EVOLUTIONARY ASPECTS IN MAMMALS 



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v ulpecula , showed a variance of about 3 C--between 36.1 C and 



SS.e*^ C. His cats showed a variance of 1.4 C whereas the rabbits 

 showed a range of 3.6° C. Martin did what very few people do but 

 what is necessary to get intelligible results; he reported the expo- 

 sure time to the various air temperatures, and also regulated air 

 temperature both up and down while recording body temperature. 

 His exposure times ranged between 60 and 100 minutes. Martin 

 argues that the platypus has beenunjustly listed as a poikilothermic 

 animal. Between 5 G and 30 C air temperature, he claims that it 

 adjusts its body temperature even better than the rabbit. However, 

 when subjected to a temperature above 30 G, it became what Martin 

 called "feverish." Observations done by a number of naturalists on 

 the platypus indicate that its relation to the aquatic medium may be 

 important for its temperature regulation. By a closer examination, 

 it becomes apparent that body cooling is frequently attained in the 

 tropics by returningto water (Hesse, 19 37). This is particularly true 

 among larger animals, like the water buffalo, the water buck, the 

 rhinoceros, the elephant, and most strikingly, the hippopotamus. The 

 elephant also frequently operates his personal, built- in shower, and 

 his ears are of paramount importance in temperature regulation. 

 These animals have a number of interesting specialities in their 

 temperature regulation. However, the discussion of these I think be- 

 longs more properly in Dr. Morrison's paper. For the purpose of 

 my discussion, it suffices to emphasize that body cooling by return- 

 ing to water frequently occurs in tropical forms and also among the 

 more primitive ones. Gooling results not only from staying sub- 

 merged and benefiting from the larger conductivity of the water for 

 heat, but also from frequent emergence from the water and obtaining 

 a cooling effect by way of the evaporative characteristics of the air. 

 Significantly, a great percentage of the primitive forms aid their 

 less-developed temperature regulation by burrowing. Itis interest- 

 ing that the substratum temperatures in tropical Australia never 

 exceed 85 F (Vorhies, 1945). 



Martin's data on metabolic heat production shows a number of 

 interesting features. Minimum heat production was found at about 

 30 G in all the species, including the higher mammals. His fig- 

 ures, calculated according to body surface show a similar metabolic 

 rate for both the monotremes and the marsupials, which were only 

 one-third of the values he got for the higher placental mammals. 



