PREFACE ix 



of evolution; they were omitted in the pioneer work of Leid}', Marsh, and 

 Cope. Tliis precision in America, coupled with the precision especially of 

 Professor Deperet's records and observations in France, has rendered possi- 

 ble the present comparison between the New and Old Worlds. Large 

 collections have been secured also by the museums of Princeton University 

 and the University of California, by the Carnegie Museum of Pittsburgh, 

 the Field Museum of Natural History of Chicago ; and some few additions 

 have been made in recent years to the famous collection brought together 

 by Professor Marsh in Yale University. The equally famous collection of 

 Cope is now the property of the American Museum of Natural History. 



The space and time distribution of the mammal life of Europe as set 

 forth in Deperet's articles in the Comptes rendus, I have brought together 

 in visual form in a new series of maps. 



The American records, sections, and maps are drawn from those brought 

 together in my recent bulletin, ''Cenozoic Mammal Horizons of Western 

 North America," together with some additions from my observations in 

 Africa and from the very latest work in Wyoming. I am here indebted 

 especially to the cooperation of Mr. Granger. The United States Geological 

 Survey has given permission to reproduce many of the illustrations from 

 my bulletin. 



The reader who finds it difficult to picture the rare and ancient forms 

 of mammals has to thank that gifted artist of the life of the extinct world, 

 Mr. Charles R. Knight, for the series of restorations drawn under my 

 personal direction, which are brought together for the first time in this 

 volume. It is always to be understood that such restorations represent 

 hypotheses merely or approximations to the truth. We know little or 

 nothing about the color markings of these extinct forms, and even the 

 attempt to outline the proportions of the limbs and body is somewhat hazard- 

 ous ; yet these representations serve, in connection with photographs of the 

 skeletons, to give us a sense of the general size and proportion, and to 

 assemble before the eye such inferences as to the homes and habits of the 

 animals as can be deduced from their skeletons, especially from the teeth 

 and feet, and from the kind of rock in which their remains have been 

 discovered. 



Mrs. L. M. Sterling has prepared many of the anatomical and geological 

 illustrations with artistic fidelity. Mr. Aleth Biorn and Mrs. IMosenthal 

 have prepared the Deperet series of maps. Mr. Erwin S. Christman has 

 contributed several drawings. The field photographs are chiefly the work 

 of Mr. Albert Thomson and other members of our field parties. The photo- 

 graphs of skeletons are part of the remarkable series executed by Mr. A. E. 

 Anderson. I am indebted to many workers in other institutions for generous 

 assistance. In the palaeobotanic work I have enjoyed the assistance of jVIiss 

 Elsbeth Kroeber, also of Messrs. F. A. Knowlton, A. A. Hollick, and T. D. 

 A. Cockerel!, 



