616 LAND MAMMALS IN THE WESTERN HEMISPHERE 



high processes for the support of the carapace, just as in the 

 Recent genera. The Umb-bones did not differ in any signifi- 

 cant way from those of the latter, and the feet closely resembled 

 those of the modern Dasypus; none of the genera displayed the 

 specialization of the manus seen in Cdbassous, Priodontes or 

 Tolypeutes. Whether these specializations have all been 

 acquired since Santa Cruz times, or whether they had already 

 appeared in some other region of the continent, is a question 

 that remains to be determined. 



Little can yet be done in the way of tracing the history of 

 the armadillos through the stages preceding the Santa Cruz 

 times, because of the fragmentary character of the material. 

 The suborder was abundantly represented in the Deseado 

 stage, in which some of the Santa Cruz genera existed. Even 

 in the most ancient of the Patagonian Tertiary formations are 

 found scutes of the carapace essentially like those of the modern 

 armadillos. The group is thus of very high antiquity, older 

 than any other of the suborders is known to be. 



In addition to the typical armadillos of South America, 

 there were, in other continents, certain more or less doubtful 

 forms, concerning which a word should be said. In the Bridger 

 Eocene of North America was a genus {'fMetacheiromys) of 

 armadillo-like animals, the true relationships of which are far 

 from clear. The teeth were mostly lost, leaving but one on 

 each side of each jaw, and this was covered with enamel, which 

 is not true of any unquestioned edentate. However, this is 

 not an insuperable objection to the inclusion of these animals 

 in the edentates, for there can be no doubt that these were 

 derived from ancestors with enamel-covered teeth. Even in 

 modern armadillos the enamel-organ is formed in the embryo, 

 though it does not perform its functions. The skull of fikfeto- 

 cheiromys had something of the armadillo-shape, but was not 

 especially characteristic. The vertebrae of the neck were all 

 separate, and those of the dorsal and lumbar regions did not 

 have the complex articulations common to all known edentates. 



