CHAPTEE X 



THE FAUNA OF CENTEAL AMEEICA 



The problems presented by a study of the fauna of Central 

 America are of the utmost significance in our investigations 

 into the origin of the American fauna as a whole. Even 

 the casual observer cannot tail to perceive that certain animals 

 from each of the two great continents lying to the north and 

 south of Central America, tend to spread along the narrow 

 isthmus, and thus intermingle with one another. When we 

 look at Dr. Wallace's map of what he calls the " Neotropical 

 Region," and notice how the South American fauna has 

 apparently invaded the whole of Central America, and even 

 crept northward along the lowlands of Mexico, so that the 

 triangular table-land of that country, with its northern in- 

 habitants, looks as if it had been forced like a wedge between 

 the two wings of the southern army of invaders, the whole 

 history of events seems to be clearly unfolded before our eyes. 

 Apparently, quite a simple zoogeographical problem, and one 

 that is easily soluble by a study of the distribution of existing 

 animals. Thus it seemed to Dr. Wallace. Of the geology of 

 Central America nothing was known when he wrote his 

 famous work on the distribution of animals. Nevertheless, 

 he argues (pp. 10 — 13), from the sudden appearance in' post- 

 Tertiary times of numerous South American forms of 

 edentates in temperate North America, and from such facts 

 as the occurrence of some identical species of sea fish on the 

 two sides of the Central American isthmus, that the union 

 of North and South America must be a comparatively 

 recent event, and that these continents must have been sepa? 

 rated during Miocene and Pliocene times by a wide arm of the 

 sea. When the evidence of both land and sea animals support 

 each other as they do here, adds Dr. Wallace,* the conclusions 



* Wallace, A. E., " Distribution of Animals," Vol. II., pp. 57—59. 



