We used to think of dinosaurs as enormous reptiles, cold-blooded with scaly skin and monotone coloring. But in recent years, we’ve learned that many dinosaurs were likely covered in vibrant feathers and were more closely related to birds than any modern lizards. And many of those cold-blooded dinosaurs we thought basked in the sun to warm up, were instead warm or even hot-blooded creatures.
The journal Nature recently published a study where researchers used a novel technique to identify warm- and cold-blooded dinosaurs. Their findings tell a new story of how these creatures lived and died. Researchers analyzed fossil specimens and measured the ratio of biochemical byproducts that resulted from breathing. They then discerned which dinosaurs were warm- and cold-blooded, finding in the fossil record that warm-blooded dinosaurs would breathe more than cold-blooded.
“This metabolic symbol actually preserves quite well,” says study co-author Jasmina Wiemann, a molecular paleobiologist at Yale University.
The research showed that most dinosaurs like Plesiosaurus, Tyrannosaurus rex, Diplodocus and Allosaurus were warm-blooded, but other famous species like Stegosaurus and Triceratops were cold-blooded.
Why Does it Matter?
According to Wiemann, determining whether a dinosaur was warm- or cold-blooded provides a window into their lifestyle and habitat preference. She says we now can picture dinosaurs as creatures with more avian features — agile, full of energy and constantly in need of food. Cold-blooded dinosaurs, like Stegosaurus and Triceratops, on the other hand, had low metabolic rates, comparable to lizards. They would have needed to choose where to live accordingly.
This means that cold-blooded dinosaurs would have spent ample time basking in the sun. And when the weather warranted, they may have migrated to warmer environments to thermoregulate. But while these dinosaurs likely moved slowly, our idea of huge and lumbering dinosaurs should instead depict a nimbler creature.
“Huge sauropods faced more of a challenge in cooling down than warming up. They had active lifestyles and had to feed their metabolisms constantly,” says Wiemann. “In the end, these enormous creatures had metabolisms similar to modern birds, which still today have the highest in the animal kingdom.”
Warm- and Cold-Blooded Advantages
Warm- and cold-blooded species had their strengths and weaknesses. But it’s important to note that cold-blooded dinosaurs were more dependent on their environment, according to study co-author Matteo Fabbri, of the Field Museum in Chicago.
“It’s the same reason that you don’t find crocodiles in the Arctic. They’re dependent on the environment to regulate their own temperature,” says Fabbri.
Dinosaurs that were warm-blooded could live all over the planet because they could survive colder temperatures, he says. They didn’t need to depend on environmental changes in the weather. But this also means that they had to stay active and constantly seek out sustenance to feed their high metabolisms. Huge, warm-blooded dinosaurs would likely spend most of their time seeking out food to keep up with the energy they burned daily.
Metabolism and Mass Extinction
Scientists previously thought that part of the reason why birds escaped mass extinction was because they were the only warm-blooded species and were more agile. But this research shows that this is unlikely the case. Most of the dinosaurs and pterosaurs that died out as a result of the Cretaceous–Paleogene extinction (K–Pg) event, 66 million years ago, were also warm-blooded and agile.
“Metabolism was definitely not the selective factor that determined survival as we previously thought,” says Wiemann. “Other factors like body mass and reproductive strategies may have played a role in the bias that we see across the K–Pg extinction.”
In the end, most dinosaurs weren’t giant, oafish lizards lumbering around the landscape. They were vibrant, active, bird-like creatures constantly on the move. And according to both Wiemann and Fabbri, this is only the beginning of a new picture researchers are painting of the dinosaurs who once ruled the Earth.