The question of how dinosaur bodies functioned has been a controversial subject since the bones of the extinct creatures were first dug up, but it really picked up momentum around 150 years ago. Traditionally dinosaurs were assumed to have been big, lumbering cold-blooded animals, much like modern lizards and crocodiles.
But starting in the 1960s, there was a sea-change in opinion that framed dinosaurs as more active, warm-blooded creatures closely related to birds, and a new study aims to shed some light on this debate. By analyzing the chemical signatures persevered in fossil eggs, researchers were able to calculate the temperature at which they formed inside the mother.
“The state of the science at the moment is that people don’t like to think of it as a kind of cold-blooded versus warm-blooded dichotomy,” Rob Eagle, who coauthored the paper published in Nature Communications, explained to IFLScience. “In reality when you look at modern vertebrates there’s quite a spectrum of physiologies, it’s more like a sliding scale. So it’s really a question of where dinosaurs fall on that sliding scale.”
A reconstruction of a nesting oviraptor. Doyle Trankina and Gerald Grellet-Tinner
Modern, more sensitive techniques are allowing scientists to analyze the chemistry of fossils and give us new insights into how long-extinct animals looked and lived. By studying the calcium carbonate mineral that forms the shells of dinosaur eggs, and specifically the abundance of bonds that form between two rare heavy isotopes of carbon and oxygen, the researchers were able to determine the temperature at which the shells formed. Because this formation happens deep within the body of female animals, this data can therefore tell you the body temperature of the adult, says Eagle.
Before looking at the dinosaur fossils, the scientists first turned their attention to their living counterparts and relatives. They analyzed the chemistry of the eggshells of 13 living bird species and nine reptiles to create a matrix on which they could then compare the results from the fossilized eggs. They found that the colder the internal body temperature, the more bonds formed between the isotopes of carbon and oxygen and thus the more “clumped” they were.
A clutch of titanosaur eggs on the surface in Argentina. Gerald Grellet-Tinner
It’s rare to find dinosaur eggs that we know for certain are from a specific species, as it usually requires the remains of the embryo to have stayed intact inside the egg. It’s even rarer to find that the chemistry of the egg has remained unchanged during the tens of millions of years it has been preserved. But Eagle and his team found two hauls of dino eggs, one set from the giant titanosaurs of Argentina and another from small oviraptors of Mongolia, that fit this bill.
They were able to determine that the oviraptor probably had a body temperature of around 31.9 degrees Celsius (89.4 degrees Fahrenheit), whereas the titanosaur was running a little hotter at 37.6 degrees Celcius (99.7 degrees Fahrenheit). This surprised the researchers to a certain extent, because even though oviraptors are more closely related to modern birds than titanosaurs, their body temperature was apparently much lower than what we see in birds today. This is the first measurement of body temperatures in two types of dinosaur, and backs up the idea that they were neither warm nor cold-blooded, but something in between the two.
While they’ve been able to calculate what body temperature the animals were maintaining, “what we can’t determine is why their bodies were at that temperature,” Eagle told IFLScience. The titanosaur, for example, could have been warmer simply because they were such massive animals. Eagle next wants to look at the fossil eggshells of early birds to determine at what point birds gained their present-day body temperature.
