OROHIPPUS 



MESOHIPPUS 



A NEW SPECIMEN OF THE FOUR TOED HORSE 



KAKLIK8T KNOWN ANC'ESTOU OF THK MoDKKN IIOHSK, TIIK SMALL FOIK- 

 TOKl) l-'dllll'ITS, DIfSCOVF.UKI) IN TIIF HAD LANDS OV WYOMING 



7)'// ]\'(ilfi'r (IniiKjcr 



THE continent of Xortli Amci-ica has produced the most complete 

 and best preserved fossil remains of the horse; and it chances that 

 of all institutions, the American Museum possesses the finest col- 

 lection of fossil horses. Aside from fragmentary material, there are eight 

 mounted skeletons in the Hall of Fossils, covering a remarkable series of 

 connecting links from the little four-toed Eohippus of the early Eocene to 

 the large, modernized, one-toed Equus of the Pleistocene or (ilacial PcM-iod, 

 at which time the horse became extinct in North America. 



The skeleton of Eohippus at present mounted in the Museum is of the 

 most ad\anced species of that genus and is from the ^Yind River formation 

 of Wyoming. It was of especial interest therefore, when the expedition 

 of the Department of Vertebrate Palneontology sent to Wyoming the past 

 siiniiiier, discoNcred a nearly coiiiplete skeleton of one of the most primi- 

 ti\e species of Eohippus, prexiously known to science merely by fragments 

 of jaws containing the teeth. This was found in the extreme northwestern 

 corner of Wyoming, in the Wasatch formation of the Big Horn Basin. 



After the close of the great Age of Reptiles, at a time roughly estimated 

 at 3,0()0,()()() years ago when the region was at si-a le\'el, there occurred 

 an uplifting of nionntain I'nnges and a general elexation of the country. 

 The Big Horn Basin was one of sexcral formed by this raising of mountain 

 chains, and into the basin ran the sediment washed from the rocks of the 

 higher surrounding regions. Here in a moist, wai-ni climate and j)robably 

 with an abundance of \egetation, many primitive mammals including the 

 little Eohippus lived and died, and their boiu-s became buried in the slowly 

 accumulating clays and sands, and eventually ix'trificd. .\p])r()\iinately 

 these conditions existed until there had been deposited in this Basin a great 

 mass of sediment 2,()()0 feet thick; the Basin was nearly filled and a drain- 



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