PALEONTOLOGY 129 



tion is true, they must have branched off from the 

 Amphibian stock early in its history and in all 

 of their long history they have made no progress. 

 And so I might continue through every class and 

 order of vertebrates. 



Reptiles of any living order are as simple in struc- 

 ture as were the oldest known reptiles of that order, 

 and, consequently, if birds and mammals were off- 

 shoots of the reptilian stock, they are a most remark- 

 able exception to the rule that reptiles have kept 

 right on from the first without making progress in 

 structure. 



The Ornithorhinchus, now living, is an older form 

 than the marsupials, and consequently we must seek 

 the first of its kind far back in the Paleozoic. It can 

 not differ much in structure from the monotremata 

 which preceded the marsupials. It might be called 

 an "immensely archaic " form of mammal, and yet it 

 survives, while some one of its kind, more fortunate 

 than the living species, shot upward in the line of 

 progressive organization and finally resulted iu man. 



One of the first great changes which the monotreme 

 made was to become a marsupial. The pouch of the 

 latter would have been useless until sufficiently devel- 

 oped to contain the young, and, as usual with rudi- 

 mentary organs, we are unable to account for its evo- 

 lution at all. 



The oldest known mammals were in the Triassic. 

 They were small insectivorous marsupials. The lower 

 jaw-bone of one from the Triassic of North Carolina 

 is about one inch long. But few remains of mam- 

 mals have been found in the Triassac, and they are 

 teeth and fragments of jaw-bones. 



In the Jurassic of both Europe and America the 

 teeth and jaws of a good many species of insectiv- 

 orous marsupials of the size of rats and mice have 



