EDENTATA OF THE SANTA CRUZ BEDS. 361 



RELATIONSHIPS OF THE EDENTATA. 



It must be admitted that the Santa Cruz fossils throw but little light 

 upon the very obscure and difficult problems concerning the origin of the 

 Edentata and their relations to other mammalian groups. Such light can 

 be obtained only from a fauna of much more considerable geological 

 antiquity, though, if the exceedingly curious animals, which Ameghino 

 has described as Adiastalttis and Anathitus and referred to the Monotre- 

 mata, were better known, they might afford a valuable clue to the solution 

 of the mystery. So far as it goes, the evidence of the Santa Cruz fauna 

 is not in favor of Wortman's most interesting hypothesis ('96, '97) that 

 the Edentata were derived from the Ganodonta. This hypothesis rests 

 chiefly upon a series of resemblances between the latter group and the 

 Pleistocene genus Mega/onyx, and more especially upon the identification 

 of the first tooth in each jaw of the Gravigrada as a canine. Even in 

 regard to the upper tooth this identification is exceedingly doubtful, and 

 there is much more reason to consider the tooth a premolar. In the case 

 of the lower tooth, however, the determination is clear, for this tooth, 

 almost without exception, bites behind the upper caniniform and therefore 

 cannot itself be a true canine. More important is the fact that the Santa 

 Cruz Gravigrada are less like the Ganodonta than are the Pleistocene 

 genera, which of course would not be the case if the Ganodonta were the 

 true ancestral group ; we should then find that the farther back the eden- 

 tate line were traced, the more closely it would approximate the ganodonts. 

 Wortman too is quite mistaken in supposing that the earliest appearance 

 of the edentates in South America "does not antedate the Santa Cruz 

 epoch" ('97, 104). On the contrary, they occur in the oldest known 

 Tertiary, and possibly even pre-Tertiary, deposits of Patagonia, and there 

 is every appearance of their having been indigenous in that region. It 

 cannot be pretended that the evidence of the Santa Cruz fauna definitely 

 disproves Wortman's hypothesis, but it does render it distinctly less prob- 

 able. On the other hand, Osborn's recent discovery of a true armadillo 

 in the Bridger Eocene of North America ('04), removes the formidable 

 geographical difficulty which had formerly attended that hypothesis. 



Although the Santa Cruz fauna thus gives us little help in determining 

 the relationships of the Edentata to other mammalian orders, it affords 

 abundant testimony to the unity of origin of the American edentates. 



