MATTHEW, CLIMATE AND EVOLUTION ]!(1» 



they are associated is in part closely related to the Paleocene fauna of 

 Europe and jSTorth America and for this reason has been regarded as 

 equivalent. But these genera of Northern affinities are associated with 

 a large number of larger and more progressive genera, structurally de- 

 rivable, according to the canons of evolutionary development universally 

 accepted by paleontologists, from the more primitive types which are 

 common to the Notostylops beds and the Paleocene of the North, and 

 leading apparently into the various specialized groups peculiar to the 

 later South American Tertiaries. These more progressive types are un- 

 known to any northern Tertiary fauna; they appear to be derived from 

 the more primitive group whose affinities are so close to the Puerco, 

 Torrejon and Cernaysian mammals; and they point to the conclusion 

 that the Noiostylops fauna is in reality decidedly later than the Paleo- 

 cene, the more primitive group of its fauna being little altered survivals,^^ 

 corresponding to the primitive survivals (Condylarthra, etc.) which are 

 found in the Wasatch and Wind Eiver faunse of North America. Taking 

 the Notostylops fauna as a whole, it appears to me to represent an Eocene 

 stage of development, conditioned by an isolation which began in the 

 Paleocene and hence prevented the incoming of any Perissodactyla, 

 Artiodactyla or Carnivora from North America.^" This same isolation 

 will satisfactorily account for a later survival of the dinosaurs, of Meso- 

 zoic Crocodilia and some other primitive elements, if they Avere in fact 

 contemporary with the Notostylops fauna. 



The age of the Pyrotherium beds is much less definitely determinable. 

 Dr. Roth, indeed, doubts the existence of this faima as distinct. If 

 accepted, it would presumably be intermediate between the Notostylops 

 and Santa Cruz faunae and provisionally referable to the Oligocene. 



The sequence of the Argentine faunae will then be 



Pampean (s. s.) = Pleistoceue 



Monte Hermoso etc. =: Pliocene 



Santa Cruz z= Miocene 



Pyrotherium = ? Oligocene 



Notostylops = P>ocene. 



So far as the correlation of the Pampean and Santa Cruz is concerned, 

 their fossils agree wholly in preservation and degree of petrifaction with 

 those preserved in similar Pleistocene and late Miocene formations, re- 



^ Little altered, that is to say, so far as the parts known to us are concerned : their 

 adaptation, whatever it was. not involvinsr radical changes in dentition from the primary 

 type. 



-^ Schlosser Mn Zittel's Grundziige d. Pal.. Rev. Ed. 1912) regards the Notostylops 

 fauna as T'pper Eocene. Scott (History of Mammals of West. Hem.) places it as Eocene. 



