Answer to Critical Thinking Activity - Chapter 6

1. No on both counts. As we use these terms, you cannot generate internal heat to moderate body temperature (endothermic) and at the same time have a fluctuating internal body temperature controlled by the environment (poikilothermic). Likewise, if you rely on the environment and behavior to control internal temperature (ectothermic), you certainly would not be maintaining a constant internal body temperature (homeothermic). However, an animal could be endothermic and homeothermic, as well as ectothermic and poikilothermic.

2. We tend to associate warm-bloodedness strictly with birds and mammals, and cold-bloodedness with reptiles right on down to the protozoa. Perhaps we should define as warm-blooded any animal that maintains a body temperature above or independent from that of the environment, and as cold-blooded any animal whose body temperature is controlled by the environment, not metabolic reactions. Remember, your opinion here is probably as good as any.

3. Respiratory turbinates are small, curved bones found in the nasal passages of most birds and mammals. They are thought to help trap part of the large amount of water exhaled by warm-blooded animals. It is presumed that, without these small bones, many warm-blooded animals could not maintain a proper internal water balance. Respiratory turbinates therefore are felt to be indicative of a warm-blooded animal. We must remember that only most, not all, warm-blooded animals have them, and their presence in dinosaurs has not been proven. Recent research has shown that some dinosaurs probably do have these bones. The question still remains as whether or not respiratory turbinates are proof of warm-bloodedness.

4. We tend to think of dinosaurs as cold-blooded because, except for the leatherback turtle and perhaps some pythons, modern reptiles are cold-blooded. This shows a certain bias because it is not proven whether or not dinosaurs were warm-blooded. Birds are well accepted to be descended from dinosaurs, and a growing number of biologists believe that birds should be reclassified as the last of the dinosaurs. Even if we do consider birds as modern day dinosaurs, just because they have warm body temperatures does not mean the ancient dinosaurs did. Endothermy could easily have come along after the birds got their start. In doing this exercise, you have read some of the evidence for either endothermy or ectothermy, and perhaps discovered more while exploring the Web. I feel that the evidence, including the respiratory turbinate discussion, for warm-bloodedness slightly outweighs that for cold-bloodedness. However, I readily admit that I would very much like for it to be proven that the dinosaurs were warm-blooded, and that certainly shows another kind of bias.