THE EOCENE OF EUROPE AND NORTH AMERICA 



Ot 



West Indies and New South Wales. The sequoias are represented by 

 Nordenskioldia. Among the northern trees are willows, oaks, and planer 

 trees (Planera). 



III. MIDDLE AND UPPER EOCENE LIFE OF EUROPE AND 



AMERICA 



Near the close of the Lower Eocene the interchanges of mammalian life 

 between the New and Old Worlds apparently ceased, and the mammals 

 of the two great holarctic colonies entered upon a long period of independent 

 and partly divergent evolution which lasted until the summit of the Eocene, 



MIDDLE EOCEINE: 



Fig. 46. — Middle Eocene. A period of continental depression, or geographic isolation of 

 the New and Old World mammals, resulting in prolonged independent evolution and adaptive 

 radiation on the great continents. Australia probably separated. The archaic and modern 

 mammals giving rise to independent groups of mammals in (1) North America, (2) Eurasia, 

 (3) North Africa, (4) South America. Rearranged after W. D. Matthew, 1908. 



as first pointed out by the Avriter in 1899 ^ and subsequently emphasized by 

 Stehlin - and Matthew.^ Whereas in the Lower Eocene, owing to a contin- 

 uance of the Basal Eocene community of life and to the invasion of similar 

 modernized families, the two continents, that is, western Europe and the 

 Rocky Mountain region, were united by the presence of nine families and 



' Osborn, H. F., Tertiary Mammal Horizons of Europe and America, 1899-1900, p. 7 fol- 

 * Stehlin, H. G., Sur Ics Mammif^res des Sables Bartoniens du Castrais. Bull. Soc. Geol. 



France, Ser. 4, Vol. IV, May, 1904, p. 47-3. 



■■'Matthew, W. D., Hypothetical Outlines of the Continents in Tertiary Times (p. 361). 



Bull. Amer. Mua. Nat. Hist., Vol. XXII, Art. xxi, Oct., 1906. 



