CHAPTER IX 

 THE EDENTATES 



RETROGRESSION IN EVOLUTION 



Origin and peculiarities of the Edentata — Relation of loss of 

 teeth to sknll form — Extinct Armadillos — The zygoma — 

 Experimental results of loss of teeth- — Interpretation of 

 changes in the human sknll — Old-World Edentates. 



The animals included within the order Edentata are un- 

 doubtedly modern representatives of stocks differentiating in 

 very remote times from general mammalian ancestors. It is 

 doubtful if all belong in reality to a single order; indeed it is 

 becoming usual to subdivide them in the following manner: 

 the African Aard-varks as possibly related to the very early and 

 primitive Ungulates ; the Oriental Pangolins of unknown an- 

 cestry; and the American Edentates, the Sloths, Armadillos, 

 and Anteaters, now widely divergent in superficial features but 

 without doubt of common derivation. 



The name of the order is itself particularly unfortunate 

 since only the Anteaters and Pangolins are entirely toothless 

 and even in the jaws of these animals vestiges of tooth bands 

 have been discovered. Nevertheless, all members of the order 

 lack median incisors and in this restricted sense they are en- 

 titled to the term Edentata. 



As regards milk dentition no indication has yet been dis- 

 covered in the Sloths. On the other hand, temporary teeth 

 have been found in the Aard-vark and in the Armadillos. 



In general it may be said that although the teeth of the 

 Edentates vary in number from-^ in the Sloths to as many as 

 100 in one of the Armadillos they always present certain gen- 



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