XXVIII 



PROTOUNGULATES 



1 . Origin of the ungulates 



No herbivorous eutherians are known from the Cretaceous period, 

 but during the Palaeocene epoch a number of animals abandoned the 

 insectivorous habit and began to eat plants. These condylarths rapidly 

 radiated into numerous types, so that by the end of the Palaeocene 

 several distinct orders descended from this stock can be recognized. 

 In North America and elsewhere there appeared large, clumsy ani- 

 mals, the *Pantodonta (Amblypoda) and *Dinocerata, while in South 

 America a special fauna, the *Notoungulata and *Litopterna, de- 

 veloped. Further types then arose in the Eocene, including the early 

 elephants and Perissodactyla. The Artiodactyla first appeared in the 

 lower Eocene, as rather pig-like creatures; their origin is uncertain 

 but they may have come from some form not very distinct from the 

 *Condylarthra. 



During the Eocene and Oligocene there were, therefore, numerous 

 large, heavy-bodied herbivorous mammals, perhaps mainly suited to 

 forest life and living upon relatively soft green food, since their teeth 

 were mostly not highly developed for grinding. They were, however, 

 gradually replaced during the Miocene by swifter, grazing animals 

 suited to the plains of that period. 



Following Simpson we shall classify the numerous orders of her- 

 bivorous (ungulate) mammals into four superorders. The Proto- 

 ungulata, including *Condylarthra, *Litopterna, *Notoungulata, 

 *Astrapotheria, and Tubulidentata, include the oldest forms, together 

 with various early offshoots and one living creature the aardvark 

 or Cape ant-eater, which is difficult to place elsewhere. A second 

 superorder, Paenungulata, includes a number of descendants of the 

 condylarths that early achieved success, the *Pantodonta and *Dino- 

 cerata of the Holarctic region, *Pyrotheria of South America, and 

 *Embrithopoda in Africa. With these are placed the Proboscidea, 

 which succeeded them as large herbivores in the Miocene. The conies 

 (Hyracoidea) are an isolated group that still shows some of the Eocene 

 characteristics of this Paenungulate group, and the sea-cows (Sirenia) 

 are an early offshoot that took to aquatic life. Finally, the orders 

 Perissodactyla and Artiodactyla occupy two separate superorders, 

 Mesaxonia and Paraxonia. 



