The present dominance of mammals and birds clearly demonstrates the numerous advantages that result from the ability to maintain a constant, relatively high body temperature under varied environmental conditions (homeothermy). Consequently, it is not surprising that several different mechanisms for controlling body temperatures have developed in vertebrates generally. These mechanisms utilize well-known physical and physiological processes. The physical processes may be analyzed using mathematical techniques. Here we use these techniques to investigate the effect of large size upon the body temperature of a reptile and the implications for dinosaur physiology and ecology.