Skull of Bauria cynops Broom, about one-half natiu-al size. 

 This is the most primitive of the very mammal-like reptiles belong- 

 ing to the group of Cynodonts. The dentition, it will be observed, 

 is like that of the mammal except in that the grinding teeth are 

 simply little pegs not unlike those found in the armadillo 



South African fossil 

 forms is that it was 

 probably the devel- 

 opment of the active 

 Cynodonts that led 

 to the development 

 of the active reptiles 

 such as Euparkeria. 

 For possibly two 

 million years the 

 carnivorous mam- 

 mal-like reptiles had 

 an abundant supply 

 of food in the form 

 of the small Anomo- 

 donts. In lower Tri- 

 assic times the small- 

 er Anomodonts seem 

 to have become ex- 

 tinct for some rea- 

 son and the carnivo- 

 rous forms had to 

 obtain a new diet 

 which was probably 

 a little lizard-like 

 animal called Pro- 

 colophon, and pos- 

 sibly other small 

 reptiles of a similar 

 type. It was possi- 

 bly this new activity 

 that gave rise to 

 the Cynodonts. In 

 upper Triassic times 

 the Procolophons be- 

 came extinct and 

 the small Cynodonts 

 were driven to at- 

 tacking the more active types like Euparkeria. The rivalry between 

 these forms resulted in the greatly increased activity of both, the active 

 four-footed forms becoming the primitive mammals and those which run 

 on their hind legs gave rise to the theropodous dinosaurs and the ancestral 

 birds. The further evolution of the bird was doubtless the result of its 

 taking to an arboreal habit and developing feathers. 



346 



Skull of Nythosaurus larvatus Owen, slightly reduced. This is 

 one of the most mammal-like of the reptiles belonging to the 

 Cynodonts. Were it not for the composite character of the 

 lower jaw it might readily be regarded as a mammal 



Aud. Gr. 



Skull of Sesamodoti browui Broom. This is another type of 

 cynodont reptile which is in some respects more like the mammal 

 than any other 



