94 ARKIV FÖR ZOOLOGf. BAND 14. ]Sr:0 4. 



Caenolestes among the Diprotodonts». The author quoted 

 further reminds about the fact that »a type of dentition may 

 remain practically unaltered throughout long ages, if the 

 habit remains the same», but on the other hand he points 

 ont »hovv readily the type may be altered with change of 

 habit». The present author is quite wilhng to agree about 

 this, but then it must on the other hand be admitted, that 

 if two mammals with different habits and different diet in 

 spite of this have a very similar dentition of much specia- 

 lised character^ this fact must speak strongly for some kind 

 of genetic conneotion, for the h'keness can in such a case 

 not be explained as due to adaptation in a parallel or con- 

 vergent direction. Now there is an undeniable likeness with 

 regard to the incisors of Caenolestes on one hand and those 

 of certain Phalangerids and Kangaroos on the other. The 

 forward directed knife-like ii with their upper cutting edges 

 fitting in between the lengthened cutting edges of i^ and 

 P so as to form scissors or shears constitute a much dif- 

 ferentiated apparatus moved in a similar way in both these 

 animals, as the shape of the condyles proves. These animals 

 have, however, quite different habits and entirely different 

 diet, and this peculiar type of dentition can thus not be 

 assumed as a product of independent convergent adaptation 

 both in the insectivorous Caenolestes and the graminivorous 

 Macropodidae. 



The following hypothese may be offered as an attempt 

 to explain the resemblance in dentition etc. between the ani- 

 mals mentioned. It is known by the investigations of Ame- 

 GHiNO, Sinclair a. o. that the early Marsupials of the Santa 

 Cruz beds had differentiated in at least three different direc- 

 tions one of which probably leads to the recent Didelphyidae, 

 and another in the present time is represented by Caeno- 

 lestes, while the third according to Sinclair points to affi- 

 nities to Thylacinus. In earlier times at least the two first 

 of these may have had a common origin, which explains 

 certain primitive »Didelphyoid» features in Caenolestidae. It 

 is according to my opinion most probable, that the Marsu- 

 pials of Australia have arrived to that continent from South- 



^ Primitive conditions can of course be retained independently in 

 widely distant groups, but in this case the dentition is speciaiised in a. 

 very remarkable degree. 



