Early Birds and Mamimds 



Throughout the Jurassic period, and it may 

 be added throughout the Cretaceous as well, 

 the mammals, so far as we know, were all 

 small, and belonged to those low types, the 

 monotremes or the marsupials. Also, these 

 were all of insectivorous or carnivorous habits, 

 for no remains have as yet been found to in- 

 dicate that any herbivorous mammal existed 

 before the Eocene period. These conditions 

 prevailed not only in North America, but ap- 

 parently the world over. 



To-day these groups of animals are almost 

 confined to Australia and a few of the adjoin- 

 ing islands — almost, but not quite, for a few 

 species of opossums are still to be found in 

 America, and one in the United States, and the 

 common opossum may justly claim to belong 

 to the first family of Virginia. The mammals 

 of Australia, with two or three trivial excep- 

 tions, are marsupials^ although in variety and 

 size they have progressed far beyond their 

 primitive ancestors. This shows that at an 

 early date in the history of mammals this great 

 continental island was cut off from all othei* 



191 



