900 



SCIENCE. 



[N. S. Vol. XVII. No. 440. 



TEE EDENTATA OF TEE SANTA CRUZ 

 BEDS.* 



In the Santa Cruz fauna tlie edentates 

 form one of the most conspicuous elements, 

 both in the abundance of individuals and 

 in the number and variety of the genera 

 and species. As a whole, they are strik- 

 ingly different from those of recent times, 

 for of the three orders virhich are repre- 

 sented among the fossils, armadillos, glyp- 

 tedonts and ground-sloths, only the first- 

 named persists to the present day, the 

 other two being extinct. On the other 

 hand, no trace has yet been found in the 

 Santa Cruz beds of the true sloths or of 

 the anteaters. It can hardly be doubted 

 that both of these orders had already be- 

 come differentiated and were in existence 

 as such. If so, however, they must have 

 originated in some other part of the South 

 American continent, and were prevented 

 by climatic or other barriers from extend- 

 ing their range into Patagonia. One fact 

 which clearly justifies this assumption is 

 the relatively small degree of structural 

 change that took place between the eden- 

 tates of the Santa Cruz and those of later 

 periods, such as the Pampean. There are 

 many differences of detail between the 

 earlier and the later forms, but nothing 

 comparable to what would be implied in 

 the derivation of the sloths or anteaters 

 from any known Santa Cruz fossils. 



As will be shown more at length in a 

 later section, much the same statement ap- 

 plies to the armadillos of the Santa Cruz 

 beds, Avith reference to their connection 

 with those of modern times. Speaking 

 broadly, the latter would appear not to 

 have been derived from the former, which 

 suggests that Miocene Patagonia was 

 rather an outpost of the South American 



* From the forthcoming Vol. V. of the ' Reports 

 of the Princeton University Expeditions to Pata- 

 gonia.' 



fauna than the main area of its develop- 

 ment. 



The Santa Cruz glyptodonts are, on the 

 whole, markedly more primitive than those 

 of the Pampean, and in many structural 

 details show a closer connection with the 

 armadillos than do the latter; but for the 

 most part, the Santa Cruz genera do not 

 appear to be directly ancestral to those of 

 the Pampean. Like the armadillos, they 

 seem to be aside from the main lines of 

 descent which terminated in the giant 

 types of the Pleistocene. 



On the other hand, the Gravigrada ap- 

 pear to be more directly ancestral to the 

 great Pampean forms, and representatives, 

 if not the actual ancestors, of almost all 

 the genera may be observed in this fauna. 

 However, no entirely convincing solution 

 of these problems can be obtained until 

 the fossils intermediate in time between 

 the Santa Cruz and the Pampean are more 

 fully known. 



A remarkable feature of the Santa Cruz 

 edentates is their variability within certain 

 well-defined limits. As a rule, the genera 

 may be readily identified, but the species, 

 especially of the Glyptodontia and Gravi- 

 grada, present extraordinary difficulties to 

 the systematist. This variability, how- 

 ever, confines itself to comparatively unim- 

 portant details, and the characteristics of 

 the three orders and of the families and 

 genera within those orders are already, for 

 the most part, firmly established, though 

 transitional forms from species to species 

 and, less commonly, from genus to genus 

 abound. 



1. The Santa Cruz edentates are rela- 

 tively small animals and a few of them 

 are really minute. As compared with the 

 ground-sloths and glyptodonts of the Pam- 

 pean, they are pygmies, but the armadillos 

 have a greater number of large species 

 than exist at present, though none of them 



