VARIOUS INVASIONS 25 
ment 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 7Typotheria, 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 //yracoidea 
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 Rodentia 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 North 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 
