Megalodon was warm-blooded – and that might have been its downfall

Fossilized teeth are most of the remains we have today of the megalodon, which makes it hard to figure out what it looked like or how it lived. But now, scientists have used those teeth to estimate the ancient shark’s body temperature, and found it wasn’t exactly a cold-blooded killer. Strangely enough, that might have contributed to its downfall.

The megalodon was a giant species of shark that ruled the oceans about 20 million years ago. Like modern sharks, its skeleton would have been mostly made of cartilage, so we don’t have fossils to tell us what it really looked like. All we do have is a pile of terrifyingly huge teeth.

But there are a few things we can figure out from those. By looking at the proportions of the teeth and comparing them to living sharks, scientists have estimated that megalodon grew to be about 15 m (50 ft) long or even longer, which is at least three times bigger than the most massive great whites.

And now scientists at UCLA have discovered new insights from megalodon teeth – their body temperature. Specific mixes of isotopes will be locked into minerals as they form, preserving a record of the environmental conditions that mineral was exposed to at the time. Analyzing this isotopic composition in an animal’s teeth can reveal details like where it lived, what it ate or, in this case, its body temperature.

“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, an author of the study. “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.”

In doing so, the researchers found that the megalodon was able to maintain a body temperature that was about 7 °C (13 °F) warmer than the water it lived in. That’s a big enough difference to class it as a warm-blooded creature, unlike most sharks. It would have done so through a process called mesothermy, where it stored heat generated by its muscles to fuel its activities. Some living sharks, such as great whites, are known to regulate their body temperature this way.

The researchers calculated the water temperature of the time by analyzing the isotope compositions of scallop shells from the same period. The megalodon teeth gave temperature readings that were consistently much higher.

Having a warmer body would have allowed the megalodon to move faster and live in colder waters, which would have helped it thrive all around the world during its time. But intriguingly, this may also have led to its eventual extinction about 3.6 million years ago, when ecological conditions are known to have drastically changed.

“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.

That’s a bit more believable an extinction story than some more dramatic hypotheses that have been thrown around before, including that a relatively nearby supernova contributed to their demise.

The research was published in the journal PNAS.

Source: UCLA