Did dinosaurs have the same “secret to keeping warm” as we do?

Scarves, gloves, heating blankets, hot pot water... Various "warmth-keeping artifacts" are standard in winter, but they are the supporting role of our body's "warmth preservation". Regardless of winter or summer, our body temperature is maintained at 36 or 37 degrees Celsius. Traveling back to billions of years ago, did dinosaurs maintain their body temperature in the same way as we do? Recently, at the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, Associate Researcher Zhao Qi showed reporters a small box filled with dinosaur bone tissue slices, in which the dinosaurs' "warmth-keeping secret" was.

Small theropod dinosaur bone tissue slice. Photo by Xinhua News Agency reporter Zhang Xiaojie

Zhao Qi introduced that if the middle section of the dinosaur limb bone is sliced ​​to a thickness of about 50 microns, the secrets can be "decoded" through a microscope. Although dinosaurs are nicknamed "big lizards" by many people, some structures in dinosaur bone tissue are surprisingly more similar to humans than typical reptiles such as lizards and crocodiles.

Zhao Qi showed reporters the bone tissue structure diagrams of dinosaurs, crocodiles and humans. "We call this kind of 'small circle' a secondary bone unit, also called the Haversian system. There are many dense 'small circles' in the bone tissue of large dinosaurs and humans, but crocodiles do not have them." He explained that the Haversian system represents a higher metabolic rate. This helps researchers determine that dinosaurs are likely not like ectothermic animals such as crocodiles and lizards, which rely on "external aid" to increase their body temperature through external heat, but are closer to endothermic animals such as humans and birds, which are "good at maintaining their body temperature" and can maintain a stable body temperature.

The left, middle and right pictures are the bone tissue structures of crocodiles, large herbivorous sauropod dinosaurs and humans. The "small circles" in the middle and right pictures are Haversian systems. Photographed by Xinhua News Agency reporter Zhang Xiaojie/Map

Scientists have estimated the body temperatures of some dinosaurs using isotope methods. For example, the body temperature of Titanosaur was 38 degrees Celsius, while that of Oviraptor was 32 degrees Celsius. Zhao Qi introduced that by analyzing the surrounding rocks of the Oviraptor fossils, scientists confirmed that the ambient temperature at that time was about 26 degrees Celsius. "Normally, if an animal can stably maintain its body temperature at least 5 degrees Celsius higher than the ambient temperature, it can be considered a relatively typical endothermic animal," Zhao Qi said.

With their body temperatures higher than the ambient temperature, dinosaurs achieved a series of "achievements." "For example, some small dinosaurs incubated eggs, which first required them to have a higher body temperature. Dinosaur fossils found in Antarctica also show that dinosaurs were widely distributed, far more than reptiles that were mostly distributed in tropical and subtropical areas," Zhao Qi said.

The high metabolic rate also added a different kind of "trouble" to the dinosaurs. Zhao Qi explained that under normal circumstances, endotherms and ectotherms of the same size and body temperature consume 6 to 10 times more energy than the latter. This forced the dinosaurs to spend a lot of time eating. "Some large herbivorous dinosaurs may have started eating as soon as they woke up," Zhao Qi said.

Whether dinosaurs are endotherms or ectotherms is not only related to the dinosaurs themselves, but also an important aspect for scientists to study the evolution of vertebrates. "Today's birds evolved from dinosaurs. Their evolution and that of mammals, including humans, are two different lines, but they all eventually evolved into endotherms. Interestingly, the evolutionary processes of the two have many similarities. For example, they initially achieved a rise in body temperature by becoming gigantic, but eventually these gigantic animals became extinct." Zhao Qi said that the animals that truly evolved into endotherms are all miniaturized animals. What are their tricks for "keeping warm"? "Small mammals keep warm with hair, and some small dinosaurs have feathers, which they use to keep warm," he said.

Text reporter: Zhang Xiaojie, Zhang Quan

Video reporter: Zhang Xiaojie

Planning/Editing: Gemdale