EVOLUTIONARY ASPECTS IN MAMMALS 



However, all theirspeciesofPhalangeridae achieved thermal equili- 

 brium at an air temperature of 40 C. The carnivorous marsupials 

 seemed to be particularly vulnerable at the 40 C air temperature. 

 Most of the species showed increased respiratory rates at the high 

 air temperatures. Also open- mouth panting, and salivation and coat 

 licking in typical postures promoting heat dissipation frequently 

 appeared. The Tasmanian devil ( Sarcophilus harisii), was an 

 exception and showed no reaction other than an increase in water 

 consumption. The authors point to the fact that the species unable 

 to maintain equilibrium at 40 C were all among the most phylo- 

 genetically primitive. The author's attempt to classify the ability 

 among mammals to dissipate heat is shown in Tables I and II, 

 which are taken from their work. 



Bartholomew (1956) has presented perhaps the only detailed 

 study of the various facets of temperature regulation in a marsu- 

 pial. He made careful studies of the macropod(Setonix brachyurus ) 

 both under laboratory conditions and in the field. He recorded a 

 considerable diurnal lability in body temperature related to the 

 daily cycle of activity in the field. The species studied showed a 

 typical nocturnal activity pattern, and the day-time rectal tempera- 

 tures of 37 C were significantly lower than the night-time tem- 

 peratures. It is important that the slight excitement occurring dur- 

 ing attachment of thermocouples could cause temporary elevations 

 of body temperature up to 1.5 C in the rectal temperature. Upon 

 the exposure to high air temperatures (40 C), a copious secretion 

 of saliva and licking of the feet and tail, and a distinct vasodila- 

 tion of peripheral parts seem responsible for maintenance of ther- 

 mal balance at these high air temperatures. The increase in res- 

 piratory rate was appreciable, up to 200 per minute, but never as 

 vigorous as, for instance, panting in a dog. When the animals were 

 returned to room temperatures of 20 C there were indications 

 that the peripheral vasodilation persisted for some time after 

 removal of the heat stress. The elevation of the deep-body tem- 

 perature during the heat load seemed moderate and did not exceed 

 1 G. At extreme heat stress with dry bulb temperatures of 44 C 

 for 4 hours or more, the animals showed no apparent failure to 

 maintain the thermal equilibrium (Fig. 4). Temperatures of periph- 

 eral parts like the feet and tail, rose rapidly to levels almost 



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