posed to the environment; therefore, it requires more energy to maintain the positive energy balance. Student’s t-tests were used to compare differences in temperature and body size in endotherms and ectotherms, different mammalian subclasses, and in the crab. MethodsDetermining the WMR of endotherms and ectotherms-In this experiment, we found the average WMRs of a large endotherm, which was a rat, a small endotherm, which was a mouse, and an ectotherm, which was an iguana. The bottom of the metabolism chamber was covered with approximately 50 ml of soda lime, which absorbed any carbon dioxide exhaled by the animal. A thermometer was placed in the chamber for five minutes until the temperature had equalized. Each starving, resting animal was weighed and placed in the chamber. The inside of a calibrated 5-ml plastic manometer tube was wet with tap water, inserted into the hole of a rubber stopper, and then placed into the end of the metabolism chamber. The chamber was sealed by applying a drop of a soap bubble solution to the end of the manometer, and the time it took to move along the manometer was measured. For the mice and rats, we measured the time it took for the bubble to move 5 ml, five times. For the iguanas, who have much slower metabolic rates, we measured the time it took to move 1 ml, one time. Using the volume of air consumed per minute, a series of conversions were applied so that we found the WMR for each animal, correct for size and STP.Computer Simulations of Metabolic rates-We compared the metabolic rates of prototherian, metatherian, and eutherian mammals. Metabolic rates were estimated by measuring the oxygen consumption rates of representative species in the mammalian subclasses, and were corrected for body size for comparative purposes. The animals we studied were: Ornithorhyncus-a duck-billed platypus, Echidna-a spiny anteater, Bettongia-a rat kangaroo, Dasyurus-a marsupial “cat”, Tric...
