72 AFFINITIES AND HABITS OF THYLACOLEO, 



unreliable, the lower incisors are quite unlike those of the 

 herbivorous Diprotodonts. In svich typical forms as the Wom- 

 bat, the Koala, the Kangaroo, and the Phalanger, though there 

 are different modifications of the arrangement, we have the lower 

 incisors meeting the up2:)er and forming with them an instrument 

 for biting through a moderately tough fibrous tissue, and even in 

 the very small Diprotodonts, so far as I am aware, the lower 

 incisors always meet and work against the upper. But in Thyla- 

 coleo we have powerful pointed incisors which do not meet, but 

 overlap. Though technically incisors they are not intended to 

 incise, but to pierce and tear. Such powerful pointed and over- 

 lapping teeth, though easily explained on the theory that they 

 were intended to kill and tear animal prey, were never surely 

 provided merely to pierce succulent vegetables or ripe fruit. It 

 might of course be argued that the incisors were used as weapons 

 of defence, as apparently are the canines in the Baboon ; but 

 against this idea is the objection that the incisors were put to 

 some use which wore them down and blunted them more rapidly 

 than would be the case if they wei'e chiefly used on the rai'e 

 occasions when the animal had to defend itself, and furthermore 

 were such the case the temporals would not require to be greatly 

 developed. 



There is thus, in my opinion, no other conclusion tenable than 

 that Thy lacoleo was a purely carnivorous animal and one which 

 would be quite able to, and probably did, kill animals as large as 

 or larger than itself. 



Let us now consider how such a huge carnivorous animal 

 might be developed from an herbivorous Diprotodont Phalanger. 

 Though Burramys comes nearer to Thylacoleo than does any 

 other known form, it could not itself have been a direct ancestor 

 for the following reasons. In the masseteric fossa of 'I hylacoleo 

 is a small foramen which opens through to the inner side of the 

 jaw. In most of the living Phalangers this is lost, though it is 

 still retained in Fetaiirns, and becomes enormously enlarged in the 

 M acropodidof.. In Burramys it is also lost, and it seems very impi'o- 

 bable that when once lost it could be reproduced in a descendant. 



