50 



EVOLUTION OF MAMMALIAN MOLAR TEETH 



oldest monkey or lemur known, Anaptomorphus, which illustrate the 

 loss of the antero-internal cusp or paraconid, pa' 1 , this is present as a 

 rudiment in m l and m 2 , but has disappeared in ?/? 3 . This accounts for 

 the history of all the cusps in the human lower molar. Thus in the rich 

 series of Mesozoic l and lower Eocene Mammals we can observe the actual 

 rise, succession, and decline of all the six cusps, and do not require any 

 new hypothesis to explain their appearance. 



Dr. Rose supports his fusion hypothesis by a reference to the Multi- 

 tuberculates (p. 101); he could hardly have made a more unfortunate 



me" 



en 



FIG. 38. Evolution of the cusps of the Human Lower Molar. [1. Simple conical, reptilian 

 tooth. 2. Dromatherium. 3. Microconodon. 4. Spalacnthd-ii'tn. 5. Amphith<.riv.in. 6. Minds. 

 7. Anaptomorphus. 8. Homo.] 



choice, because between the little pauci-tubercular Microlfxtf* of the upper 

 Triassic and the multi-tubercular Neoplayimdax of the lower Eocene we 

 can follow the successive addition of tubercles with ease. I expect soon 

 to demonstrate that the molars of this aberrant group were also of 

 tritubercular, i.e. haplodont origin.* 



It is a striking fact that all t the molars of the Triassic and Jurassic 

 periods are distinguished by one conic cusp much larger and more 

 prominent than the others which are smaller and upon a lower level. 

 What are the positions and homologies of this cusp in the upper and 

 lower teeth '. 



1 See the Memoirs of Owen and Osborn upon the Mesozoic Mammalia. 

 *[See, however, the later views expressed on page 105, foot note. ED.] 



t[Even in MirroleNtes one cusp is higher than the others. (See Fig. 48, p. 102.) But 

 too much importance should not be attached to this fact. ED.] 



