OLIGOCENE OF EUROPE, NORTH AFRICA, AND NORTH AMERICA 179 



sodactyls. A very similar modernization occurs in western Europe, many 

 familiar modern families appearing for the first time. 



Several of these new families appear simultaneously in Europe and 

 North America. Thus the two countries which were separated most widely 

 at the close of the Eocene are again brought together in the Lower Oligocene, 

 as shown in the accompanying table. 



Mammals of the Lower Oligocene 



Peculiar to 

 Europe 



Palaeotheres 



Anoplotheres 



Csenotheres 



Gelocids 



Amphicyonids 



Viverrids 



Cricetines (ham- 

 sters) 



Theridomyids 



Sirenians {Hali- 

 therium) 



Common to Europe and 

 North America 

 Titanotheres 

 Chalicotheres 

 Rhinoceroses (aceratheres 



and diceratheres) 

 Amynodonts 

 Anthracotheres 

 Suillines 

 Entelodonts 

 Opossums 

 Hysenodonts 

 Canids (dogs) 

 Mustelids (martens) 

 Machserodonts (saber-tooth cats) 



Peculiar to North 

 America 

 Horses 



Hyracodonts (rhinoceroses) 

 Oreodonts 

 Camelids 

 Hypertragulids 

 Leptictids 

 Chrysochlorids ? (insecti- 



vores) 

 Ischyromids ^ (rodents) 

 Leporids or hares 



The closest correspondence of the Old and New Worlds is seen to be 

 among the perissodactyl ungulates and the carnivores; the least community 

 is among the artiodactyl ungulates, which exhibit fewer families in common. 

 It is a very striking fact that there was little interchange of the artio- 

 dactyls of the New and Old Worlds until the Pleistocene. 



We note that forest and browsing quadrupeds prevail in both countries. 

 A contrast is the apparent disappearance of the horses in western Europe, 

 and the rapid evolution of these animals in western North America. The 

 continental influence of North America is still displayed in the presence of 

 giant quadrupeds, especially the titanotheres and entelodonts, which greatly 

 surpass in proportions the largest of European mammals of the time, which 

 are of intermediate and smaller size; there is also, on the whole, a greater 

 diversity in the American life. In the two countries six of the great families 

 of perissodactyls and artiodactyls of Eocene origin die out. The last of the 

 archaic carnivores (hyienodonts) survive only to the Middle Oligocene. 



' The Ischyromyidae, the American Eocene Rodentia par excellence, are regarded by 

 Matthew as a primitive Eocene and Early Oligocene {Ischyromys, Prosciurus, Cylindrodon) 

 group of squirrel-like or sciuromorph rodents. The great raasseter muscle of the jaw lies 

 entirely behind the infraorbital foramen, as it does in the existing sewellels (Haplodontidse), 

 also peculiarly American rodents, first observed in the Upper Oligocene, or John Day, and in 

 the specialized Mylagaulids, a peculiar family of horned rodents of the Upper Miocene, both 

 Sciuromorpha. 



