GEOLOGICAL SUCCESSION OF MOLAR TYPES 



99 



trituberculy into higher forms of molar teeth as described in othci 

 chapters (see pp. 37, 45, 132, 151, 158, 170, 171, 175, 178). 



RESUME OF GEOLOGICAL SUCCESSION OF TYPES. 



It does not appear necessary to present any further proofs of the fact 

 that apart from the Multituberculates the geological succession of types of 

 molar teeth presents so few exceptions to the main law of trituberculy and 

 the principle of cusp addition that these exceptions may be designated as 

 aberrant. The advance of the teeth from type to type corresponds with 



the advance of geological time as follows : 



UPPER MOLAR TYPE. 



MAXIMUM TOTAL OF CUSPS 



IN ONE PAIR OF 

 UPPER AND LOWER MOLARS. 



Triassic, 



6 



Haplodont, Protodont, Tri- 



conodout, with single or 



grooved fangs, 

 Jurassic, Triconodont, Tritubercular, 



with 2 or 3 fangs, 8 cusps, 1-2 styles. 



Cretaceous, Tritubercular, 11 cusps, 2 styles. 



Basal Eocene, Tritubercular, Quadrituber- 



cular, and higher stages, - 12 cusps, 3-4 styles. 

 Upper Eocene, Tritubercular and all the 



derived types, 12 cusps, 6 styles. 



