Figure 4. Field metabolic rate plotted vs. body size. Field metabolic regressions of Nagy (1987) for modern animals extended to dinosaurian body sizes. A hypothetical dinosaurian regression is placed midway between the eutherian and lizard regression lines. Note that the avian regression line intersects the dinosaurian regression line between 6000-8000 kg. The yellow box and red box represent the method of comparing body sizes of individuals with equivalent metabolic rates. Thus, an 8000 kg animal with an intermediate metabolic rate (yellow) would have the same metabolic requirements of a 1000 kg eutherian mammal whereas an 8000 kg reptilian ectotherm (red) would have the same metabolic requirements as a 200 kg mammal.