Were dinosaurs warm- or coldblooded? New data suggests that the answer might be a simple “yes.”
Back in the day, paleontologists assumed that dinosaurs were all lizard-like, and had the slow metabolisms to match — making them coldblooded, like alligators. These kinds of animals, more formally known as ectotherms, have to get most of their body heat from their environment. Endotherms, like humans and other mammals, are capable of producing most of the heat they need internally.
Now we know that many dinosaurs were actually bird ancestors. Birds are endothermic, and have super-fast metabolisms.
So did some dinosaurs have birdlike metabolisms, and the hot blood to match? A study published Tuesday in Nature Communications claims to have found the answer in fossilized eggshells.
The basic findings line up with what most recent research in the area has concluded: Dinosaur metabolisms were all over the place.
“It’s important to realize that there’s actually a whole sliding scale of physiology,” even in the modern animal kingdom, study author Robert Eagle of the University of California told The Post. Birds have metabolic rates that put humans to shame, he explained, making them arguably more “warmblooded” than we are. And then you have critters like sloths, that are on the slowest, coolest end of the warmblooded spectrum. “So the real question is where dinosaurs fell on that spectrum,” he said.
That’s where Eagle’s work comes in. He and his colleagues analyzed the chemical makeup of ancient eggshells, using a technique previously perfected on teeth to estimate the temperature of the body they formed in. By measuring the abundance of chemical bonds between two rare, heavy isotopes in calcium carbonate minerals, scientists can estimate body temperature. A mineral that forms at colder temperatures will have more of these bonds than the same mineral formed at a higher temperature. In the case of an egg, scientists can use this ratio to estimate the temperature of the mother’s body when she formed it.
Eagle and his colleagues tested fossilized eggs. Many showed signs of decay that would alter any conclusions about temperature, but they were able to analyze two species successfully — and found signs of a range of metabolic rates.
One was a long-necked titanosaur sauropod, and it indicated a maternal body temperature of about 100 degrees, comparable to large mammals today. Another species — a T. rex-like oviraptorid — indicated a cooler 90-degree body temperature, which is lower than most modern mammals.
But chances are that both of them were at least somewhat endothermic, Eagle explained.
“We can’t take just body temperature and jump to the conclusion that they weren’t coldblooded,” Eagle said, “but combined with other data, it’s consistent with them having some kind of intermediary metabolism. This suggests that maybe they were warmblooded, but hadn’t developed the high level of temperature regulation seen in mammals and birds today.”
