Editor’s note: Sign up for CNN’s Wonder Theory science newsletter. Explore the universe with news on fascinating discoveries, scientific advancements and more.

CNN  — 

Megalodon, one of the most fearsome sharks that ever lived, wasn’t the cold-blooded killer it’s made out to be — at least not literally.

Through an analysis of fossilized megalodon teeth, scientists have discovered the extinct shark was partially warm-blooded, with a body temperature around 7 degrees Celsius (12.6 degrees Fahrenheit) warmer than estimated seawater temperatures at the time, according to a study published last week in the journal Proceedings of the National Academy of Sciences.

“We found that O. megalodon had body temperatures significantly elevated compared to other sharks, consistent with it having a degree of internal heat production as modern warm-blooded (endothermic) animals do,” study coauthor Robert Eagle, professor of marine science and geobiology at UCLA, said in an email.

The findings suggest this distinct trait played a key role in the ancient predator’s terrifying size — and its eventual disappearance.

Gigantism in megalodon

Believed to be at least 15 meters (49 feet) long, Otodus megalodon, also known as the megatooth shark, was one of the largest apex marine predators since the Mesozoic era and went extinct about 3.6 million years ago, according to Eagle.

Scientists previously theorized that megalodons were warm-blooded, but the new study is the first to provide concrete evidence to that effect.

The researchers observed how closely carbon-13 and oxygen-18 isotopes found in the ancient shark’s fossilized teeth were bonded together — a data point that can reveal how warm the body was. From this finding, they deduced the megalodon’s average body temperature was about 27 C (80 F).

Like modern great white and mako sharks, megalodons were regionally endothermic, which means they had the ability to regulate temperature in certain parts of the body, according to the study. In contrast, the body temperatures of other cold-blooded apex predators are regulated by the temperature of water around them.

Being warm-blooded may have been one of the key drivers fueling megalodons’ massive size and overall prowess as predators, according to senior study author Kenshu Shimada, a paleobiologist at DePaul University in Chicago.

“A large body promotes efficiency in prey capture with wider spatial coverage, but it requires a lot of energy to maintain,” Shimada said in an email. “We know that Megalodon had gigantic cutting teeth used for feeding on marine mammals, such as cetaceans and pinnipeds, based on the fossil record. The new study is consistent with the idea that the evolution of warm-bloodedness was a gateway for the gigantism in Megalodon to keep up with the high metabolic demand.”

The ‘vulnerability of being warm-blooded’

For such an enormous animal, having to use so much energy constantly to regulate its body temperature may have contributed to its downfall as the world changed. The timing of megalodons’ extinction coincides with the cooling of the Earth’s temperature, the researchers said.