72 MOSTLY MAMMALS 



goose-like chaja (pronounced chaha), or horned screamer, 

 which takes its English name from the spur on its wing 

 and its loud cry, the latter being sometimes heard when 

 the bird is so high in the air as to be almost or quite 

 invisible. The long-legged seriema, which stalks over the 

 plains in the manner of the African secretary-bird, is 

 like-wise a very characteristic type. Among characteristic 

 South American reptiles may be mentioned iguanas (a 

 name often applied incorrectly to lizards from other parts 

 of the world) and caimans ; the latter being a group of 

 alligators distinguished by having an armour of bony 

 plates on the under as well as on the upper surface of 

 the body. The huge horned frogs (Ceratophrys) are like- 

 wise distinctive of the country among the batrachians. 



Such are a few of the leading features of the existing 

 fauna of South America, which are sufficient to show how 

 totally different is the animal life of this country from 

 that of all the rest of the world. If, however, we go back 

 to the later geological periods of the earth's history, we 

 shall find that this peculiarity and distinctness of the 

 South American fauna was even more intensified than at 

 the present day, this being largely due to the circumstance 

 that at one time the isthmus of Darien seems not to have 

 existed, so that the northern and southern portions of the 

 New World were disconnected. Since the time when a 

 connection was formed between the two continents, their 

 faunas have, however, naturally tended to blend together, 

 and hence at the present day, and during the Pleistocene 

 period, the animals of South America are less sharply 

 differentiated from those of the northern half of the con- 

 tinent than would have been the case had the isthmus 

 of Darien not been formed. It is further interesting to 

 note that during the Tertiary period there appears to have 



