COMPARISON OF EOCENE FAUNAS 191 



They appear as full-fledged rodents of the squirrel family in Paramys, in 

 the Wasatch beds. None of this type reached South America before the 

 Pliocene. In an equally sudden manner Hystricomorphs appear in the 

 Oligocene (Deseado = Pyrotherium) beds in South America. The first 

 forms belong mostly to the genus Cephalomys; in the Miocene there are 

 four families represented, and today six, cavies porcupines, chinchillas, 

 capybaras, etcetera. Hystricomorphs are also known from the Oligocene 

 of France and Africa, those from France being the older. In some way 

 they got to South America. It is the only group for which a land bridge 

 would need to be postulated, and on this alone few of us would want to 

 postulate such an earth's upheaval, for over it would have come or gone 

 no other forms. 



The North American Palasocene has yielded but few Primates, Indro- 

 don being the best known. Ameghino described a large number from the 

 Notostylops beds, but most of them have since been assigned to the Typo- 

 theres. Undoubted primates begin in the Colopdon beds (early Oligo- 

 cene) in Clenialites, which is followed by the well known Homunculus in 

 the Miocene, a typical member of the Cebidse. In later beds they increase 

 in size, and today two families of South American primates are recog- 

 nized, the Cebidse and marmosets, the two being usually united with the 

 Old World monkeys to make the Anthropoidea. To my mind, this is a 

 misleading classification, for the South American Primates diverged from 

 the Old World Primates in basal Eocene times and have never since 

 gotten farther from their homeland than Central America. The inde- 

 pendent history of these tAvo phyla should be recognized in their nomen- 

 clature, these New World forms being as much pseudo-monkeys as the 

 litopternas are pseudo-horses. 



So far the discussion has referred to less than half the Notostylops 

 fauna. The rest of iit is herbivorous and is usually designated as Notung- 

 ulata, including the litopternas, typotheres, toxodonts, astrapotheres, and 

 homalodotheres. At the beginning of the Eocene, North America also 

 had its group of herbivores, the collective assembly grouped as Condy- 

 larthra. The Notostjdops fauna includes a large number of such types as 

 Didolodus, Othneilmarshi, Asmithwoodwardi, and Lambdaconus, Avhich 

 are so like the C*ondylarthra that Ameghino (I think correctly) has 

 placed them in this order. Though the material is fragmentary, there 

 can be little doubt that these two groups had a common ancestry. From 

 this first herbivore group arose in North America the Perissodactyls and 

 Amblopoda, the one grass-eaters, the other browsers. Similarly, in South 

 America there came from the common group difPerent phyla adapted to 

 different types of vegetation. 



The grazers made a very progressive series, running through Deutero- 



