Most scientists, paleontologists and other experts believe from the fossil evidence that megalodon became extinct over 2 million years ago during the Plio-Pleistocene period, but some cryptozoologists and researchers think that this giant shark may still exist in the undiscovered depths of the ocean. For those who accept megalodon's extinction, one theory puts changes in climate and shifts in the continents as the cause. Another suggests that that large predators like orcas and great whites could have preyed on juvenile megalodons, decreasing their chance for survival to adulthood. Megalodon expert Gordon Hubbell theorizes that the megalodon's diminishing food sources could have also been responsible for its demise -- as whale populations disappeared from tropical waters, the megalodon began to disappear, too.
Proponents of the theory of megalodon's continued existence often point to eyewitness accounts to debate the possibility of the species' survival. Occasionally, a report will surface about a large, unidentified shark in the ocean, but those accounts have been mostly discounted as tall tales. Some researchers say that the discovery of new, unfossilized teeth proves that megalodon lives, but zoologist and cryptozoology expert Ben Speers-Roesch explains that these reports are erroneous and ignore the fact that no truly unfossilized teeth have ever belonged to megalodon.
Some cryptozoologists also use examples of other recent discoveries of new species as a final point in this debate, citing the discovery of the deep-sea megamouth shark (Megachasma pelagios) in 1976. While new discoveries like the megamouth do show that we have yet to explore all that our oceans hold, scientists say it's difficult to draw a comparison from marine animals that live in the depths of the ocean and generally feed on plankton to the coastal megalodon, which was a carnivore, not a planktivore. Most scientists agree a shark of this magnitude would most certainly have been discovered by now if it were still living in its natural habitat.