As the largest-ever marine predator, the megalodon shark made infamous by Hollywood, measured up to 50 feet in length and was surprisingly warm-blooded, according to a new study published in Proceedings of the National Academy of Sciences.
This keen adaptation allowed the “meg” to venture into cold waters and extend its range, but paradoxically, it also bled off crucial energy, which may have contributed to the species’ extinction.
Insight From Its Large Teeth
The shark left behind long teeth that now make up the bulk of its fossil record, and the researchers analyzed those to determine how the animals responded to cold waters and frigid times.
They narrowed in on a tooth mineral called apatite, which contains isotopes of carbon and oxygen that reflect the temperature the shark’s body had maintained under harsh conditions. The megalodon would have seen plenty as it went extinct about 3.6 million years ago during the Pliocene Epoch, a time that saw oceans cool and bring about widespread ecological changes.
“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,” says Randy Flores, a fellow at the Center for Diverse Leadership in Science, in a press release.
Endotherm or Mesotherm?
To better confirm the shark’s temperature, however, they collected teeth from megalodons and other sharks, from five locations around the world, and analyzed those as well. No matter the water temperature in those areas, the megalodon showed an impressive ability to keep a steady body temperature – it consistently hovered about 13 degrees above the surrounding water.
The central question was whether the megalodon was mesothermic or truly endothermic, as humans are. Many sharks store heat generated in their muscles, making them mesothermic, meaning they hold onto warmth but mostly lack a central means of thermoregulation. We humans, by contrast, tightly control our body temperature through the hypothalamus, a region in the brain.
With the tooth data, the researchers concluded that the megalodon had been endothermic, after all, and had benefitted greatly from the ability. Such thermoregulation had allowed the shark to move faster and spread out around the world, but the energy cost made it more vulnerable to ecological pressures.
Why Did the Megalodon Go Extinct?
“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,” says Flores.
The researchers now hope to use a similar methodology to study other species.
“Having established endothermy in megalodon, the question arises of how frequently it is found in apex marine predators throughout geologic history,” says Aradhna Tripati, a professor at UCLA, in a press release.