The relationship between the palaearctic and nearctic faunas 



307 



(From Traite de Zool.) 



(From Ander, 1942.) 



FIG. 60. Distribution of the beetle family Cupedidae, recent and (in Europe) in Baltic 

 amber. The figured specimen is of Cupes rajjrayi Fairm. from Madagascar. 



Eocene Diatom-earth in Denmark has its closest geographical connection with 

 Southern Asia. 



Now, the distribution of existing species, and usually even of genera, is little 

 affected by what happened in the early Tertiary. The first period in which possibly 

 still existing species had developed within the terrestrial fauna was the time of the 

 Baltic amber, usually referred to Upper Eocene (or Lower Oligocene), that is 

 more than 40 million years ago. It happens that one of the most famous insect 

 specimens of the amber, a Tiger-beetle of genus Tetracha (Megacephala), has a 

 special bearing upon our problem. It is often regarded as the single instance of an 

 insect species still living unchanged since that time (Ander, 1942, p. 26)^, since W. 

 Horn (1906), though with some doubt, declared it as identical with the American 

 T. Carolina L., distributed from Virginia through Central America to northern 

 Chile. The genus has a wider occurrence (S Spain, Africa, Hither Asia, Australia) 

 but the group or subgenus to which Carolina belongs is strictly American and Walter 

 Horn was so skilled a specialist in Tiger-beetles that he could not possibly have 

 identified the wrong group. It is therefore easily understandable that some students 

 (at least verbally!) expressed their doubts as to the authenticity of the specimen, ^ — 

 On other proposed North American elements from Baltic amber, vide Kolbe 



(1925)- 



The main impression of the Baltic amber fauna, if climatic differences from pre- 

 sent European conditions are disregarded, is its importance as a connecting link 



^ However also a small Silphid beetle, Nemadus colonoides Kr., is reported to have 

 remained unchanged since the time of the Baltic amber (Jeannel, 1942, p. 192). 



^ The specimen belonged to the Berendt collection of the Geol.-Palaeont. Inst., Humboldt 

 University, Berlin, but seems to have been lost. 



