Marsh Collection, Peabody Museum. 335 



tivores, Kodents, Primates, etc. There is as yet little or no 

 evidence which throws any light upon their origin, and until 

 the Cretaceous ancestors of the Monodelphs are more certainly 

 known, the problem will of necessity remain obscure. 



There appears to be a sort of vague belief that the Car- 

 nivora have arisen from the Insectivora, and one frequently 

 hears the expression " Insectivore-creodont ancestors." Now, 

 as a matter of fact, the Insectivora, as we at present know them, 

 are not more primitive than a large majority of the Creodonts ; 

 but on the contrary, with very few exceptions, all the living 

 Insectivores are considerably specialized, and even those that 

 do exhibit a more or less generalized structure are far removed 

 from the typical, ideal ancestor of the Carnivores. ]^or do 

 the few known fossil Insectivores help us much towards such 

 a belief, for in all of them, as far as we know, the peculiar con- 

 formation of the anterior part of the skull is almost as strongly 

 marked as it is in their living representatives. The very 

 general enlargement of the premaxillge and modification of the 

 incisors, with the reduction or disappearance of the canine, 

 constitute one of the striking osteological peculiarities by means 

 of which they may nearly always be distinguished from any 

 known Creodont or Carnassident. 



It would appear from the present trend of the evidence that 

 we shall be compelled eventually to return to the old idea of a 

 direct Marsupial ancestry of all the Monodelphian orders. By 

 this I do not mean to imply that the living Marsupials are 

 these ancestors, for the reason that they have in all probability 

 secondarily acquired a number of modernized features which 

 remove them considerably from the hypothetical progenitors. 

 Their peculiarities in the matter of the replacement of the 

 teeth, the increased number of incisors in the carnivorous and 

 insectivorous forms, and the inflection of the angle of the jaw, 

 we may readily believe to have been acquired, and did not 

 belong to their Mesozoic ancestors. In fact it has already 

 been shown that the increased number of incisors is due to a 

 development and partial retention of a first and second set. 



Whatever may be said of the derivation of the other orders, 

 the Mesozoic representatives of the carnivorous Marsupials 

 are not far removed from the hypothetical forms, to which, it 

 seems to me, the present evidence points with no doubtful 

 signs, as the ancestors of the Carnivora. Although we know 

 them from but a few fragments, yet the striking resemblances 

 which these bear to the corresponding parts of the living 

 carnivorous Marsupials, leave little doubt that their structure 

 was very similar. If we subtract from the skeleton of some 

 of the more typical living Marsupial Carnivores, such as the 

 Sarcophiles, Dasyures, Thylacynes, and Opossums, those char- 



