The sharks that roam today’s oceans can be fearsome, but they don’t really compare to some of the species that dominated the seas millions of years ago. The Megalodon — a massive shark that is thought to have died out around 2.6 million years ago — has left plenty of fossils behind for researchers to find, but determining what exactly killed the species off has proven a big challenge.

As LiveScience reports, new research was presented recently at the annual American Geophysical Union conference that suggests the shark could regulate its body temperatures similar to some species of modern sharks. However, the ancient shark’s much higher body temperature may have been its downfall.

Determining the body temperature of an animal that hasn’t existed for millions of years is tough but not impossible. Clues to the shark’s body temperature were found in its teeth. Isotope bonds form differently depending on the temperature, and the teeth of the megalodon suggest its body temperature was very high.

The shark’s size was the key to its dominance, but it was so large that its body temperature may have rivaled that of whales. If the creature was keeping its body temperature as high as 104 degrees Fahrenheit its metabolism would likely have demanded that it consume a huge amount, and as global temperatures change, it’s likely that the sharks just couldn’t keep up.

As the shark’s prey moved to new, cooler areas, the massive predators would have felt a serious pinch. It’s also likely that new predators began to out-hunt the large sharks, putting even more strain on the  species.