Megalodons Were Warm-Blooded—and It Was a Blessing and a Curse

Between 3.6 million and 23 million years ago, behemoth sharks that could grow roughly 50 feet long prowled the world’s oceans. But after their long reign as apex predators, these massive creatures, known as megalodons, disappeared from the face of the Earth.

For years, scientists have asked how and why megalodons got so big—and wondered what led to their demise. But now, a new finding may provide the answers to both questions: Megalodons were likely warm-blooded, at least in some parts of their bodies, according to a new paper published Monday in the journal Proceedings of the National Academy of Sciences.

This makes sense based on past research, because sharks with warmer body temperatures are able to balloon in size, like the megalodon did. Being warm-blooded likely allowed the creatures to swim faster and gobble up bigger prey, reports New Scientist’s Sofia Quaglia. However, these same advantages likely left the sharks vulnerable to environmental changes and could have led to their extinction during the Pliocene.

Scientists gleaned all this from chemically analyzing fossilized megalodon teeth found in the North Atlantic and North Pacific oceans. They looked at two isotopes, or different versions of elements, found in the teeth and noted that the pair—called carbon-13 and oxygen-18—was frequently clumped together. This suggested the teeth formed at warmer temperatures.

Researchers had previously used this technique to study warm-bloodedness in dinosaurs. The new findings suggest it’s also a handy method for studying marine vertebrates such as sharks, as study co-author Kenshu Shimada, a paleobiologist at DePaul University, tells Live Science’s Jennifer Nalewicki.

From this analysis, the team extrapolated that the megalodon’s average overall body temperature was roughly 80.6 degrees Fahrenheit, which would have been about 12 degrees warmer than oceans at the time. But that’s just an average: More than likely, some parts of the megalodon’s body were warmer than others, such as its brain, its eyes and the area around its digestive system. Scientists call this being “regionally endothermic.”

Today, the majority of sharks are cold-blooded. But a handful of them—including great white sharks, thresher sharks and mako sharks—are regionally endothermic, just like the megalodon was.

For the prehistoric shark, producing body heat in cool waters would have taken a lot of energy, even though the creature warmed just a few parts of its body. To use its metabolism to generate heat, the megalodon would have needed to eat a lot—possibly up to 100,000 calories a day. When food was abundant in the oceans, that wasn’t a problem. But when the climate began to shift and the Earth’s temperature dropped—which caused sea levels to plummet—the megalodon might have been simply unable to find enough to eat.

Declining sea levels near the end of the Pliocene would have made it more difficult for the mega-shark’s prey—calorie-dense animals like marine mammals—to survive, sending a ripple effect up the food chain to the apex predator. Even a “slight shift” in the megalodon’s main prey could have spelled trouble for its survival, as study co-author Michael Griffiths, a biologist at William Paterson University, tells National Geographic’s Riley Black.

“The biggest and scariest creatures are not necessarily the ones that are the strongest in evolutionary terms,” says co-author Robert Eagle, a biologist at the University of California Los Angeles, to New Scientist.

The new paper doesn’t answer every question surrounding the megalodon, but it does give scientists a clearer view of how this fearsome predator fared in prehistoric oceans.

“While different scientists will still argue about megalodon’s maximum possible size and what it looked like… I think it’s much more important to emphasize that we actually know a lot about this giant shark’s biology and ecology now,” says Jack Cooper, a paleontologist at Swansea University in Wales, who was not involved in the new study, to National Geographic.

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Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.