LiveScience explains that we’re mostly familiar with two types of creatures. Cold-blooded animals (usually reptiles) never have a constant body temperature; it depends on their environment. Warm-blooded animals, on the other hand, retain heat to maintain a constant temperature (in humans that temperature is 98.6 degrees Fahrenheit).
Dinosaurs being reptiles, scientists assumed for many years that the prehistoric creatures were cold-blooded, or ectothermic. There was only one problem — birds are actually modern-day dinosaurs, and warm-blooded.
As it turns out, dinosaurs forged a kind of middle path — they’re neither ectothermic (cold-blooded) nor endothermic (warm-blooded) but instead mesothermic. A mesothermic creature retains some heat so that it is always warmer than the environment, but it does not maintain a constant temperature.
To arrive at these findings, published in the June 13 issue of Science, researchers examined the placement of bones in fossils to determine how quickly the bones grew, The practice is similar to examining rings in the wood of a tree to see how old it is. They also examined metabolic rates — a warm-blooded mammal that grows 10 times faster than a cold-blooded reptile also metabolizes 10 times faster.
Researchers eventually realized that dinosaurs resembled neither reptiles nor mammals, and could not be cold-blooded nor warm-blooded.
“What I’m suggesting is neither,” said John Grady, an ecologist at the University of New Mexico and author of the study. “Rather, they took a middle way – kind of like Goldilocks. And it seemed to work out very well for them.”
While mesotherms are rare, there are plenty of modern examples of the neither-here-nor-there creatures including the great white shark, tuna, leatherback sea turtle and echidna.
Being mesothermic allowed dinosaurs to grow faster than its cold-blooded rivals, which suggests why dinosaurs were able to dominate their surroundings until they went extinct 65 million years ago.
