156 OSBORX — THE EVOLUTIOX OF THE HORSE. [April 7, 



RECENT ADVANCES IN OUR KNOWLEDGE OF THE 

 EVOLUTION OF THE HORSE. 



BY HENRY F. OSBORN. 

 {Read April 7, 1904.) 



The American Museum explorations for the development of the 

 horse practically began in 1901 with the first expedition to the 

 Rocky Mountain region in that year, conducted by Dr. J. L. 

 Wortman. By continued exploration and the acquisition of the 

 Cope Collection of fossil vertebrates remains of a large number 

 of fossil horses were secured. In 1901, however, explorations were 

 organized with the particular purpose of securing materials for the 

 further study of the evolution of the horse with the fund donated 

 by the late William C. Whitney. Mr. J. W. Gidley, a graduate of 

 Princeton University, was placed in charge of expeditions sent into 

 Texas, Colorado, South Dakota and Nebraska. The remains of 

 146 horses v/ere secured, making a total of remains representing 

 this animal in the Museum of upwards of 770. 



In the year 1900 the chief discovery was a herd of six Pleistocene 

 horses belonging to the new species Equus scotit, giving us for the 

 first time a complete knowledge of the osteology of the American 

 Pleistocene horse — a large-headed, short-limbed animal, propor- 

 tioned somewhat like the zebra. In 1901, the first year of the 

 Whitney expeditions, Hypohippus was discovered in the Upper 

 IVfiocene, a genus named by Joseph Leidy but hitherto little under- 

 stood ; this animal, although contemporaneous with several highly 

 specialized types of horses, was found to represent a forest-living 

 type, with short crowned teeth and persistent lateral toes. In 

 1902 the remarkable discovery was made of a new genus and 

 species of horse, NeohippaiHon whitneyt, in the Upper Miocene of 

 western Nebraska. This animal, in contrast with the foregoing, 

 was extremely light limbed, proportioned rather like the deer, with 

 diminutive lateral toes, long crowned teeth, and represented a 

 highly specialized, cursorial type, remotely related to the Hippar- 

 ion of Europe. 



Our explorations therefore have demonstrated the existence of 

 two and probably three collateral lines of horses contemporaneous 

 with the Pi-otohippus line, which apparently led into the true 

 horse. The early conclusions of Joseph Leidy, based on far less 



