ORDINAL TYPES OF MOLARS : PROTODONTA, ETC, 101 



In a general way these animals are conservative and exhibit some of 

 the earlier stages of trituberculy as well as the extreme specializations 

 for exclusively carnivorous and herbivorous diet. 



2. The second group includes the Primates, which are primarily 

 frugivorous and omnivorous. In a general way also, these monkeys 

 and lemurs are transitional between an earlier insectivorous and a 

 frugivorous and herbivorous diet; thus the study of their teeth forms an 

 admirable introduction to the study of the teeth of the Ungulata. 



3. The third great group includes all the hoofed animals or 

 Ungulata, of which the food is primarily herbivorous and secondarily 

 omnivorous in certain cases. In a general way again, the Ungulata 

 exhibit the extremes of complication of the crowns by cusp addition 

 and cusp modelling. 



4. The fourth great group includes the Cetacea, in which the teeth 

 are specialized for various kinds of sea food, or entirely wanting. 

 They exhibit what is probably a retrogressive dentition from an earlier 

 type, such as that presented by certain of the Unguiculata. 



PROTODONTA. 



The molar teeth of the Protodonta have been described on page 18 as 

 transitional from the haplodont to the triconodout condition. Similar 

 changes are observed among the Theriodontia, as described on page 

 91 ; and analogous changes, that is, the addition of lateral cusps to a 

 central cusp, have occurred frequently among the Vertebrata. 



It is possible that the Protodonta are not mammals ; but the in- 

 cipient division of the fang and the apparent absence of angular and 

 articular bones of the jaw render it probable that they are at least very 

 early types of mammals, probably of egg-laying habits, like the Mono- 

 tremes. A jaw somewhat resembling those of Dromatherium and 

 Microconodon has recently been described by Broom* in South Africa 

 from the Upper Beaufort Series (Karoo system), which are considered of 

 Upper Permian or Triassic age. 



SPEC I A L R INFERENCES. 



Osborn, H. F., "On the Structure and Classification of the Mesozoic Mammalia," 

 Journ. Acad. Nat. Sci. Phila. (2) IX., 1888, p. 222, antea, pp. 31-35. 



Osborn, H. F., " The Triassic Mammals, Ui-oniathtrium and Microconodon ; Proc. 

 Amer. I'lu'lns. Soc., Apr. 1887, <nit<', pp. 18-21. 



ALLOTHEKIA 01; MULTITUBERCULATA. 



Because the Multituberculata are among the oldest known mammals, 

 first occurring in the Knit-tic or Upper Triassic, it has been urged that the 



*Geol. M<i. Deo., IV., Vol. X., 190:?, p. 34r>. 



