PREFACE 



One afternoon in June, 1876, three Princeton undergraduates 

 were lying under the trees on the canal bank, making a languid 

 pretence of preparing for an examination. Suddenly, one of the 

 trio remarked : " I have been reading an old magazine article 

 which describes a fossil-collecting expedition in the West ; why 

 can't we get up something of the kind? " The others replied, as 

 with one voice, " We can ; let's do it." This seemingly idle talk 

 was, for Osborn and myself, a momentous one, for it completely 

 changed the careers which, as we then believed, had been mapped 

 out for us. The random suggestion led directly to the first of the 

 Princeton palseontological expeditions, that of 1877, which took 

 us to the " Bad Lands " of the Bridger region in southwestern 

 Wyoming. The fascination of discovering and exhuming with 

 our own hands the remains of the curious creatures which once 

 inhabited North America, but became extinct ages ago, has proved 

 an enduring delight. It was the wish to extend something of 

 this fascinating interest to a wider circle, that occasioned the 

 preparation of this book. 



The western portion of North America has preserved a marvel- 

 lous series of records of the successive assemblages of animals 

 which once dwelt in this continent, and in southernmost South 

 America an almost equally complete record was made of the 

 strange animals of that region. For the last half-century, or 

 more, many workers haye cooperated to bring this long-vanished 

 world to light and to decipher and interpret the wonderful story 

 of mammalian development in the western hemisphere. The task 

 of making this history intelligible, not to say interesting, to the 

 layman, has been one of formidable difficulty, for it is recorded 

 in the successive modifications of the bones and teeth, and without 

 some knowledge of osteology, these records are in an unknown 



