6io THE PLIOCENE PERIOD 



When connection between the two Americas was made in the 

 Pliocene, the fauna of each continent invaded the other. Horses, 

 mastodons, deer, carnivores, and tapirs from the northern continent 

 went to the southern, while gigantic sloths from the south came to 

 our continent, though they did not maintain themselves long. 



The herbivores had the foremost place among mammals; both the 

 odd- and even-toed ungulates evolved their present orders, and many 

 of their present genera. They were represented also by many 

 genera and species which are now extinct. The evolution of the 

 horse was advanced to the existing genus Equus. Giraffes and 

 giraffe-like animals, some of them of great size, invaded southern 

 Europe and Asia, probably from Africa. 



The giants of the period were the proboscidians. The extinct 

 Dinotherium was widely distributed in Europe and has been found 

 in India, but is not known to have reached America. Mastodons 

 seem to have lived in all the continents, but it is doubtful whether 

 elephants reached America before the Pleistocene. They appear 

 to have flourished in Europe, and, with the associated rhinoceroses 

 and hippopotamuses, gave the European Pliocene fauna an African 

 aspect. 



Carnivores throve and perhaps gained on the herbivores; at any 

 rate they put a severe tax on the herbivores, forcing further progress 

 in the line of alertness, sagacity, speed, and defense, and gaining 

 similar qualities themselves. 



Great interest attaches to the development of the primates 

 (monkeys, apes, man), but the data on this point are likely to re- 

 main limited until the tropical regions of the Old World, where the 

 chief evolution of this group seems to have taken place, are more 

 fully studied. No remains of lemuroids or of their descendants 

 have been found in the Pliocene of North America, and those of 

 Europe are from the middle and southern parts of the continent, per- 

 haps implying that northern Europe was too cold for these animals. 



Some years ago a man-like skeleton was found in what were then 

 regarded as Pliocene deposits in Java, and named Pithecanthropus 

 erectus. The find included the roof of a skull, two molar teeth, and 

 a femur. The form of the femur indicates that its possessor walked 

 erect. The forehead was low and the frontal ridge prominent, and 

 in general the characteristic features were intermediate between 

 those of the lowest men and the highest apes, as shown in Fig. 503. 

 The size of the brain was about two-thirds that of an average man. 



