CHAPTER X 
THE FAUNA OF CENTRAL AMERICA 
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 fail 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. R., “ Distribution of Animals,” Vol. II., pp. 57—59. 
