THE MIOCENE OF EUROPE, ASIA, AND NORTH AMERICA 287 



diceratheres. The horses are becoming more varied, including Parahippus 

 {P. nebrascensis) as well as an extremely light-limbed form, possibly similar 

 to the AUippus described by Douglass^ from the Lower IVIiocene Fort 

 Logan Formation of Montana; this is an equine which combines brach- 

 yodont molar teeth with long and very slender limbs and feet. There are 



Porcupine Butte 

 Volcanic ash layer 



Mierycochoerus 

 zone 



Blastomeryx 



Parahippus 



Cynoc/esmus 



Phlaocyon 



Oligubunis 



Megalictis 



Oxydactylus 



Desmathyus 



Protomeryx 



Merycochoerus 



Merychyus (abundant) 



Aelurocyon 



Arctoryctis 



Enioptychus 



Lepus 



Cajc areous_s ha]^ 

 limestone layers 



Promery- 

 cochcems 



Promerycochcerus 

 (very abundant 

 and characteristic) 



Dicer a therium 



Elotherium 



Steneofiber 



/iypertragu/us 



Parahippus (small sp) 



Leptauchenia 

 (near base) 



Nimravus 

 Moropus 

 Dinohyus 

 Mesoreodon 



BRULE ^^^^:^-^^^^^:r^^^^Leptauchenia zone - 



By permission of the U.S. Geological Survey. 

 Fig. 141. — Scale section of the Rosebud Formation. 



After Thomson and Matthew. 



also more diminutive horses, scarcely exceeding in size the Oligocene 

 Mesohippus. All these horses have short-crowned molar teeth. 



Of the rodents all the Oligocene families continue, and Matthew finds 

 evidence of the occurrence of the heteromyids, the leaping rodents related 

 to the existing Heteromys, which is in the same family with the 'American 

 kangaroo rat' or Dipodomys. Especially interesting is the occurrence of 

 a new insectivore, Arctorydes, doubtfully related to the South African 

 chrysochlorids, or Cape Golden moles. 



Of the Carnivora the felids of this stage still await discovery. The 



^ Douglass, E., Fossil Horses from North Dakota and Montana. 

 Vol. IV, nos. 3 and 4, 1908. 



Ann. Carneg. Mus., 



