2 THE MERYCOIDODONTID/E 



from east to west, beginning in the upper Oligocene or earlier. In other words, I believe it possible 

 that the family spread westward and eastward from Wyoming and perhaps from the Saskatchewan 

 area as well. It is certain that we have members of no less than five genera living contemporane- 

 ously in both the eastern and western sections of their known habitat. Stock has collected specimens 

 of at least three genera in southern California in Oligocene-Miocene strata, and I am confident that 

 more will be found there. 



From its humble beginning in the late Eocene, this family spread over an immense territory 

 and reached its culmination in point of numbers of individuals in the Oligocene, whereas the Miocene 

 witnessed the maximum diversity of generic differentiation. Long before the end of the latter epoch 

 there had been developed four distinct lines of descent, while at the same time we see foreshadowed 

 the terminal forms of this great and flourishing family. In the early Pliocene there were some sur- 

 vivors, but before the end of the middle Pliocene they had run their course and vanished completely 

 from the face of the earth. 



Doctor Joseph Leidy and Professor E. D. Cope of Philadelphia, together with Professor O. C. 

 Marsh of Yale, formed the great triumvirate of American vertebrate paleontologists of the last cen- 

 tury. These three described many species of merycoidodonts, and they have been followed by a host 

 of American and many European paleontologists who have published on this family, until the bibliog- 

 raphy comprises nearly four hundred publications. More recent studies have been made by Pro- 

 fessor W. B. Scott, the late Doctor W. D. Matthew, Professor F. B. Loomis, the late Mr. Earl 

 Douglass, and the late Mr. O. A. Peterson, all of whom have made many valuable contributions 

 to our knowledge of this great group. 



Doctor Leidy described and figured the first specimen of the merycoidodonts in 1848, designat- 

 ing it as Merycoidodon culbertsonii-, the generic name meaning ruminant + form -f- tooth (i.e., 

 teeth after the ruminant pattern or selenodont). The specific name was given in honor of Alexander 

 and Thaddeus Culbertson, who collected not only the first specimen of this family but also a great 

 quantity of other fossil material which they sent to the Smithsonian and to other institutions for 

 preservation and study. Doctor Leidy designated these animals "ruminating hogs," and this concept 

 has clung to them ever since. 



Since 1848 more and more material has been collected, so that to date 34 genera (including 

 subgenera) and 129 species and subspecies have been described. 



The greater proportion of evolutionary changes took place in the skull, producing dolichoce- 

 phalic, mesocephalic, and brachycephalic types, up to 0.50, 0.50-0.65, and above 0.65 respectively, 

 the indices being derived by dividing the maximum breadth of the skull by the maximum length. 

 In some of the early genera the orbit was open posteriorly and the auditory bullae were small ; later 

 the orbits closed and inflated bullae became the normal character. In the course of evolution there 

 developed genera with low, flat skulls ; facial and frontal vacuities were formed; in at least one 

 genus a proboscis was probably developed; and the crown pattern of the premolars changed, while 

 hypsodonty was brought about in the molars. 



The skeleton shows far fewer evolutionary changes, although there are distinctions between 

 the various genera. 



I am deeply in debt to members of various museums for favors too numerous to mention, 

 except collectively. These favors consist of the loan of material, including some types; of oppor- 

 tunity for the study of specimens and of the furnishing of photographs and drawings of type and 

 other material; of checking of catalogue data; and of conferences, criticism, and advice extending 

 over a period of several years during which I have been engaged intermittently in the study of this 

 group. 



The following have been of the utmost assistance: Doctor Walter Granger, the late Doctor 

 W. D. Matthew, Mr. Childs Frick, and Mrs. Rachel H. Nichols, at the American Museum of 

 Natural History; Professor F. B. Loomis, Amherst College; Mr. E. B. Howard, Academy of 

 Natural Sciences, Philadelphia; Dr. Chester Stock and Mr. J. L. Ridgway, California Institute of 

 Technology; Dr. A. Avinoff, the late Messrs. Earl Douglass and O. A. Peterson, and Messrs. J. J. 

 Burke and J. L. Kay, Carnegie Museum; Mr. E. S. Riggs, Field Museum; Dr. Thomas Barbour, 



