110 



INVOLUTION OF MAMMALIAN MOLAR TEETH 



-Pa. 



-Me 



Upper Molars of the Left Side. 



FIG. 58, No. 1. Adaptive Radiation of the Tritubercular Molar Type in the Marsupialia. 

 From Bensley. (Cf. Fig. 58, No. -I.) 



a, b, c, Insectivorous type, re, Oligocene Opossum (Pi i-ut/n i-ium /"./.'); fr, Recent Opossum 

 (Diillpliys azai-if); c, l>nlt.l/>/i>/s ririiinianu. a, d, r/, Progressive carnivorous specialization. 

 </, Dnsimrus rii-ei-riitus; ft, 'J'lti/lacitnus ciinvreplinlus. e, Progressive insectivorous-omnivorous 

 type (Perameles imsi'tit) ; /, Omnivorous to herbivorous type (Petauroidex rolans). h, Incipient 

 lophodont, herbivorous type (Trirli*<n '"< fi'l/iiculu). i, Perfected lophodont, herbivorous type 

 (Mucropus sp.). j, Selenodont herbivorous type (Phascolttrctos cineri ex). 



of Perameles nasuta 1 (Fig. 58, c) show all the essential characters of 

 those of Da*>/nriix, and they show the addition of an incipient hypo- 

 cone ; in the third molar the hypocone is not very pronounced and 

 the tooth is still triangular ; but in the second molar the hypocone 

 is well developed and the tooth is now quadrate. Thomas (1888, 

 p. 220) describes the triangular and quadrate modifications as character- 

 istic of this family (the Bandicoots). The lower molars of Perameles 



1 The upper molars of Perameles macrura (Figs. 59, 60) closely resemble those of the 

 Insectivore Myoyale, as shown in unworn teeth ; thus they exhibit the many sharp cusps 

 and the double mesostyle characteristic of several insectivorous forms. 



