340 



HISTORICAL GEOLOGY. 



But, as the first birds were not true typical birds, but 

 reptilian birds, so also the earliest mammals were not true 

 typical mammals, but reptilian mammals, or marsupials. 

 The marsupials live now almost wholly in Australia. They 

 include the kangaroos, the opossums, the bandicoots, the 

 wombats, etc. In Jurassic times they apparently inhab- 

 ited all parts of the earth in great numbers. Now, the 



marsupials differ so 

 gi-eatly from ordinary 

 mammals that they are 

 put into a distinct sub- 

 class. One striking pe- 

 culiarity about them is 

 that their young are 

 born in an exceedingly imperfect state, so that they are 

 almost egg-bearing, semi-oviparous. 



But neither were the Jurassic marsupials typical mar- 

 supials, but rather generalized types connecting with In- 

 sectivora, the lowest of the true mammals. They were all 

 small animals, varying in size from that of a mole to that 

 of a skunk. They were not able to contend for mastery 

 with the great reptiles. The reign of mammals had not 

 yet come. We give here (Figs. 289, 290) a jaw of a Ju- 



FIG. 289. Jaw of a Jurassic mammal 

 Amphitharium Prevostii. 



FIG. 290. Myrniecobius fasciatus, banded ant-eater of Australia. 



