198 ANNALS iVBW YORK ACADEMY OF SCIENCES 



ing via North America would compel Amcghino to conclude tliat tlieir 

 first occurrence in South America in these same sub-Pampean beds must 

 be materially later than the evolution of the phylum in the Pahearctic 

 region (Miocene) and that the genus Arctotherium of the true Pampean 

 ill South America, unknown in North America until the Pleistocene, 

 inilicates, like Equiis, that the Pampean is ft Pleistocene formation. 



The distribution of Smilodon in North and South America is in exact 

 accord with that of Arctotheriuin. Tlie relations of the South American 

 Proboscidea to those of North America correspond to those of the Equidse. 

 The Camoliflffi, Cervidse, Canidjp, etc., also snpport the Pleistocene age 

 of the true Pampean. The Edentata, whose migration appears to have 

 been in the reverse direction, will be discussed later. 



In the Santa Cruz fauna, we have not the direct evidence that the 

 Pampean faunse afford for correlation by means of groups of admittedly 

 northern origin. The evidence has been very fully discussed by Hatcher, 

 Ortmann, Scott and others, and so far as it is based upon the relations 

 and age of associated marine formations, I am not competent to criticize 

 it. The criterion used by Ameghino and Roth, of proportions of extinct 

 to living genera, I regard as untrustworthy, partly for the general reasons 

 already given (p. 192) and partly because of the personal equation that 

 must always affect the number of genera and species described as new, 

 as compared with those referred to known genera and species. Unless 

 the standards of diversity for genera and species were approximately the 

 same, and in this instance they are certainly very wide apart,-® the com- 

 parison of the proportions of extinct to surviving genera and species in 

 Argentine formations with those of Europe or North America would be 

 misleading. 



Perhaps the most important correlation is that of the Notostylops 

 fauna. Lower Cretaceous according to Ameghino, Upper Cretaceous ac- 

 cording to Roth, Paleocene according to Gaudry, Upper Eocene in Schlos- 

 ser's view. Here there is an apparently strong point for Cretaceous 

 age in the presence of dinosaurs in association with the fossil mam- 

 mals. Dinosaurs disappeared from the Northern world at the end of 

 the Cretaceous.^^ They are entirely unknown in any Tertiary formation. 

 Nevertheless, the possibility of their survival into the early Tertiary in 

 South America must be considered.^® The mammalian fauna with which 



=' The European fossil rodpnts are. for tlie most part, roferrei in accordance with the 

 (lid conservative standards of senera and species, while Ameghino Is much inclined to 

 hairsplitting in generic and specific distinctions. Scott In his revision Is more conserva- 

 tive, but not so as to equalize the standards in question. 



" The latest dinosaur formations of North America are. however, regarded as Paleo- 

 cene by Knowlton, Lee. Pealo and other authorities. 



28 The same arguments apply to the occurrence of a Mesozolc type of Crocodile, 

 .\ Dfiisiii-liiiH, in the \otof!t!il<)i)s fauna. 



