LATE LAND CONNECTIONS IN THE NORTH ATLANTIC AREA 81 



bach (1959) seems inclined to remove a possible Eur-American "bridge" to 

 Pre-Tertiary time. 



Unfortunately, we do not know even approximately how old the animal 

 species are that now inhabit the Earth. The rate of evolution has been of quite 

 different magnitude in different groups as well as within different genera of the 

 same group. In spite of this, some idea of the minimum of time required for 

 the formation of a "new species" would be extremely valuable for the 

 dating of zoogeographical events. 



As far as insects are concerned it is safe to say that no evidence for species 

 formation in Pleistocene time has been brought forth. The fossils from Inter- 

 glacial or Interstadial deposits so far investigated (from Scandinavia, Great 

 Britain, and central Europe) seem in no case to be different from now living 

 representatives of the species. 



On the other hand, the insect fauna of Late Eocene, as amply illustrated by 

 thousands of very well-preserved fossils in the Baltic Amber, was quite 

 distinct on the species level. Most genera were identical with those of the 

 present time but very few are regarded as belonging to the same species 

 (e.g. among the Coleoptera, only one or two). 



Thus, species formation among insects in general seems to have taken place 

 after the Baltic Amber time, but before the Pleistocene, i.e. during a period of 

 between 40 and 1 million years ago. 



If the postulated North Atlantic bridge with its biota lasted only during 

 Early Tertiary and was broken down before the Oligocene period, and if 

 part of the present fauna and flora had survived from that remote time, then 

 there is no doubt at all that they would have contained a considerable number 

 of taxonomically well distinguished endemic species. For comparison we 

 need only refer to the numerous endemic insect species which survived, often 

 restricted to single mountain peaks, throughout the Pleistocene within the 

 massifs de refuge in the European Alps. 



Several biogeographers (e.g. Love and Love, 1956, p. 235, etc.; Larsson, 

 1959, p. 36, etc.; Einarsson, 1961, p. 46) have assumed that the land-bridge 

 persisted into Late Tertiary time with subsequent survival of the biota through 

 all Pleistocene glaciations. As far as I can see, however, old Tertiary faunal and 

 floral elements would have been left on Iceland and Greenland also in case 

 the bridge lasted into Pliocene time, with a peculiar flora in Iceland, rather 

 different from that of contemporary Europe (Jonsson, 1954; Schwarzbach 

 and Pflug, 1957, p. 289, etc.). 



It is also noteworthy that the shallow and narrow sound between Greenland 

 and Ellesmere Land in the High North was not used as a by-pass for the 

 Icelandic-Greenlandic Palearctic elements. This is easily understood if it is 

 assumed that the species in question immigrated from Europe as far as 

 Greenland during the Pleistocene, when the climate was never much warmer 

 than now. But it is much harder to realize that this northern connection would 



