Warm Blooded Mega Shark

Based on isotopic studies of the remains of C. Megaladon, it appears that the largest shark that ever existed could maintain a relatively constant body temperature regardless of the outside water temperature.

This is not unknown among fish, a number of fish, including Great White Sharks and Bluefin Tuna, still have this ability:

The largest shark alive today, reaching up to 20 meters long, is the whale shark, a sedate filter feeder. As recently as 4 million years ago, however, sharks of that scale likely included the fast-moving predator megalodon, famous for its utterly enormous jaws and correspondingly huge teeth.

Because of incomplete fossil data, we're not entirely sure how large megalodon was and can only make inferences based on some of its living relatives, like the great white and mako sharks. But thanks to some new research on its fossilized teeth, we're now fairly confident that it shared something else with these relatives: it wasn't entirely cold-blooded and apparently kept its body temperature above that of the surrounding ocean.

Most sharks, like most fish, are ectothermic, meaning that their body temperatures match those of the surrounding water. But a handful of species, part of a group termed mackerel sharks, have a specialized pattern of blood circulation that helps retain some of the heat their muscles produce. This enables them to keep some body parts at a higher temperature than their surroundings. A species called the salmon shark can maintain a body temperature that's 20° C warmer than the sub-Arctic waters that it occupies.

Megalodon is also a mackerel shark, and some scientists have suggested that it, too, must have been at least partially endothermic to have maintained its growth rates in the varied environments that it inhabited. But, as we mentioned, the megalodon remains we have aren't even sufficient to let us know how large the animal was, much less whether it had the sort of specialized circulatory structure needed for shark endothermy.

So, a team of researchers decided to directly test whether there were signs it regulated its body temperature using things we actually do have: its teeth.

The work relies on a phenomenon known as isotope clumping. If an environment is warm enough, the small weight differences between atomic isotopes don't matter, as the heat is warm enough to thoroughly mix isotopes within a material. But as things cool down, heavier isotopes tend to pool together, forming clumps within a material. We now have equipment that can track the distribution of isotopes within a material at high resolution, allowing a direct measure of its clumpiness. That, in turn, can be used to generate an estimate of the temperature at which the material formed.

So giant warm-blooded sharks who can hunt marine mammals because they don't suffer from hypothermic torpor.

Science and nature are wonders.