THE FORT UNION OF THE CRAZY MOUNTAIN 

 FIELD, MONTANA, AND ITS MAMMALIAN 

 FAUNAS 



By George Gaylord Simpson 



American Museum of Natural History, New York City 



INTRODUCTION 



This work is chiefly devoted to the description and discussion of 

 a large collection of Paleocene mammals, from the Fort Union of 

 central Montana, belonging to the United States National Museum. 

 The first part of the memoir is geological, chiefly stratigraphic and 

 paleontological. The location and general characteristics of the 

 mammal-bearing area are described, followed by a resume of its 

 stratigraphy and geologic ftnicture. The general areal geology is 

 only briefly outhned, and details are largely confined to the beds in 

 which the mammals occur. In the paleontological section, the various 

 fossil localities are hsted, and the mammalian fauna of each is given, 

 together with a summary of all fossil mammals found in the field. 

 Faunal succession and faunal correlation, supplementing the remarks 

 made in the previous section on more purely stratigraphic correlation, 

 are discussed in detail. The general aspect and ecologic relation- 

 ships of the mammaUan faunas are also discussed. Nonmammalian 

 fossils are incidentally mentioned, without any attempt at exhaustive 

 treatment. 



The second and longer part of the memoir is zoological and is 

 devoted to definitions of all taxonomic groups which were originally 

 described from this field or the conception of which is markedly 

 affected by material from here, to discussion of the relationships 

 and phylogeny of the mammals represented, and to description of 

 the specimens in the coUection. 



Geology outside the area of reference and mammals other than 

 those definitely identified here are mentioned only for the sake of 

 comparison. 



In addition to the National Museum collection, specimens from 

 this field now at Princeton University are included. Reference is 

 also made to a small collection in the Carnegie Museum, but since 

 this includes nothing not better represented in the National Museum 

 collection, none of it is treated in detail. Some, but not all, of a 

 large collection in the American Museum of Natural History from 



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