Before I tell you about the interesting discovery related to Tyrannosaurus rex, I need to review something we studied last semester - the difference between what are commonly called cold-blooded and warm-blooded animals. In warm-blooded animals, birds and mammals, for example, the body temperature normally stays within a narrow range, no matter what the outside temperature is. As a result, a warm-blooded animal is usually active in both cold and hot weather because its body temperature can adjust to the temperature of its environment. On the other hand, cold-blooded animals, such as most reptiles, amphibians, and insects, are unable to create enough heat internally to raise their temperature above the temperature of the environment. So, for example, the temperature of a cold-blooded animal falls when the environment is cool. I hope this distinction is clear. Now, moving on to Tyrannosaurus rex, you may know that dinosaurs, being reptiles, are generally believed to have been cold-blooded. Well, a recent research study found that the chemical composition of the bones of Tyrannosaurus rex was consistent with the bones of an animal that has a very narrow range of internal temperature, indicating that it was probably warm-blooded.