THE RECORD FROM FOSSILS. 



Ill 



portant group. It would seem that somewhere toward the close of 



the Cretaceous (8), or perhaps earlier, these animals made a further 



improvement upon their method of producing young. They devel- 



M BRA F 



C , 



FIG. 14. M Mammals. B Birds. R Reptiles. A Amphibiane. F Fishes. 



oped the placenta which enabled them hereafter to carry their young 

 in the uterus till it was well developed. The placental mammals thus 

 arising proved to be a much stronger type than that which had existed 



