36 Department of Vertebrate Palceontology. 



28. Ornitholestes hermanni Oshorn. 



Upper Jtirassic (Como), Wyoming. 



This beautiful little skeleton, about seven feet in length, 

 represents a little-known group of Carnivorous Dinosaurs 

 adapted for swift running and the seizing of a light and agile 

 prey. The tail is extremely long, slender, and whip-like, the 

 hind limbs long and the feet like those of a bird, while the 

 small fore limbs are modified into remarkable prehensile 

 organs, the first and second digits greatly elongated and 

 opposed, with large curved claws, the third digit small and 

 slender, and the fourth atrophied. 



OsBORN, Bull. Am. Mus. Nat. Hist., XIX, 1903, pp. 459-464. 



29. Mesohippus bairdi Leidy. 



Middle Oligocene (White River), South Dakota. 



This classic species represents an early stage in the evolu- 

 tion of the Horse. It is smaller than the modern Dorcas 

 Gazelle, and has three toes on each foot, the lateral toes 

 slender but reaching to the ground. Vestiges of the first and 

 fifth digits are still preserved in the fore foot. Mesohippus is 

 somewhat peculiar in the unusual length of the hind limbs as 

 compared with the fore; in other respects it is intermediate 

 between the four-toed horses of the Eocene and the modern 

 horse. 



Scott, W. B., On the Osteology of Mesohippus and Leptomeryx, Jour. 



Morph., V, 1891, pp. 301-406. 

 Farr, Notes on the Osteology of the White River Horses, Proc. Amer. 



Phil. Soc, XXXV, 1896, p. 147-175- 



30. Merycodus osborni Matthew. 



Middle Miocene, Pawnee Creek Bed, Colorado. 



Merycodus is a collateral ancestor of the modem Pronghorn 

 Antelope of Western North America, but is distinguished by 

 large, branching, deciduous antlers like those of the Deer. 



