340 VERTEBRATE ZOOLOGY 



brum) was small in proportion to the size of the body and was reptile- 

 like in many respects. 



These archaic mammals went the ways of the Mesozoic reptiles to 

 a considerable extent, in that they became large, robust, vegetative 

 mechanisms with low intelligence and little adaptability. Like the 

 dinosaurs they vanished completely from the face of the earth and 

 left few descendants. Only those of small size and with comparatively 

 unspecialized structures survived to become the ancestors of our 

 modern mammalian faunas. Osborn sums up the situation as follows: 

 "Nature deals in transitions rather than in sharp lines. We 

 can not circumscribe the archaic mammals sharply, nor be sure 

 as yet that some of them did not give direct descent to certain 

 of the modernized mammals. Yet the animals of the basal 

 Eocene of both Europe and North America are altogether of a 

 very ancient type; they exhibit many primitive characters, such 

 as extremely small brains, simple triangular teeth, five digits 

 on the hands and feet, and prevailing plant igradism. They are 

 to be collectively regarded as the first grand attempts of nature 

 to establish insectivorous, carnivorous and herbivorous groups, 

 or unguiculate (clawed forms) and ungulates (hoofed forms). 

 The ancestors or centres of these adaptive radiations date back 

 into the Age of Reptiles. At the beginning of the Eocene we 

 find the lines all separated from each other, but not as yet very 

 highly specialized. The specialization and divergence of these 

 archaic mammals continue through the Eocene period and reach 

 a climax near the top, although many branches of this archaic 

 stock become extinct in the Lower Eocene. The orders which 

 may be provisionally placed in this archaic group are the follow- 

 ing: 



"Marsupialia. 



Multituberculata, Plagiaulacidse. 

 Placentalia. 



Insectivora. Insectivores not yet positively identified in 



the basal Eocene. 



Tseniodonta. Edentates with enamel teeth. 

 Creodonta. Archaic families of carnivores. 

 Condylarthra. Primitive light limbed cursorial ungulates. 

 Amblypoda. Archaic, typically heavy limbed, slow- 

 moving ungulates. 



