EVIDENCE FROM PALEONTOLOGY 109 



pletely known than that of the horses and which 

 illustrate similar principles. In several instances we 

 are embarrassed with riches, finding it difficult, or 

 even impracticable, to select from the many possi- 

 bilities the forms which are actually and properly 

 referable to a given series. Indeed, there is every 

 reason to believe that, did we possess well-preserved 

 specimens of every mammal that ever lived on the 

 earth, we should be entirely unable to find a clue that 

 would guide us through the complex maze. 



A family that has been traced from the Pleistocene 

 to the Eocene of North America is that of the tapirs, 

 but, for the most part, by the aid of rare, fragmentary 

 and therefore unsatisfactory materials. This, how- 

 ever, is of less consequence in the case of the tapirs, 

 for they are a very conservative family and have 

 undergone relatively little change. There has been a 

 moderate increase in size and bulk in the successive 

 stages, a few changes in the teeth and skull may be 

 noted, especially the modifications of the latter 

 caused by the development of a proboscis, but other- 

 wise the bony structure of an Eocene tapir differs but 

 little from that of its modern descendants. In the 

 Pleistocene, tapirs extended from Pennsylvania to 

 Argentina and to eastern and southern Asia, but 

 they had vanished from Europe, where they had lived 

 in the Miocene and Pliocene. Thus, at one time or 

 another, they ranged all over the northern hemi- 

 sphere; the significance of this fact will appear in the 

 next lecture. 



