86 MAMMALIAN DENTITION 



individual cusps are united to form crests. This is termed the 

 lophodont dentition and will be illustrated by examples from 

 the Kangaroos. In it the molar teeth tend to be long crowned 

 or hypsodont whereas in both other modifications so far con- 

 sidered (except in Thalacomys) the teeth are short crowned or 

 brachyodont. 



The three types chosen to represent the lophodont dentition 

 are the following: Potorous tridactylus, the common Rat Kan- 

 garoo of Eastern Australia and Tasmania (Fig. 25), Dendro- 

 lagus inustus, a Tree Kangaroo from New Guinea (Fig. 26), 



Fig. 25. — Dentition of Rat Kangaroo (Potorous tridactylus, 9.221-5). 



and Macropus bennetti, Bennett's Wallaby of Tasmania (Fig. 

 27). Potorous is a nocturnal animal living in the scrub jungle 

 and feeding on roots and bulbs as well as grass and leaves. 

 Concerning the habits of Dendrolagus little is known, but it 

 certainly feeds upon green shoots of the trees in Avhich it lives. 

 Macropus is the most advanced example and though varying its 

 diet with shrubs and roots it is in the main a grazing animal. 

 Examination of the photographs shoAvs that the dentition of 

 Potorous recalls somewhat that of Petaurus: the other two are 

 more specialized. Marked changes occur in all the teeth. The 

 upper median incisors, long though not procumbent in Poto- 

 rous, become shorter in Dendrolagus and equal in length the 



