Everyone knows that dinosaurs were just giant lizards, which have cold blood. Right? According to a report from Business Standard, a new study reveals that dinosaurs weren’t so one-dimensional. Some species had the ability to raise their body temperature using external heat sources like the sun, enabling them to expend large amounts of energy and sprint after their prey.

Scientists from the University of California, Los Angeles have discovered that at least a few dinosaur species had the ability to raise their body temperatures, and were probably much more lively than modern-day alligators and crocodiles, whose massive bursts of energy last only a few seconds.

The study showed that some dinosaur species did in fact have lower body temperatures, which probably resulted in them being much less active. Some species even had lower body temperatures than modern day birds.

The scientists, led by Robert Eagle, a professor in the department of earth, planetary and space sciences at UCLA, studied a collection of fossilized eggshells that came from Argentina and Mongolia to try and determine the temperature at which the eggs formed.

By examining the chemical composition of the eggs, researchers were able to pinpoint the temperature at which it developed inside the female dinosaur. This, conceivably, would be the same as her body temperature as she was ovulating, giving researchers a read on the species’ body temperature as a whole.

The shells from Argentina, which are roughly 80 million years old, come from long-necked dinosaurs called sauropods. The eggs from Mongolia, found in the Gobi Desert, were an estimated 75 million years old, and are believed to come from oviraptorid theropods.

The sauropods were gigantic dinosaurs, and their body temperatures hovered around an estimated 37 degrees Celsius. The oviraptorid theropods were much smaller than the sauropods, and had a body temperature that likely stayed below 32 degrees Celsius.

Unlike modern mammals, which are endotherms, dinosaurs needed to get their body heat from external sources like the sun or warm surfaces that had absorbed heat earlier on. Most reptiles are ectotherms, or cold-blooded animals. According to the researchers, some of the dinosaurs may have been able to produce a little bit of internal body heat with the help of an external source.

Oviraptorid theropods were more likely to have a combination of internal and external body heat keeping their temperatures steady, but they still didn’t maintain a temperature that was as high as modern birds.

If dinosaurs were actually able to create their own body heat, they were probably able to run around and chase prey actively.