88 ORIGIN OF LIFE IN AMERICA 



California quite a peculiar yellow-billed magpie has arisen, 

 which is sometimes distinguished by the name of Pica nutalli. 



It is not at all evident that the ancestors of these American 

 magpies entered America by way of Alaska, and yet if mag- 

 pies had originated in America there would probably be many 

 species there ; at any rate, they would inhabit the whole of the 

 continent, and perhaps central America as well. Being con- 

 fined to the west, and differing but slightly from Old-Worfid 

 forms, their origin points to Asia. At the same time the fact 

 that the American magpie is more like the European form 

 than the Asiatic one is a feature which cannot be lost sight 

 of. Dr. Diederich discusses the problem whether the 

 American magpies arrived in America before or after the 

 Glacial Epoch. In spite of the fact that magpies in America 

 are entirely migratory and have lived on the continent suffi- 

 ciently long to develop the peculiar Californian race just 

 referred to, Dr. Diederich * inclines to the belief that they 

 entered the New World in post-Glacial times. Without any 

 fossil or other evidence to guide us, it is difficult to express 

 an opinion on this subject. But it seems to me that the 

 magpie should be placed into one group with a good many, 

 other forms of animal life which reached North America long 

 before that event, as I shall more fully describe in one of 

 the subsequent chapters. 



Dr. Gill, as I mentioned above (p. 83), expressed the 

 opinion that the occurrence of Scaphirhynchus in Asia pointed 

 in favour of an older land connection between that continent 

 and North America. The fish known in America as the 

 shovel -nosed sturgeon (Scaphirhynchus platyrhynchus) is 

 abundant in the river system of the Mississippi to which it 

 is confined. It is now known that its nearest relatives are 

 two species inhabiting central Asia which are no longer classed 

 with Scaphirhynchus, but are placed into the distinct genus 

 Kessleria. All these ganoid fishes belong to a very ancient 

 group, most of which are extinct. The skeleton of the 

 ganoids is generally cartilaginous, and they retain many 

 other archaic characters in their anatomical structure. 

 Another example is the paddle-fish (Polyodon spathula). It 



* Diederich, F., " Verbreitung der Elstern," p. 51. 



