362 PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



The so-called edentates of the Old World have very little in common 

 with the American orders and probably are not related to them. At all 

 events, the Santa Cruz fossils do not even tend to bridge the gap between 

 the two series. 



As was pointed out in a previous section (this volume, p. 4), there is 

 strong reason to believe that all of the edentate orders had come into 

 existence as such before Santa Cruz times, although no representatives 

 of the ant-eaters or of the true sloths (Tardigrada) have yet been found 

 in the Santa Cruz or older formations. It is doubtless true of those two 

 orders, as it is of the three others, Dasypoda, Glyptodontia and Gravi- 

 grada, which are well represented in the Miocene fauna, that at that time 

 the various subdivisions of the edentates had not yet become so widely 

 separated by divergent evolution as they afterwards were. In other words, 

 as we trace these groups backward in time, we find them converging 

 more and more closely to a common term, and this is a highly significant 

 fact, as indicating their monophyletic origin from a single ancestral group. 



It further appears probable that the five orders, or suborders, of the 

 Edentata did not arise simultaneously from the hypothetical ancestral 

 group, but that the first division was into two principal branches. One 

 of these branches subsequently gave off the armadillos and glyptodonts, 

 while the other divided into the ground sloths, ant-eaters and true sloths. 

 This conclusion is indicated by a comparison of the Santa Cruz arma- 

 dillos and glyptodonts, on the one hand, with those of the Pampean, on 

 the other, which shows not only that these two orders were much nearer 

 together in the former epoch than in the latter, but also that they were 

 more like each other than either is like any other order of edentates. 

 This resemblance is by no means confined to the presence of a dermal 

 armor in both groups, but extends to nearly all parts of the skeleton 

 and even, in some small degree, to the dentition, and justifies the inclu- 

 sion of both orders in the higher group Loricata. 



It would be very interesting to learn whether the earliest edentates 

 possessed dermal ossifications. That such was the case, is rendered to a 

 certain extent probable by the presence of these ossifications in the Pleis- 

 tocene Mylodontidce. On the other hand, no trace of armor has been 

 found in association with any of the Santa Cruz Gravigrada, though the 

 extremely scanty and imperfect remains of the Mylodontida in the beds 

 of that epoch deprives this fact of importance, so far as that particular 



