Researchers presenting at the annual meeting of the American Geophysical Union (AGU) may have figured out what was responsible for killing off one of the mightiest sea creatures we've ever seen, the megalodon, 2.6 million years ago – rising ocean temperatures. 

Megalodons are the largest sharks to have graced the planet, blowing Jaws out the water. Individual sharks could reach lengths of 18 meters (60 feet), which – to put into some perspective – is the size of two London buses side-by-side. And their teeth alone were roughly the same size as a human hand. Yet, despite their monstrous size and nightmarish teeth, the species was no match for the global warming that occurred towards the end of the Pliocene Era. 

Megalodon was previously thought to be part of the Lamnidae family and known as Carcharocles megalodon, making it closely related to great whites, but now scientists are in agreement it belonged to the extinct Otodontidae family and is now known as Otodus megalodon.

For the study, scientists compared the internal body temperature of megalodons to those of ancestors of sharks living today, the makos and great white included. To do so, they used geochemical techniques to analyze the carbon and oxygen isotopes in their teeth. Because the bonds the isotopes form depend on the specimen's temperature as the teeth are growing, they can use fossilized teeth to estimate its average body temperature.

It also helps that teeth fossils are relatively common. Not only are they the hardiest part of the skeleton, sharks routinely shed their gnashers. This means the seabed is littered with teeth belonging to various species of shark, both alive and dead. 

The researchers found that the average body temperature of a megalodon could have been as high as 35 to 40°C (95 to 104°F) – much higher than those of makos and great white ancestors, which they found averaged 20 to 30°C (68 to 86°F).

So, what does this mean in practical terms? It means they would have had an extremely high metabolism that would have needed to be constantly fed. This would have made them especially vulnerable to rising sea temperatures and the subsequent migration of prey to cooler waters. A lethal combination of food scarcity and competition from younger species like the orca could have been their undoing.

Palaeontologists estimate that roughly a third of all large marine mammal species (including 43 percent of turtles and 35 percent of seabirds) perished around the time the megalodon faced extinction. At the same time, filter-feeding (or baleen) whales evolved to fill the gaps. 

And despite what some parts of the Internet is primed to think, there really is very little evidence to suggest this giant monster of a shark is still lurking in the oceans today. Not only are there no fossils younger than 2 million years old, there is no visible evidence (like gigantic teeth marks on smaller animals) to back this "theory" up.