INTRODUCTION 



67 



an extensive continent united northern Europe and Arctic North America. 

 The southern shores of this continent extended from the British Isles to 

 NewfoumUaud in a ii,nnit curve. He points out that the fossil flora proves 

 that the subsidences of the northern Atlantic which separated Eurojjc and 

 America were geologically recent, that is, of late Pliocene and Pleistocene 

 times. So few remains of fossil mammals have been found on the eastern 

 coast of North America that the hypothesis of Scharfi" of a broad North 



17. — Chief centers of the adaptive radiation of the orders of mammals so far as 

 known at the present time. 



Atlantic land connection during a considerable part of the Age of Mammals 

 is neither supported nor disproved by such negative evidence. 



Other authors '■ believe that the connections and migration routes be- 

 tween Europe and North America were chiefly North Pacific or via Asia and 

 the region of Behring Straits. 



Even if the north polar center theory of Haacke be extreme and the 

 evidence for a north Atlantic land mass is less strong than that for North 

 Pacific land connection between the New and Old worlds, the fact remains 

 undisputed somewhat in the form stated by Wortman, that the northern 

 portions of Europe, Asia, and North America formed the greatest creative 

 center, proba})ly during the Age of Reptiles and certainly during the Age 

 of Mammals. Striking evidence for this is found in the great number and 

 variety of the orders of mammals which have been discovered early in Eocene 

 and Lower Oligocene times in Europe and North America, which with Asia 

 constitute the region Holarctica. 



These orders of mammals (compare p. 73) are as follows: 



* See Matthew, W. D., Hypothetical Outlines of the Continents in Tertiary Times. 

 Bull. Amer. Mas. Nat. Hist., Vol. XXII, Art. XXI, Oct. 25, 1906. 



