THE PLIOCENE OF EUROPE, ASIA, AND NORTH AMERICA 339 



Reunion with South America. — As the Pliocene was an epoch of eleva- 

 tion of all the continents, it affected eastern North America after some 

 oscillations, but before the termination of the marine Pliocene the per- 

 manent connection of the peninsula of Florida with the North American 

 continent was accomplished/ 



After an interval of separation which, so far as the mammal record 

 goes, extended back to the Upper Cretaceous or Basal Eocene, South 

 America became again united with North America, and an interchange of 

 mammals took place; some physical, climatic, or biotic barriers were un- 

 doubtedly removed. The previous separation need not have been at 

 Panama, as is generally assumed -' ; Hill •' believes that from the close of 

 the Oligocene onward the waters of the Atlantic and Pacific have been 

 separated at this point; in other words, that the Isthmus of Panama is as 

 old as the Oligocene. Ortmann ■* has suggested the adoption of von Iher- 

 ing's hy])othesis ' that the water barrier existed for a long period across 

 the parallel of the present Amazon River. 



The supposed discovery of the remains of large sloth-like or gravigrade 

 edentates in the Middle Miocene (Mascall) of Oregon and in the Lower 

 Pliocene (Alachua Clays) of Florida makes it appear possible that these 

 mammals were resident in North America throughout the Age of Mammals, 

 but tliis does not remove the significance of the great invasion of these 

 animals from South America in Lower and Middle Pliocene times. In 

 this connection Scharff's hypothesis" should be considered. (Compare 

 p. 93.) 



Evidence of fish faunas. — As regards the theory of a long prevailing 

 separation of North and South America in Ciienozoic times, the freshwater 

 fishes, on the whole, supplement the evidence afforded by the mammals. 

 Eigenmann ^ (1906) makes the statement that North America has not 

 contributed a single element to the freshwater fish fauna of South America. 

 This, however, should be compared with the statement on p. L36. The 

 l^eginnings of intercommunication are shown by the fact that two promi- 

 nent South American families, the Characinidie and Cichlidae, have at the 

 present time representatives as far north as the Rio Grande River, while 



' Dall, W. H., Geological Results of the Study of the Tertiary Fauna of Florida. Trans. 

 Wagner Inst., Vol. Ill, Pt. 6, 1903, p. 1.5.50. 



^ Matthew, W. D., Hypothetical Outlines of the Continents in Tertiary Times. Bull. 

 Amer. Mus. Nat. Hist, Vol. XXII, Art. xxi, 1906, p. -36.5. 



^ Hill, R. T., Geological History of the Isthmus of Panama and Portions of Costa Rica. 

 Bull. Mus. Comp. ZooL, Vol. XXVIII, 1908, p. 270. 



* Ortmann, A. E., Von Ihering's Archiplata-Archelemis Theory. Science, n.s.. Vol. XII, 

 no. .311, Dec. 14, 1900, p. 929. 



^ Von Ihcring, H., The History of the Neotropical Region. Science, n.s.. Vol. XII, 

 no. 310, Dec. 7, 1900, pp. 8.57-864. 



• Scharff, R. F., On an Early Tertiary Land-Connection between North and South America. 

 Amer. Natural., Vol. XLIII, Sept., 1909, pp. 51.3-531. 



. " Eigenmann, C. H., The Fresh-water Fishes of South and Middle America. Pop. Sci. 

 Month., June, 1906, pp. 515-530. 



