436 THE GENERAL PRINCIPLES OF ZOOLOGY 



allied to the gibbons and gorilla occur in the Miocene, to the 

 orang and chimpanzee in the Pliocene. In the Miocene of India 

 flints have been found which appear to have been of human man- 

 ufacture ; in the Upper Pliocene of Java there were discovered 

 in 1894 portions of the remains of an animal which has been 

 called Pithecanthropus erectus ; by some scientists it is regarded 

 as belonging to a low race of man, by some as a large, manlike 

 ape, while others considered it as intermediate between the 

 higher apes and man. If the first of these three views is cor- 

 rect, then the earliest human remains as yet discovered date 

 back to the Pliocene ; if the others are correct we have no actual 

 remains until the Pleistocene. 



If we consider the entire class of Tertiary Mammalia, we are 

 most impressed with the generalized type of structure which its 

 representatives present, a phenomenon which holds in general 

 for all animal classes when they first appear in fossil remains. 

 As we pass from the earlier to the more recent mammals, each 

 group tends to higher and higher specialization as it approaches 

 existing species, a fact which will be more apparent when we 

 come to consider Post-tertiary animal life. 



The Quaternary or Post-tertiary period has been estimated 

 to occupy about one twentieth of the period of time which has 

 elapsed since the beginning of the Cambrian, and to be about 

 half as long as the Tertiary. Very many species which exist 

 to-day are represented in the Pleistocene fossils, and likewise 

 many extinct species. The glacial period which occurred at 

 this time affected profoundly the geographical distribution of 

 animals, for many species which until then occupied the 

 northern hemisphere, in what are now its temperate and 

 Arctic regions, afterward are found only in tropical regions, 

 the great cold having caused them to migrate southward. 

 There are fossils of some interesting birds which lived in the 

 Pleistocene and became extinct during that period or in the suc- 

 ceeding Recent. These birds were wingless or had rudimentary 

 wings, and hence were incapable of flight, and some of them 

 attained an enormous size. The genus Dinornis (Fig. 414) of 

 New Zealand contains species which stood three meters high. 

 Other species of this same genus, although not so tall, had very 

 massive skeletons, the toe bones almost rivaling those of the 



