LIFE HABITS AND DENTITION 



79 



which are of necessity mixed with earth must entail greater 

 wearing of the molars than the purely insectivorous or carniv- 

 orous habit. In Thalaeoniys this has been provided for by the 

 marked elongation of the body of the tooth, one variety of a 

 condition known as hypsodonty. In other animals the term 

 hypsodonty is used to indicate marked elongation of the cusps 

 themselves. 



A much more general form of omnivorous dentition is that 

 presented by Petaurus breviceps the Lesser Flying Squirrel 



Fig. 22. — Dentition of Lesser Marsupial Flying Squirrel. (Petaurus breviceps. 

 9.222-3). Example of an omnivorous dentition forecasting in many features the evolu- 

 tion of the herbivorous adaptation. Note the elongated lower median incisors and the 

 quadrilateral crowns of the molars with their four rounded cusps. 



(Fig. 22). It is true that the parachute flight of this animal 

 indicates a certain specialization but its dentition is stated to 

 be the same as that of its nonvolant parent form Gymnobelid- 

 eus. Naturally, in spite of its name this creature is not a squir- 

 rel at all but a phalanger. It has a dentition most important in 

 the present connection because it foreshadows the method of 

 evolution of the truly herbivorous adaptation. 



