3o6 



CHAPTER III 



more abundant material available reveals the presence of brachypterous individuals 

 in Alaska. 



The following reconstruction of the history of Bembidion transparens in North 

 America is the most plausible:— Immigration from northeastern Asia in early 

 Pleistocene and subsequent spread to the Atlantic coast. Interruption of area 

 during one or more glacial periods in the western and central parts. Survival, at 

 least throughout the last glaciation (Wisconsin), in the Northeast. Postglacial re- 

 colonization of lost area from the east, possibly also from the west. 



The distribution in Newfoundland (fig. 59) suggests glacial refuges on the coast, 

 in the northwestern, northeastern and southeastern parts. —A similar coastal refuge 

 during the last glaciation was assumed for this species in northeastern Fennoscandia 

 (Lindroth, 1949, p. 389 a.f., fig. 45). 



The fossil evidence 



The importance of reliably dated fossils to the reconstruction of faunal and floral 

 history is immense. Our knowledge of what actually happened, and thus the 

 interpretation of the present pattern of distribution, has often been radically 

 altered by the discovery of a single fossil specimen. 



The difficulties lie in a competent identification of the often fragmentary re- 

 mains, but also in the scope of conclusions. Above all, considering what a futile 

 fraction of organisms existing during a certain geological period was by chance 

 fossilified, and how still more futile a fraction of them was discovered and came to 

 the notice of a specialist, it is extremely dangerous to conclude anything from 

 negative facts, from the seeming lack of a certain type of animal, in a certain area, 

 from a certain period. 



Yet fossils may show that many gaps in the present area of an animal group or 

 species are secondary and that faunal connections once existed which are impossible 

 to reconstruct from the recent distribution. 



This applies very much to the question of faunal exchange between Europe 

 and North America. The fossil faunas of both of these continents are the best 

 known in the world and, partly— at least — for this reason, many fossil forms were 

 regarded as Eur-American or a group of animals or plants now restricted to either 

 continent was discovered as fossil in the other. 



The resemblance of these faunas was apparently greater in remote times and 

 this, as described above (p. 286), originally led Simpson to conclude, mainly from 

 fossil Mammalia, that a broad transatlantic connection existed in the Lower 

 Eocene; later he found this assumption unnecessary. It is worth mentioning in 

 this connection that the insect fauna described by Henriksen (1922) from Lower 



