1898] MAMMALIA IN EUROPE AND NORTH AMERICA 329 



Base of Gainozoic or Tertiary 



The members of this earliest Tertiary mammal fauna, so far as 

 can be determined from fragments, are remarkably similar on the 

 two sides of the Atlantic Ocean. Their remains are found in a lake- 

 deposit, the so-called Puerco Formation of New Mexico, and in the 

 Cernaysian Formation near Eheims, in France. Among them there 

 are still some survivors of the typically Jurassic and Cretaceous 

 mammals of the order Multituberculata- — diminutive creatures, with 

 jaws approaching those of the rodents in pattern, and with the 

 crowns of the molar teeth bearing numerous tubercles for crushing. 

 These mammals are now generally supposed to have had the same 

 lowly organisation as OimithGrhynchus and Echidna; and if so they were 

 the last survivors of the Monotremata outside the Australian region. 

 The greater part of the Puerco and Cernaysian fauna, however, con- 

 sists of small mammals with a diminutive smooth brain, which 

 might have served very well for the ancestors not only of the 

 modern placental mammals, but also of the lowly pouched mammals, 

 or marsupials, now characteristic of the Austi'alian region, and also 

 met with in tropical America. Some of these ancestral types exhibit 

 teeth and other features very suggestive of the lemurs, and might 

 easily have been modified into the latter ; others look a little like 

 ancestral rodents ; others are clearly at the base of the insectivor- 

 ous and jlesh-eating mammals of the orders Insectivora, Chiroptera, 

 and Carnivora ; while a large number are the little modified fore- 

 runners of the hoofed animals. 



Eocene 



The next early Tertiary mammal fauna, characteristic of the 

 Lower Eocene period, is also nearly identical in Europe and North 

 America. In England it has been found in the Thanet Sands, 

 London Clay, and Woolwich and Reading Beds. In North America 

 it occurs in lake-deposits termed the Wasatch Formation. A few 

 diminutive typical marsupials, apparently almost identical with the 

 opossums which still live in the forests of tropical America, occur 

 in this fauna on both sides of the Atlantic. The ancestral hoofed 

 animals, or Condylarthra, are now more varied and attain larger 

 dimensions than they did previously ; and some of them seem 

 to have already evolved into odd-toed (perissodactyle) and even- 

 toed (artiodactyle) members of the order. There are thus recog- 

 nisable ancestors of the horses and the pigs. The most charac- 

 teristic feature of this fauna, however, is the rise of a tribe of stout 

 animals about as large as tapirs, with five short stumpy toes on 

 remarkably small feet, hence named Amblypoda or Amblydactyla. 

 Corypliodon represents this tribe both in Europe and North America. 



