An upper tooth from a megalodon (right) dwarfs that of a white shark. Credit: Harry Maisch/Florida Gulf Coast University
Key Points:
- Isotope analysis has revealed megalodon was warm-blooded.
- This study is the first empirical evidence of warm-bloodedness in the extinct shark.
- This warm-bloodedness may have led to its downfall, however, as it took more energy to stay heated in the cooling climate of the oceans during the Pliocene Epoch.
The largest marine predator that ever lived was no cold-blooded killer. Well, the megalodon was indeed a killer, but a new study provides the first empirical evidence of warm-bloodedness in the extinct shark. Interestingly, it’s this warm-bloodedness that may have led to the megalodon’s extinction.
The scientists looked for answers in the megalodon’s most abundant fossil remains: its teeth. In the study, published in PNAS, researchers analyzed isotopes in the tooth enamel of the ancient shark, which went extinct about 3.6 million years ago. They used a novel geochemical technique, involving clumped isotope thermometry and phosphate oxygen isotope thermometry.
“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,” said Randy Flores, a UCLA doctoral student and fellow of the Center for Diverse Leadership in Science. “Because teeth form in the tissue of an animal when it’s alive, we can measure the isotopic composition of fossil teeth in order to estimate the temperature at which they formed and that tells us the approximate body temperature of the animal in life.”
The study results showed the megalodon had body temperatures significantly higher than sharks considered cold-blooded or ectothermic, consistent with the fossil shark having a degree of internal heat production as modern warm-blooded animals do. Among the modern-day sharks with regional endothermy is a group that includes mako and great white sharks with the previously reported average body temperature ranging from 22.0 to 26.6 C, which may be 10 to 21 C higher than ambient ocean temperature. Meanwhile, megalodon had an overall average body temperature of about 27 C.
Its warmer body allowed megalodon to move faster, tolerate colder water and spread out around the world. But it was that evolutionary advantage that might have contributed to its downfall. The megalodon lived during the Pliocene Epoch, which began 5.33 million years ago and ended 2.58 million years ago, and global cooling during that period caused sea level and ecological changes that the megalodon did not survive.
“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 when it may have even had to compete against newcomers such as the great white shark,” said Flores.