APPENDIX 363 



but he claims that the phylogeny of most of the 

 other orders is known. 



The earliest known mammals (of the Triassic and 

 Jurassic) " are already highly specialized. They 

 probably represent the Monotremata of their time." 

 The fact that they were then " highly specialized " is 

 very significant. How long had it taken them to be- 

 come so? When did they depart from the reptilian 

 type? Paleontology is silent as to their origin. 

 Again, he says, " The immediate didelphian ances- 

 tors of the monodelphous Mammalia have not yet 

 been certainly discovered." How do we know then 

 that the ancestors were didelphian? 



Again, " The history of the Monotremata is not 

 made out, but the earliest forms of which we know, 

 the skeleton, Polymastodon (Cope) of the Lower 

 Eocene, is as specialized as the most specialized 

 recent forms. The dentition of the Jurassic forms, 

 Plagiaulix, etc., is quite specialized also, but not 

 more than those of the kangaroos. The premolars 

 are more specialized, the true molars less specialized 

 than in those animals."* 



From this it is seen that the oldest known mono- 

 tremes are found in the Eocene, and yet it is assumed 

 that monotremes were the ancestors of marsupials a 

 whole long age before the Eocene began. 



The oldest known forms of monotremes and mar- 

 supials were as specialized as living ones of the same 

 orders. 



Again, he says: "In conclusion, the progressive 

 may be compared with the retrogressive evolution of 

 the Vertebrata, as follows: In the earlier periods and 

 with the lower forms, retrogressive evolution has pre- 

 dominated. In the higher classes progressive evolu- 

 tion has predominated." t 



* Page 142. t Page 146. 



