152 ORIGIN OF LIFE IN AMERICA 



support its being one of the dog tribe (Canidae), we should 

 hesitate before accepting the earlier opinion. 



The genus Procyon, to which the North American raccoon 

 belongs, only makes its appearance in the Pleistocene Period. 

 Nevertheless, it is quite possible that cave deposits, such as 

 that described from McCloud River in California containing 

 the new species Procyon sinus, may eventually be placed in 

 the Pliocene series.* At any rate, the genus Procyon must 

 have existed before Pliocene times, and it seems to me prob- 

 able that it originated either in South America or in some 

 western lands which have long since subsided. Dr. von 

 Ihering f believes that the Procyonidae have undoubtedly 

 come from eastern Asia. Why he should think so I cannot 

 imagine, for neither recent nor fossil species are known from 

 that continent. 



It is now generally admitted, as I mentioned already 

 (p. 95), that Central America assumed its present shape and 

 contours at some time during the Pliocene Period (compare 

 p. 243). As soon as this land bridge became habitable for 

 terrestrial animals, northern species are supposed to have 

 poured across it into South America. We possess strong 

 evidence certainly that a steady stream of southern animals 

 invaded the northern continent in Pliocene and even in 

 Pleistocene times and that northern ones succeeded in reach- 

 ing the south. 



The group of the so-called toothless mammals (Edentata), 

 comprising the ant-eaters, sloths and armadillos, are almost 

 entirely confined to South America; and that continent no 

 doubt is their original home. A few penetrated in some 

 mysterious manner to North America in Eocene times, as I 

 shall explain more fully in another chapter. Shortly after- 

 wards they seem to have become extinct again in North 

 America, for no traces of edentates have yet been discovered 

 in the succeeding Oligocene deposits. It is only in the 

 Miocene beds of North America that we again meet with 

 examples of this curious group. They were representatives 

 of the huge Megalonyx which is closely allied to a southern 



* Gidley, J. W., " Fossil Eaccoon from Calif ornian Cave." 

 t Ihering, H. von, " Siidamerik. Raubtiere," p. 160. 



