20 



i.\/A'A'/r.i.v .\irs/':cM (,rii)i-: Lh:MLh:rs 



Ix'cn ^(M»('iall>- called. l)Ut I lie animal was miicli lai-^c)-. ('(lUallin^ a Slict- 

 land poiiN- in size. A (•()nii)l('t(' skeleton of the 11 ifpolii ppus (shown in 

 wall case) was lound near Pawnee Ruttcs. ( 'oloiado, in MX)) hy Mr. 

 l^arnuni Hrown, of the \\'hiti;ev exi)edition. 



II i/pohippus first aj)j)ears in the Middle Miocene, and sur\ives alon^ 

 witli more advanced stages of the three-toed hoi-ses. It isa lai'^eiandmore 

 heavily j)roi)()rti()ne(l animal; the wide fiat hoofs and strong side toes 

 enal)led it to tread on soft jii-ound. and the teeth are fitted foi- hi-ow.sing 

 rather than jirazin^-. Hence J^rofessor Oshoin considers it as adapted for 

 a foi-est life, and has nanunl it the ''three-toed foi'est horse." The 

 I'estoration illustrates this sui)posed habitat and ada])tation. 



S and 9. Parahippus. Miocene. In Pdrahippas the tooth-erests 

 are somewhat hi<;lier, and the transverse lidges on the uj^j^er molars are 

 beginning;" to change shape so as to become a second pair of crescents 

 inside the outer pair. In the valleys between the cros.s-ci-ests and on the 

 sides and base of the crown, a deposit of cement appeal's on the surface 

 of the enamel. In some species there is a considerable amount, but 

 usually it is a ver}- thin coat. There is no cement on the milk teeth. The 

 feet show a decided advance over the preceding stages, the side toes 

 are very slender, and no longer touch the ground. The fifth digit of the 

 fore foot is in some species a very short small splint, in others it is still 

 further reduced to a little irregular nodule of ])one. This stage first 

 appears in the Lower Miocene, and several skulls and incomplete skele- 

 tons have recently been obtained from formations of this age. It sur- 

 vived however, although rare, as a contemporar}- of the later three-toed 



horses. 



10. Merychippus. Middle 

 Miocene. This stage marks 

 the transition between the older 

 .short-crowned teeth without ce- 

 ment, and the long-crowned 

 heavily cemented teeth of the 

 later stages. The permanent 

 molars are intei'mediate in length 

 of crown, and quite heavily ce- 

 nuMited. but the milk molars are 

 shoi't-crowniMl and have little or 

 no cement; they are not easily distinguishabh^Vom th(^se of /^f//-a/?/pp?KS'. 

 The side toc^s are slender and no longer reach the giound: in some species 

 they are almost reduced to sj)lints. Merychippus is common in the 

 ^Middle and later Miocene, and many skulls, jaws and incomplete skele- 

 tons are contaiiUMJ in our collections, some of which aic^ i)laced on exhibi- 



Fig. 10. Parahippus. Lower Miocene. 

 Upper teeth, one-half natural size. Short- 

 crowned teeth, traces of cement. The 

 teeth are larger than in Mesohippus [the 

 drawing is on a smaller scalel, the crowns 

 a little longer, and the inner "crests" 

 begin to .«;how the chungo to "crescents" 



J 



