Were Dinosaurs Warm Blooded? New Tech Sheds Light on Debate

According to the team’s analyses, reported online today in Nature Communications, the egg-laying titanosaurids had body temperatures of about 37.6°C (99.7°F). This is the first time when dinosaur eggshells have been used to understand the body temperature and metabolism of dinosaurs.

Warm-blooded animals, or endotherms, produce heat internally and are able to maintain their body temperature through metabolism. Humans and other mammals fall into this category.

They found that body temperature of dinosaur differed widely. Lizards, for example, often sit on rocks in the sun to absorb heat, which enables them to be more active. Previous studies have suggested scientists can determine the difference in dinosaurs by counting the carbon and oxygen isotopes in ancient bones and teeth. The research indicates that the answer could lie somewhere in between. The dinosaurs, at least the oviraptorid theropods, had the ability to elevate their body temperature above the environmental temperature.

“The temperatures we measured suggest that at least a few dinosaurs were not fully endotherms (warm-blooded) like modern birds”, said the study’s lead author Robert Eagle of the University of California Los Angeles (UCLA), “They may have been intermediate – somewhere between modern alligators and crocodiles and modern birds”. These kinds of animals, more formally known as ectotherms, have to get most of their body heat from their environment. Birds have metabolic rates that put humans to shame, he explained, making them arguably more “warm blooded” than we are. This enabled them to estimate that the environmental temperature in Mongolia shortly before the dinosaurs went extinct was approximately 79 degrees Fahrenheit.

The discovery supports other research that dinosaurs were neither warm- nor cold-blooded, and that body temperature varied amongst species.

Eagle also noted that these findings could indicate that that they produced a few heat internally and elevated their body temperatures above that of the environment but didn’t maintain as high temperatures or as controlled temperatures as modern birds. To find out how warm the bodies were that laid the eggs, the team measured the proportions of bonds between two rare, heavy isotopes, carbon-13 and oxygen-18. But it still isn’t clear how much of the boost in body temperature comes from increased metabolism versus insulation-providing feathers or behaviors like basking in the Sunday.

Of the 32 eggshells the team analyzed, only six were considered well-preserved enough to include in their results: three from oviraptorids in modern-day Mongolia and three from titanosaurids in what is now Argentina. With a mass spectrometer, researchers might measure these isotopic bonds in fossilized eggs.

The titanosaur sauropods mother’s body temperature was around 38 degrees Celsius, or 100 degrees fahrenheit. That’s the implication for the oviraptorid theropods.

The research was funded by the National Science Foundation and UCLA’s physical sciences division.

Using a new technique for analyzing the chemical makeup of fossilized eggshells, they came to a surprising conclusion: Dinosaurs were neither warm blooded, or endothermic, nor cold blooded, or ectothermic. A novel technique suggests they might have had a foot in both camps.

Both of the species studied – titanosaurs and oviraptors – lived around 70 to 80 million years ago during the Upper Cretaceous period.

Although the research proved these dinosaurs had lower body temperatures, they were less active than their feathery friends.

Regardless, the team’s results are fairly compelling evidence that “dinosaurs were not cold-blooded tail-draggers”, says Gregory Erickson, a vertebrate paleontologist at Florida State University in Tallahassee. The isotopes – carbon-13 and oxygen-18 – tend to cluster together more closely at colder temperatures.

Now we know that many dinosaurs were actually bird ancestors. “In the case of eggshells, the abundance of these bonds reflects the body temperature of the female when the eggshell forms”.

The researchers concluded the question is not so simple as being either one or the other. Eggshells are “a new piece of evidence” that researchers haven’t tapped before, he notes. And then you have critters like sloths, that are on the slowest, coolest end of the warm blooded spectrum.

“There’s just a massive spectrum of different questions we can ask now”, he said.