Given that dinosaurs have been gone for millions of years, no paleontologist has ever managed to take a dinosaur's temperature. As a result, researchers have had to surmise whether dinosaurs were warm- or cold-blooded based on fossil evidence.
Most dinosaurs were once believed to be slow-moving, cold-blooded creatures similar to today's reptiles. However, recently published research suggests that dinosaurs may have been warm-blooded.
A study in 2012 showed that growth lines on fossilized dinosaurs bones, once touted as evidence of dinos' cold-bloodedness, indicates the opposite. As LiveScience's Jennifer Welsh explained: "During slow-growing times like during the winter, they are darker and narrower, while in fast-growing times the bones have lighter, wider bands." Constant growth would indicate a warm-blooded animal, while varied growth, which appears in dinosaur bones, would suggest a cold-blooded creature.
The study's authors demonstrated, however, that even mammals can display interrupted bone growth depending on environmental conditions, such seasonal rainfall and temperature cycles, and physical considerations, such as animal's core body temperature and resting metabolic rate.