Megalodon Endothermy Hypothesis: A new study provides the first empirical evidence of warm-bloodedness in the extinct shark.

The latest research shows that the huge Megalodon, also known as the “megatooth shark,” had a high body temperature. Existing between 23 million and 3.6 million years ago, this formidable creature measured approximately 50 feet in length.

The findings of the study were published today in the journal Proceedings of the National Academy of Sciences.

The study, initiated and led by Michael Griffiths and Martin Becker, esteemed professors of environmental science at William Paterson University, used fossilized teeth as evidence to demonstrate that the Megalodon’s body temperature was considerably higher than previously estimated.

Additionally, this research involved the collaboration of Kenshu Shimada, a paleobiologist from DePaul University in Chicago, along with Robert Eagle from the University of California, Los Angeles, and Sora Kim from the University of California, Merced. Other contributing authors include researchers from Florida Gulf Coast University in Florida, Princeton University in New Jersey, and Goethe University Frankfurt in Germany.

Earlier studies had proposed that the Megalodon, formally known as Otodus megalodon, likely possessed warm-blooded traits, specifically regional endothermy, akin to some present-day sharks. However, these conclusions were primarily based on theoretical deductions, as noted by the authors. The present study furnishes the first empirical evidence supporting the warm-blooded nature of this extinct shark.

The research team employed an innovative geochemical technique involving clumped isotope thermometry and phosphate oxygen isotope thermometry to examine the “Megalodon Endothermy Hypothesis.

“Studies using these methods have shown them to be particularly useful in inferring the thermo-physiologies of fossil vertebrates of ‘unknown’ metabolic origins by comparing their body temperature with that of co-occurring fossils of ‘known’ metabolisms,” remarks lead author Griffiths.

Clumped isotope thermometry utilizes the thermodynamic preference of certain isotopes, such as carbon-13 and oxygen-18, which have extra neutrons in their nuclei, to form bonds within a mineral lattice based on the temperatures during mineralization. The degree to which these isotopes bond or “clump” together can then provide insights into the temperature at which the mineral formed. On the other hand, phosphate oxygen isotope thermometry operates on the principle that the ratio of stable oxygen isotopes (oxygen-18 and oxygen-16) in phosphate minerals is dependent on the temperature of the body water from which they originated.

The recent study discovered that the Megalodon exhibited significantly higher body temperatures compared to sharks classified as cold-blooded or ectothermic. This finding aligns with the notion that the fossilized shark possessed a certain level of internal heat production, similar to modern warm-blooded animals. Among the present-day sharks displaying regional endothermy are species like mako and great white sharks, which were previously reported to have average body temperatures ranging from 22.0 to 26.6˚C, potentially 10 to 21˚C higher than the surrounding ocean temperature. The new study suggests that the Megalodon maintained an overall average body temperature of approximately 27˚C.

Although Otodus megalodon has left behind a rich fossil record, its biology remains poorly understood, much like many other extinct sharks, as complete skeletons of these cartilaginous fish are absent from the fossil record. Fortunately, their abundant teeth serve as a gateway to unraveling the mysteries of the past.

“Otodus megalodon was one of the largest carnivores that ever existed and deciphering the biology of the prehistoric shark offers crucial clues about the ecological and evolutionary roles large carnivores have played on marine ecosystems through geologic time,” adds Shimada.

The capacity of Otodus megalodon to regulate its body temperature holds immense evolutionary significance, as the evolution of warm-bloodedness is believed to have played a crucial role in driving its colossal size. Previous geochemical studies conducted by Griffiths, Becker, and their team have indicated that Otodus megalodon occupied a prominent position as a formidable apex predator, positioned at the pinnacle of the marine food chain.

The researchers suggest that the substantial metabolic demands required to sustain warm-bloodedness may have played a part in the species’ eventual extinction.

“Because megalodon went extinct around the time of extreme changes in climate and sea-level, which impacted the distribution of and the type of prey, our new study sheds light on the vulnerability of large marine apex predators, such as the great white shark, to stressors such as climate change,” adds Griffiths, highlighting the need for conservation efforts to protect modern shark species.

Source: 10.1073/pnas.2218153120

Image Credit: ALEX BOERSMA/PNAS