460 H. F. Osborn — Mammalia in North A me? 



ica. 



... -| Titanotheres. Upon one side the Titanotheres present 



j Horses. the buno-selenodont extreme with most 



\ Pateotheres. analogies to the Artiodactyla in tooth struc- 

 [ Tapirs. ture and in their truly Artiodactyl fore 



' * • fe^ feet and bony horns. (If, as Cope sup- 

 ( Hyracodonts. P oses > tne piplarthra form a natural group, 

 ....•] Amynodonts! some Perissodactyls should certainly be 

 ( Rhinoceroses, more Artiodactyl than others.) The 

 Horses and Palseotheres diverge from the buno-selenodont type 

 towards the Lophodont ; they were early separated in foot 

 structure. The Tapirs, Lophiodonts, and BLelaletes show well- 

 marked transverse crests and incipient external crests. This 

 brings us to the other Lophodont extreme, the Rhinoceros-like 

 forms, with complete transverse and external crests. There 

 are many other minor characters which support this as the 

 natural arrangement of the Perissodactyls. I think it can be 

 shown conclusively that these eight or nine series diverged 

 from each other before the Wahsatch, and that all attempts 

 to derive them from each other in later periods will break 

 down. They will be found to converge into the unknown Sub- 

 Wahsatch period, to stem forms as indicated by the brackets. 



The Titanotheres have been traced by Cope back to Lamb- 

 dotherium in the Wahsatch ; in the Wind River the true 

 Palseosyops is found, and in the Bridger this becomes the pre- 

 dominant perissodactyl family, and spreads out into a great 

 variety of forms, which have recently been carefully described 

 by Earle. In the Washakie there are some still larger forms, 

 and Marsh has traced the line through the teeth of Diplacodon 

 of the Uinta to the true Titanotheres. Still the origin of the 

 flattened skull and remarkable anterior pair of horns has never 

 been known; Hatcher reports species with very small horns in 

 the base of the Titanotherium beds (Lower Miocene). Wort- 

 man has just reported to me the brilliant discovery of an upper 

 Eocene (Bridger and Washakie) Palseosyops with a flattened 

 skull and rudimentary horns just appearing upon the nasals ! 

 This forms the desired connecting link. 



The early history of the horses, probably starting with the 

 Puerco Condylarth Euprotogonia, and passing through Hyraco- 

 therium, Pachynolophus, Epihippus, Mesohippus, is now 

 familiar enough. It is the later history which requires eluci- 

 dation, and is producing the most unexpected number of paral- 

 lel lines of horses, out of one of which only our modern horse 

 sprang. Here we are especially indebted to Cope, Pavlow, 

 and Scott. By general consent Hipparion comes out of its 

 old position in the true line as displaying the most extreme 



