark, Carcharodon carcharias, offers a better explanation for megalodon's downfall. The great white shark first appears in the fossil record some 6 million years ago. At first, the shark was relegated to the Pacific, but just 2 million years later, the predator had proliferated throughout Earth's oceans.

"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 -- rather than radiation from outer space," Boessenecker said.

Earlier research efforts also argued megalodon lost out to white sharks and killer whales.

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