GIGANTOTHERMY

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One argument against warm-blooded dinosaurs suggests that large dinosaurs such as the sauropods would not need to be warm-blooded as their size would prevent temperature fluctuations. Heat production is related to body mass, while heat loss is related to body area. As an animal gets larger, its body area decreases relative to its body mass, so heat loss decreases and it becomes more efficient at maintaining body temperature. This theory, termed 'gigantothermy', together with the possible aid of plates, spikes, frills or nasal cavities used as heat exchangers , proposes that large dinosaurs living for the most part in a warm environment could in fact have found the body temperature of a fully warm-blooded animal thermally stressful and disadvantageous.
There are a number of counter-arguments. Although gigantothermy provides for increased efficiency of temperature regulation, it is still far less efficient than true warm-bloodedness (6 - 8 degrees C variation instead of 1 -2 degrees), and warm-blooded animals would still be expected to win easily in any evolutionary competition. Gigantothermy also does not address the problem that all dinosaurs arose initially from relatively small ancestors, certainly too small for gigantothermy to have any impact. If these small ancestors had developed warm-bloodedness and thus competed effectively with the mammals for domination, why would evolution produce giant descendants that had lost the ability? The proposals regarding sails, plates and various other ' heat exchangers ' suffer from the observation that quite closely related species , both warm- and cold-blooded, may or may not have had these additions. If they were important and obligatory for heat regulation, all species should have had them. It seems at present that these developments were probably evolved as display organs rather than heat exchangers .

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