Marsh Collection, Peabody Museum. 429 



know, at the same time, in localities so widely separated as 

 Europe and America. 



If, now, we examine these problems from the standpoint of 

 the distribution of the ancient mammalian faunae in the North- 

 ern Hemisphere, we reach conclusions so strikingly similar, 

 that the two classes of facts taken together constitute such a 

 basis or groundwork of probability, that we may feel reasonably 

 safe in locating the place of origin of both the higher plants 

 and certain mammals, at least, within the polar regions.* 



The facts of mammalian distribution in the Northern Hemi- 

 sphere may be briefly stated as follows : Early in the Mesozoic, 

 there appeared small mammal-like forms, which were widely 

 distributed over both the Northern and Southern Hemispheres. 

 Representatives of these species continued throughout the Cre- 

 taceous, and finally disappeared in the early stages of the Ter- 

 tiary. From these forms the modern Marsupials undoubtedly 

 had their origin. Many of them are classified in the group Multi- 

 tuberculata, which without much doubt finds its nearest living 

 representative in the Duckbill of Australia. It should be here 

 stated that with very few exceptions all these forms are repre- 

 sented by fragments of jaws and teeth. In one instance, how- 

 ever, a fairly complete skull is known (Tritylodon) from the 

 Karoo beds of South Africa. The teeth of this species are 

 astonishingly like those of many types in the Northern Hemi- 

 sphere, and hitherto it has always been classified in this group. 

 Seeley has shown that the organization of the skull presents so 

 many reptilian characters as to cause him to refer it to the 

 Reptilia. If this reference is correct, then in the absence of 

 any facts to the contrary it is highly probable that all the 

 Multituberculates are as much reptile as mammal. Indeed, it 

 is not easy to say at first glance upon which side of the line 

 living Monotremes should be placed. There can be little 

 doubt that, when more fully known, these ancient fossil types 

 will present every conceivable gradation between these two 

 great divisions of the Vertebrata. 



One fact in connection with these Mesozoic forms stands 

 out clearly and distinctly, and that is that as far as we are per- 

 mitted to judge from their fragmentary remains, the progress 

 of their evolution toward any of the higher mammals was very 

 slow indeed. The amount of change registered by their teeth 

 throughout the greater part of the Mesozoic is comparatively 

 insignificant. On this account it is inconceivable that any of 

 the species with which we are at present acquainted should be 

 regarded in the light of ancestors of the higher types, or 

 Eutherian Mammalia. 



* Some very noted botanists have held this view of the origin of the Angio- 

 spercns within the polar regions ; thus Gray, Saporta, and Nathorst were con- 

 vinced of its truth, and Dawson thought it probable. 



