EVOLUTIONABY ASPECTS IN MAMMALS 



armadillos in Kansas, spreading rapidly northward. At present the 

 animal is still spreading north and east in the United States, Accord- 

 ing to Talmage and Buchanan (1954), the migration of the armadillo 

 is one of the most amazing in the animal kingdom, comparable 

 almost to the lemming migrations. From the distribution area it is 

 apparent that the armadillo faces very diversified ecological situa- 

 tions and that its success must at least partly be dependent upon 

 an extraordinary ecological potential, while the other members of 

 the order, the sloths and an teaters, are still confined to their tropi- 

 cal habitat. The entire range of the armadillo is characterized by 

 having neither extreme cold nor extended periods of cold weather. 

 The northern parts of the area, however, occasionally show quite 

 low temperatures for short periods and have atypical seasonal and 

 diurnal periodicity. This unique dispersion rate, bringing the animal 

 out of the tropical stability and into the periodicity of seasons and 

 larger diurnal variations, plus its phylogenetic position, suggested 

 to me that some valuable information in regard to the phylogenetic 

 development of homeothermy could be expected. 



The diurnal cycle of deep rectal temperature under controlled 

 conditions is presented in Figure 9 . At a constant air temperature 

 of 25 C, the diurnal cycle ranges between 34.0 C and 36.4 C. 

 The animals were free to build nests from dry hay and were con- 

 fined in a room of considerable size allowing for exercise. The 

 diurnal cycle is obviously related to their nocturnal activity pattern. 

 Following forced exercise, the deep body temperature may increase 

 to 37 G or 38 G. At 30 G ambient temperature the animals were 

 usually very sedate, no signs of discomfort, and rectal and skin 

 temperatures were nearly constant, the difference between the two 

 being surprisingly small. A rectal temperature of 34.5 C could 

 correspond to a skin temperature on the soft belly as high as 34.2 C 

 and on the armor 33.9 G. Under these conditions the gradient is 

 less than 1 G between the core and the shell. The oxygen uptake 

 showed only small variations and ranged from 200 cc to 275 cc of 

 oxygen per kilo animal per hour. Figures 10 and 11 demonstrate 

 these points; a slight lowering of the air temperature brought about 

 a dramatic response. The most conspicuous feature was a sudden 



increase in rectal temperature. Thus, if the air temperature was 



o o 



decreased from 30 G to 25 C, the deep rectal temperature might 



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