JOHANSEN 



entirely lacks the potential to shiver. The three-toed sloth seems 

 in his unique laziness to depend upon his exceptionally high insula- 

 tion — nearly as great as that of many arctic animals. The result 

 is an extremely labile body temperature which at low air tempera- 

 tures shows greater fluctuations than encountered even in the mono- 

 tremes. The three-toed sloth seems to be the least fitted of all mam- 

 mals to withstand decreased air temperatures, a fact which I think 

 illustrates the importance of metabolic compensation for mainten- 

 ance of thermal balance. The other members of the Xenarthra show 

 a far more advanced temperature regulation. The armadillos are 

 very versatile animals with large distribution areas, as explicit in 

 their temperature- regulating capacity. More or less casual observa- 

 tions of body temperature of armadillos were made and reported 

 by de Almeida and de A.Fialho (1924). Eisentraut (1932) recorded 

 an average body temperature in Tolypeutes conurus of 32 C in a 

 tropical habitat. Wislocki (1933), studying the nine-banded armadillo 

 in Panama, reported 34.5 C as an average body temperature at air 

 temperatures around 25 G.I have recently done a study on tem- 

 perature regulation in this same species and will submit some of 

 these data in a little more detail. 



The material studied came from Texas and not from tropical 

 Central America where most of the earlier observations on this 

 species have been made. I mentioned earlier that the dispersion 

 of animal life north and south from the tropics is a factor presum- 

 ably of great importance in the evolvement of more refined homeo- 

 thermic adjustments. It struck me that the nine-banded armadillo 

 is one of very few animals that incur time has taken steps to leave 

 the tropical stability. The distribution area for the nine-banded 

 armadillo is today very large. It ranges south into Northern 

 Argentina, spreads over all of the countries east of the Andes, 

 reaches the Pacific Coast in Ecuador, and extends throughout 

 Central America and most of Mexico. About a hundred years ago, 

 the animal crossed the border into the United States and is now well 

 established in most of Texas, the southern part of Arkansas and 

 Oklahoma, most of Louisiana, and southwestern Mississippi. Fur- 

 thermore, it is established in Alabama and Florida. In Florida, 

 the armadillo is reported to have increased its range by about 50% 

 from 1954 to 1958. There are also persistent reports that there are 



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