LIFE IN TERTIARY TIMES 309 



like the Greenland whale, which no longer had teeth but 

 horny baleen plates. We know that while Porpoises and the 

 Grampus live on fish, Dolphins, Sperm-whales, and Hyperoodon 

 live chiefly on soft cuttle-fish, and Baleen-whales on all kinds 

 of small creatures. Such diet, giving the teeth no work, 

 would account for their disappearance, since there would be 

 no stimulation of the formative bulb. 



A number of works, pre-eminent among which are those 

 of the American palaeontologist, H. F. Osborn (xc, xci, and 

 xcii), have made us remarkably well acquainted with the fauna 

 whose remains were carried down by large rivers during the 

 Eocene Period and deposited in the valleys of the Rocky 

 Mountains. The deposits thus formed are of different ages, 

 and Osborn divides them into four successive groups ; in the 

 first, comprising the deposits of Puerco and Torrejon in the basin 

 of the San Juan of New Mexico, 1 were found Neoplagiaulax and 

 Polytnastodon, inherited from the Triassic period, Insectivora, 2 

 Creodonta, Taeniodontia, Condylarthra, and Amblypoda. 

 Some of the animals of this first phase have also been found 

 in France, 3 others in Patagonia. 4 From the second phase 

 onward, at Wasatch, there are added to these primitive groups 

 Rodents, genuine Perissodactyla, and already — interesting 

 to observe — Primates. 



During this second phase there are no longer any forms 

 common to both North and South America, which were at that 

 time probably separated, but numerous species appear in 

 Europe. They become rare during the third phase, which 

 corresponds to the whole of the Meso-Nummulitic, 5 a period 

 that witnessed the disappearance of the Condylarthra and the 

 appearance of families indigenous to the New World, to which 

 they are restricted, such as the Oreodontidae, herbivorous 

 animals with an even number of digits, which lasted until the 

 end of the Tertiary, and the Titanotheridae, represented by 

 the gigantic Titanotherium or Brontotherium. Huge monsters 

 were also produced among the Amblypoda. 



1 These deposits are of the Eonummulitic Epoch (Montian, Thanetian, 

 Londinian). 



2 Miochlosnus, Oxyacodus, Wortmannia, Onyckodecles, Triiosodon, 

 Oxyclcenus, Loxolophus. 



3 They belong to the fauna of Torrejon : Neoplagiaulax, Proviverridae, 

 Arctocyonidae, Mesonychidae, Phenacodus. 



* Trigonolestes, Helohyus, Parahyus. 

 8 Fauna of Puerco. 



