MERISTIC VARIATION 59 



horselike animals and regarded as ancestors of the modern horse, 

 had each three toes that probably reached very near the ground. 



Passing still further back (clown) in geologic time and looking 

 for a still more remote ancestor, we get beyond what can be 

 called a true horse, as can the protohippus and the hipparion. 

 But yet there is among these long-extinct forms sufficient horse- 

 like character to suggest ancestry, as with the forest horse and 

 desert horse of the Whitney find in Wyoming, forty inches high 

 and three toes down. 1 As we progress in this direction, however, 

 the toes increase in number to four and even five, clearly indi- 

 cating that the modern horse has developed from a five-toed ances- 

 tor like the Eohippus, twelve to sixteen inches high and all toes 

 down, also discovered in Wyoming where it flourished, according 

 to Osborn, some three million years ago or thereabouts. 2 



If we begin with the modern two-toed species and attempt to 

 read their story backwards, we soon land among the same four- 

 or five-toed primitive forms just mentioned, forcing the conclu- 

 sion that the one-toed and the two-toed species of recent times 

 have each descended from five-toed progenitors, indeed, we may 

 even believe from the same five-toed progenitors. 



The manner of this descent is not difficult to trace by the 

 comparison of modern species with similar extinct forms in suc- 

 cessive downward (backward) geologic times. In almost the 

 lowest tertiary rocks of both North America and Europe occur 

 fossil remains of large ungulates. These " Coryphodons " were 

 supplied with five-toed feet much like the elephant of to-day, 

 that has survived by virtue of his teeth and in spite of his feet. 



Ascending to the Miocene Tertiary, we find large ungulates 

 still remaining, but digit I is gone, while the metacarpal (or meta- 

 tarsal) has become much lengthened and the third and fourth 

 members greatly strengthened, not only in their own development 



1 Henry F. Osborn, Origin and History of the Horse. 



2 The development of the horse from an ancestor only twelve to sixteen inches 

 high and with five toes, all down, is the best instance of progressive evolution 

 of which we have any knowledge. Doubtless the evolution of other species has 

 been no less extended and fascinating, but of no other case do we possess so 

 complete a history, thanks for which are in large measure due to the generosity 

 of the late William C. Whitney and to the labors of Professor Henry F. Osborn. 

 See also chap, x, sect. ii. 



