PREHISTORIC ANIMALS 



431 



consist almost exclusively of jawbones and teeth, it is difficult 

 to fix their precise relationship to existing orders. Some appear 

 to have been related to the Monotremata and others to the 

 Marsupialia; they were of small size. The only mammalian 



_ ~ e*~~ <-»■*. 1 ■■■" ' 





FlG. 411. Ichthyornh viclor, a iossil ternlike bird of North America, skeleton, restored. 

 ( Alter Marsh, from Parker and Haswell's Text-book. I 



fossils in Cretaceous rock have been found in a few places in 

 North America. We can, therefore, form no detailed concep- 

 tion of the Mesozoic Mammalia. 



When we come to the Cenozoic era, we have a relatively 

 much shorter period of time to deal with. This has been esti- 



