TIIK MA^OIALIA OF THE UINTA FORMATrON. 531 



Part IY. 



I?Y HENRY FAIRFIELD OSBORN. 



THE EVOLUTION OP THE UNGULATE FOOT. 



Ill the Uinta and undeilying Washakie beds we meet with, at least, five distinct 

 series of Perissodactyhi, representing the recent Tapiridai and Equidje, also the 

 Titanotheriidtii and Hyracodontidi^, which became extinct in the Miocene, and Amyiio- 

 dontidte which may have given off the true rhinoceros line. The foot bones of each 

 of the series are fortunately represented wholly or in part in the Princeton collection 

 and present interesting transitions to the Bridger types of feet on the one side and the 

 White River on the other. Many notes upon the latter have been derived from the 

 study of the collection in the Museum of Comjiarative Zoology through the courtesy 

 of Prof. Agassiz. The writer is also greatly indebted to Prof. Cope for free access 

 to his collection which is so rich in Lower Eocene forms. 



A careful comparison of these earlier and later forms showed it to be i)ossible to 

 distinguish, in nearly every instance, the separate elements of the feet in each seiies 

 by a number of inconspicuous but thoroughly diagnostic marks. This led the writer 

 to a study of the minor characteristics of the foot bones in the recent and extinct 

 Perissodactyla and the earlier Ungulata in geueial. Kovvalevsky has given us a 

 model for such research in iiis Anchitherium memoir, in which structural modidcation 

 is constantly viewed from the functional standpoint, while we are greatly indebted to 

 Cope for his numerous essays upon the broad lines and philosophy of the transitions 

 from the taxeopod to the recent ungulate foot. The purpose of the present contribu- 

 tion is to indicate the chief characteristics of the foot bones in each of the phyla 

 diverging from the primitive Taxeopoda, chielly in their bearing upon phylogenelic 

 questions and the laws of modification of foot structure. The subjects may be con- 

 veniently treated in the following order: 



I. The foot stnicture in the ancestral Taxeopoda or Protungulata and tin- niodili- 

 cations which take place in the ungulates in general in the evolution from the 

 primitive type. 



