290 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1951 



{Cryptobranchus) related to the giant salamander of Japan; the 

 shovel-nosed sturgeon {Scaphirhynchus) with relatives in central 

 Asia; and the mud puppies (Necturus) and mud minnows {Umbra) 

 with relatives in southeastern Europe are localized remnants of types 

 that in the distant past were widely and generally distributed. 



As examples of an animal type abundant and widespread but 

 now greatly reduced in range and numbers, the camels may be men- 

 tioned. Camels originated in western North America where they 

 were formerly abundant and diversified. From this center they 

 spread to South America and Asia. They have now disappeared 

 except for four forms in South America and two in Asia, one of 

 which has been introduced into Africa. Two of the South American 

 species and both the Asiatic are known only as domesticated animals. 



PRESENT-DAY GEOGRAPHY 



In Alaska the Arctic barrens of Asia are continued and range 

 eastward to Ungava and Labrador, increasing in extent eastward, 

 beyond the mouth of the Mackenzie River, and reaching Churchill 

 on the western shore of Hudson Bay and nearly to James Bay on the 

 southeastern shore. The mountains of Alaska run east and west 

 continuing those of northeastern Asia (the Anadyr and Kolyma 

 ranges) , but in southeastern Alaska and Yukon they turn southeast- 

 ward, maintaining the same direction to the Guatemalan highlands. 

 The eastern highlands of North America run from the Gulf of St. 

 Lawrence to northern Georgia in a southwesterly direction. In the 

 western mountains arctic, or at least boreal, conditions occur at 

 increasingly high altitudes to southern California, Arizona, and New 

 Mexico. In the east less extreme but still northern conditions range 

 southward in the mountains to northeastern Georgia. 



From the Arctic Ocean to the Gulf of Mexico the central part of 

 North America is low with no natural barriers, so the grasslands, and 

 in the west the deserts, extend from Mexico and the Gulf far north- 

 ward into Canada. This absence of barriers facilitates the northern 

 or southern extension of the ranges of animals so that the distribu- 

 tional picture over most of the area in certain respects suggests that of 

 Africa or Australia rather than that of Europe or Asia. Except for 

 the Rio Grande, the rivers and lakes of North America are all cold, or 

 at least cool. Nearly all are northern. The Mississippi River with its 

 tributaries drain an area that is cool to very cold in winter so that its 

 waters are not suitable for the types of fishes inhabiting the warm low- 

 land rivers of southern Asia or the fresh waters of Africa or South 

 America. 



Continental Central America is remarkable for the diversity of its 

 physical conditions. The land includes extensive low areas near sea 



