VARIOUS INVASIONS 25 



merit which arose in situ. The reasons for the affinities 

 expressed in the different groups will be found in the intro- 

 ductory paragraphs of the systematic discussion of each 

 group. 



The Notungulata, including the Typotheria, the Toxo- 

 dontia, the Litopterna, the Homalodontotheria, and the 

 Astrapotheria are a group with apparently a common an- 

 cestry. In Patagonia they have specialized into the various 

 subdivisions as we find them in the Deseado. This group 

 was in Patagonia as early or earlier than the Casamayor. 

 Their relationships appear to me to be with the Hyracoidea 

 which are generally credited with originating in Africa. 



The Pyrotheria are related to the early elephants which 

 also arose in Africa, but it seems to me that this form 

 came to Patagonia at least at a later period, making its 

 first appearance in the upper part of the Astraponotus 

 period. Ultimately the elephants and Hyracoidea had a 

 common origin in Africa. 



The Rodent ia are all hystricomorphs and appear in 

 South America for the first time in the Deseado. They 

 also occur in the Oligocene of Europe and the Fayum of 

 north Africa. They never reached Xorth America so must 

 have come to South America by some southern route. 



The Edentata are an element of the Casamayor fauna 

 and as there is no evidence of their originating anywhere 

 else it would seem that they were indigenous to South 

 America, where they later flourished and developed the 

 greatest variety and profusion of numbers. 



The group of marsupials is an element the origin of which 

 presents a most difficult problem. Some belong to the 

 oppossum series which could well have been developed 

 from some remnant of the Mesozoic marsupial fauna that 

 had a world wide distribution; but the presence of dipro- 

 todonts, which are characteristic of Australia, and of the 

 Borhyaenidae which are closely related to the Thylacinidae 

 of Australia, suggests a migration from that continent as 



