HASEMAN, GEOGRAPHICAL DISTRIB UTION IN SO TJTH AMERICA 99 



polyprotodont or carnivorous forms, allied to the existing Tasmanian 

 wolf [Thylacynus) and of the small diprodont herbivorous forms (Cceno- 

 lestes) very remotely allied to the phalangers and other Australian 

 diprotodonts. 



The researches of Broom, Gregory, Dieder and others seem to favor 

 the view that Ccenolestes is an independent offshoot of the polyprotodont 

 type which was present in the Eocene of North America and the Oligo- 

 cene of North America and Europe. It is also to be noted that the 

 Patagonian csenolestoids (Epanorthus and its allies) show no clear evi- 

 dence of dose relationship with Australian diprotodonts. 



There can be no doubt that the sparassodonts are true polyprotodont 

 marsupials, as shown by Sinclair. They also agree with the Tasmanian 

 Thylacynus in certain characters which have been assumed to indicate 

 that they belong to the same family. Dr. Matthew, however, is now of 

 the opinion that these few characters have probably arisen independently 

 in the Patagonian and Tasmanian genera by virtue of parallel evolution 

 from primitive didelphids of northern origin. 



The Tasmanian and Patagonian genera are the end result of cenotelic 

 evolution. It was not these genera which were widely distributed, be- 

 cause there are none in common. It was their ancestral stock, if they 

 are genetically related, which became widely distributed, 



In the case of the cichlid fishes, I have shown that it was not any of 

 the living genera which were distributed into Africa and South America, 

 but it was a primitive form. Could not this ancestral marsupial, from 

 which Thylacynus on one hand and the sparassodonts (Borhycena, etc.) 

 on the other evolved, have originated in the northern hemisphere from 

 some primitive northern polyprotodont during the Mesozoic to -early 

 Eocene? At any rate, it is not yet known from either Patagonia or 

 Tasmania. 



This primitive ancestor could have been pushed out of Asia into Aus- 

 tralia and out of North America during the late Cretaceous to early 

 Eocene into South America. Then similar evolution in similar environ- 

 ments would easily account for the rest of the similarity of the Pata- 

 gonian and Tasmanian Thylacynidse. 



Until it has been definitely shown what this primitive ancestor of the 

 Thylacynidse was and where it originated, it appears to be useless to 

 reconstruct the surface of the earth from such evidence. 



It is interesting to note that the evolution of the South American 

 mammals agrees in a general way with Schuchert's view of the connec- 

 tions which have existed between North and South America. The first 

 connection existed from the late Cretaceous to the early Eocene, and then 



