AMERICAN PTARMIGANS 63 



enter a belt of more or less stunted timber before reaching the 

 real forest. Yet even here quite a number of new forms of 

 animal life are met with that are quite absent in the more 

 northerly districts. They are mostly species occurring also 

 in the forest zone of western Labrador. In referring to them 

 in the last chapter, I alluded more fully to the geological 

 history of the moose (pp. 32 33), but I dwelt also on the fact 

 that the flying squirrel, musk rat, chipmunk, woodchuck and 

 others made their appearance as soon as we entered the 

 forest from the east. And it is precisely these forms of animal 

 life that make such a change in the Appearance of the fauna 

 as we leave the Mackenzie region barren-grounds on our 

 way to the great Canadian forest region. 



The flying squirrel (Sciuropterus sabrinus) of northern 

 Canada and arctic America is also found further south. Other 

 species of the same genus inhabit the United States. The 

 skin at the sides of its body extends between the limbs in 

 such a manner as to act like a kind of parachute, but nothing 

 in the nature of actual flight takes place. The flying 

 squirrel is rarely seen, being an entirely nocturnal crea- 

 ture. The distribution of these flying squirrels is decidedly 

 interesting. They are found from Florida to Alaska, and 

 are only known as fossils from the Potter Creek Cave in 

 California. They have almost certainly been in the country 

 since Pliocene -times. Hence Sciuropterus yukonensis, which 

 is peculiar to Alaska, lias, in all probability, survived the 

 Glacial Epoch in that country. On the western side of Bering 

 Strait, in Kamchatka, another species is found whose range 

 extends westward as far as Scandinavia. Southward, as 

 we cross China into Burma and India, we still encounter 

 species of flying squirrels, and even on the islands of 

 Java, Sumatra and Borneo. And all these belong to the same 

 genus Sciuropterus. Such an extensive distribution implies 

 that the genus must be an ancient one, and, indeed, we are 

 acquainted with several species of Sciuropterus from the 

 Miocene and Pliocene deposits of France. This in itself is 

 no proof that the flying squirrels originated in Europe. They 

 may 'have spread there from Asia in later Tertiary times and 

 have subsequently died out in Europe, only to be re-estab- 

 lished more recently from a later Asiatic invasion. In any 



