196 INTRODUCTION TO EVOLUTION 



During the Eocene the archaic mammals had their brief period of as- 

 cendancy. Some of the archaic ungulates became quite large. The culmina- 

 tion in this direction was reached by the horned amblypod, JJintatherium 

 (Fig. 10.1). This creature was elephantine in size, though not in details 

 of structure. Creodonts, the archaic carnivores, somewhat resembled 

 wolves, weasels, cats, hyenas, and the like. 



The end of the Eocene saw the extinction of the archaic mammals. Ap- 

 parently they were not able to compete successfully with the more 

 progressive mammals developing around them. Lull (1945) has pointed 



FIG. 10.1. Uinfafherium, an archaic hoofed mammal. (After Osborn.) 



out that, as compared to the latter, archaic mammals were deficient in 

 structure of teeth, feet, and brain. In these features the archaic mammals 

 were conservative and inadaptable, unable to change with changing 

 conditions. 



Turning to the more progressive mammals, we find that the first rodents 

 and first lagomorphs appeared late in the Paleocene. The beginning of the 

 Eocene saw ungulates of the two orders existing today: Perissodactyla 

 (odd-toed) and Artiodactyla (even-toed). Members of the Condylarthra 

 were probably ancestral to these two orders. Indeed, representatives of 

 most of the orders of mammals appeared in either the Paleocene or the 

 Eocene, thus laying the foundations for evolution of these orders during 

 succeeding periods of the Cenozoic. Within the orders evolutionary 

 changes ran somewhat parallel courses. Ancestors in each were relatively 

 small, and were not specialized for particular types of food or for particular 



