The ocean is home to some of the most awe-inspiring creatures ever to exist, but few have captured human imagination quite like the megalodon. Revered as the largest predatory shark to ever roam the seas, the megalodon has often been imagined as an unstoppable, cold-blooded killer lurking in prehistoric waters. However, a new scientific analysis is painting a much more complex and fascinating picture of this ancient apex predator. Contrary to popular belief, the megalodon wasn’t cold-blooded. In fact, this gigantic predator was warm-blooded, a discovery that not only redefines our understanding of its biology but also provides crucial insight into why it vanished from Earth’s oceans about 3.6 million years ago.
In a study spearheaded by environmental scientists from UCLA, UC Merced, and William Paterson University, researchers analyzed isotopes in megalodon tooth enamel and uncovered surprising findings. Published in the journal Proceedings of the National Academy of Sciences, the study shows that the megalodon maintained a body temperature roughly 13 degrees Fahrenheit (about 7 degrees Celsius) warmer than the surrounding ocean water. That thermal difference is significant—greater than what is seen in other ancient sharks that coexisted with the megalodon—and places this predator in the category of warm-blooded animals, or at least animals capable of endothermy.
This discovery holds profound implications not only for understanding the life and extinction of megalodon but also for drawing parallels to modern-day marine predators. It suggests that the massive energy expenditure required to sustain a warm body temperature may have played a critical role in the shark’s extinction, and raises questions about how today’s ocean giants may fare in an era of climate change.
For years, paleontologists and marine biologists have debated whether the megalodon was endothermic. Modern sharks in the same mackerel shark family, such as the great white and the thresher shark, exhibit traits of mesothermy and regional endothermy—meaning they can keep parts of their bodies, like their muscles or stomachs, warmer than the surrounding water. But they aren’t fully warm-blooded in the way mammals are. The megalodon, however, seems to have taken this ability to a new level.
Lead researcher Robert Eagle, a UCLA assistant professor of atmospheric and oceanic sciences and a member of the UCLA Institute of the Environment and Sustainability, explained the importance of these findings. “Studying the driving factors behind the extinction of a highly successful predatory shark like megalodon can provide insight into the vulnerability of large marine predators in modern ocean ecosystems experiencing the effects of ongoing climate change,” Eagle said. In other words, understanding what doomed megalodon could help us protect today’s great ocean hunters.
The megalodon, whose name means “big tooth,” certainly lived up to its reputation. Estimates suggest it reached lengths of up to 50 feet—more than three times the length of a great white shark—and weighed as much as 100 tons. It ruled the oceans during the Miocene and Pliocene epochs, preying on whales, dolphins, seals, and even other sharks. As part of the Lamniformes order of mackerel sharks, megalodon’s modern relatives share similar hunting strategies and thermoregulatory adaptations, but none come close to matching its size or, as we now know, its ability to maintain an elevated body temperature.
To understand how megalodon managed this feat, the researchers turned to its most abundant and scientifically valuable fossil remains: its teeth. Unlike bones or soft tissue, which rarely fossilize well, teeth are mineral-rich and often survive for millions of years. One of the key minerals found in teeth is apatite, which contains carbon and oxygen atoms. These atoms can occur in “light” or “heavy” forms, known as isotopes. The ratio of these isotopes in tooth enamel can reveal a surprising amount about an animal’s biology and the environment it lived in.
As Randy Flores, a UCLA doctoral student and fellow of the Center for Diverse Leadership in Science, explained, “You can think of the isotopes preserved in the minerals that make up teeth as a kind of thermometer, but one whose reading can be preserved for millions of years.” When an animal is alive, its body temperature affects how these isotopes are incorporated into the enamel. So by analyzing these isotope ratios in fossilized teeth, scientists can estimate the body temperature of long-extinct animals.
For this study, the research team collected megalodon teeth, along with those from contemporary shark species, from five locations around the world. They then used advanced mass spectrometry techniques at UCLA and UC Merced to analyze the isotopic composition of the teeth. Their statistical modeling also allowed them to reconstruct the seawater temperatures in these ancient environments.
What they found was remarkable. While most sharks’ body temperatures closely match the temperature of the surrounding water, the megalodon’s teeth showed a consistent and significant temperature increase. This suggested that megalodon was producing enough metabolic heat to keep its body significantly warmer than the ocean it lived in. Such a physiological advantage would have given it the ability to swim faster, tolerate colder waters, and expand its range across the globe, making it one of the most formidable predators in Earth’s history.
But this evolutionary advantage came with a high price. Maintaining such an elevated body temperature requires a tremendous amount of energy. The megalodon would have needed to consume enormous amounts of food to fuel its metabolism. As the Pliocene epoch progressed, the Earth underwent a period of global cooling. Sea levels dropped, ecosystems shifted, and the abundance and distribution of prey likely changed dramatically. In these new environmental conditions, the megalodon’s colossal energy demands may have become unsustainable.
“Maintaining an energy level that would allow for megalodon’s elevated body temperature would require a voracious appetite that may not have been sustainable in a time of changing marine ecosystem balances,” Flores explained. Compounding the problem was competition from other emerging predators, such as the great white shark, which may have been better adapted to the evolving marine environment.
The Pliocene cooling not only reduced the available prey but may have also fragmented populations of megalodon, preventing them from accessing abundant hunting grounds. Unable to meet their immense energy needs and facing stiff competition from more versatile predators, megalodon populations likely dwindled and ultimately went extinct.
Project co-leader Aradhna Tripati, a UCLA professor of Earth, planetary, and space sciences, emphasized how this new understanding opens the door for further research. “Having established endothermy in megalodon, the question arises of how frequently it is found in apex marine predators throughout geologic history,” Tripati said. The team now plans to use similar isotopic analysis techniques to study other ancient marine species, hoping to piece together a clearer picture of how endothermy evolved and how it influenced the survival—or extinction—of major predators.
This study also holds powerful lessons for the present and future. Modern apex predators, including sharks, whales, and large fish, face mounting threats from human activity, habitat loss, overfishing, and climate change. As ocean temperatures shift and ecosystems are disrupted, these species may find it harder to secure enough food to sustain themselves, much like the megalodon millions of years ago. Understanding the fate of ancient predators like megalodon may help scientists anticipate how today’s marine giants might adapt—or fail to adapt—to similar challenges.
The megalodon’s story is one of triumph and tragedy. For millions of years, it ruled the oceans as one of the most successful and powerful predators ever to exist. Its warm-blooded physiology allowed it to roam vast distances, hunt with unparalleled efficiency, and dominate marine ecosystems. Yet, in the end, this very adaptation may have hastened its downfall. Unable to cope with the rapid environmental changes of its time, the megalodon disappeared from the oceans, leaving behind only its massive teeth and the mysteries they contain.
More information: Griffiths, Michael L. et al, Endothermic physiology of extinct megatooth sharks, Proceedings of the National Academy of Sciences (2023). DOI: 10.1073/pnas.2218153120