CHAPTER XV 



Marsupialia 



In our collection, the marsupials are represented, un- 

 fortunately, by but a few specimens; though this Deseado 

 fauna included, as is shown by the fragmentary remains, 

 a wide range of forms from Pilchenia, the size of a mouse, 

 up to the bear-sized Proborhyaena. The small forms were 

 probably insectivorous, while the larger forms took the 

 place of the carnivors, the absence of true Carnivora being 

 one of the striking features of the fauna of South America 

 during earlier Tertiary times. 



The treatment of these forms has been as varied as their 

 sizes. Ameghino, with his idea that the Casamayor and 

 Deseado beds were Cretaceous in age, groups the larger 

 forms as a suborder, Sparassodonta, and considers them 

 ancestral to the Creodonta; while the small forms make up 

 his Sarcobora which he considered ancestral on one side to 

 the rodents, on the other to the diprotodont marsupials. 

 Sinclair, after showing the marked similarity of the Spar- 

 assodonta to the polyprotodont marsupials, especially the 

 genus Thylacyniis, abandons that term and puts them in 

 the family Thylacynidae along with the Australian forms; 

 the Microbiotheridae he finds similar to opossums and 

 puts in the family Didelphidae; while the remaining small 

 diprotodont forms he associates with Cacnolestcs, and using 

 Ameghino's families as subfamilies makes three divisions 

 of the family, Palaeothentinae, Garzoninae, and Abderitinae. 

 Matthew finds the sparassodonts to be true marsupials, 

 and without phylogenetic relationship with the creodonts. 

 Gregory diagrams the sparassodonts as coming from gener- 

 alized didelphids and derives them from the same line as 

 the Australian polyprotodonts; while the small caenoles- 



