March 4, 2024

Fossilized teeth make up the bulk of the megalodon remains we have today, making it difficult to figure out what it looked like or how it lived. But now, scientists have used these teeth to estimate the ancient shark’s body temperature and found that it wasn’t exactly a cold-blooded killer. Oddly enough, this may have contributed to its downfall.

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

But we can figure out a few things from it. By looking at the proportions of the teeth and comparing them to extant sharks, scientists estimate that the megalodon was about 15 m (50 ft) or more in length, which is at least three times larger than the largest great white shark.

Now UCLA scientists have uncovered a new insight from the teeth of megalodon sharks — their body temperature. A specific mixture of isotopes would be locked into the mineral as it was formed, keeping a record of the environmental conditions the mineral was in at that time. Analyzing the isotopic composition in an animal’s teeth can reveal details such as 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 the readings are preserved for millions of years,” said Randy Flores, one of the study’s authors. “Because Teeth form in the tissues of animals while they are alive, so we can measure the isotopic composition of fossil teeth to estimate the temperature at which they formed, which tells us the approximate body temperature of the animal during life.”

In doing so, the researchers found that the megalodon is able to maintain a body temperature about 7 °C (13 °F) warmer than the water it inhabits. This difference is large enough to classify it as warm-blooded, unlike most sharks. It does this through a process called mesotherm, in which it stores the heat generated by the muscles to fuel its activities. Some extant sharks, such as the great white, are known to regulate their body temperature in this way.

The researchers calculated the water temperature at that time by analyzing the isotopic composition of scallop shells from the same period. The temperature readings given by the megalodon teeth were consistently much higher.

Having a warmer body would have allowed the megalodon to move faster and live in cooler waters, which would have helped it thrive around the world at the time. But interestingly, this may also have contributed to its eventual extinction around 3.6 million years ago, when ecological conditions had changed dramatically.

“Maintaining the megalodon’s elevated body temperature requires a voracious appetite, which may not be sustainable in an era of changing marine ecosystem balance, as it may even have to compete with newcomers such as the great white.” Lores said.

This is a more believable extinction story than some of the more dramatic hypotheses put forward before, including that a relatively recent supernova caused their demise.

The study was published in the journal Proceedings of the National Academy of Sciences.

source: UCLA