T. rex was one of the dinosaurs the team examined The bigger a dinosaur was, the warmer its blood, a study of the big beasts fossil remains suggests. Dinosaurs were long considered to be cold-blooded reptiles. More recently, some researchers have proposed that the extinct creatures actively regulated their body emperature like mammals.
A study in the journal Plos Biology now suggests this is not the case, but that bigger dinosaurs may have lost heat so slowly that they stayed warm anyway. Reptiles tend to be cold-blooded ectotherms, whose internal body temperature is dependent on the outside environment. For example, lizards and snakes will sun themselves on rocks in order to heat themselves up.
Birds and mammals, on the other hand, tend to be warm-blooded endotherms. They can regulate their internal body temperature regardless of external influence. Their body temperatures tend to be more constant than those of reptiles and higher than the outside environment.