158 SYSTEMATIC PALEONTOLOGY 



Until the acquisition of fairly complete specimens by the American 

 Museum of Natural History, from which important information has 

 been obtained regarding the shape of the jaws, it was a difficult matter to 

 assign good differential characters to the three species of true elephants 

 found in the United States, for while typical teeth of all three are readily 

 distinguishable, yet intermediate forms of teeth occur which cannot with 

 certainty be distinguished from one another. This is particularly true 

 of the two larger species, Elephas columbi and Elephas imperator, as a 

 small female tooth of the latter very closely resembles a large tooth of 

 Elephas columbi. For this reason the three species of Elephas at present 

 known or recognized from North America have been variously admitted 

 or rejected as valid species, all having been at one time included under 

 Elephas primigenius. Falconer recognized the specific distinctness of 

 Elephas columbi as early as 1857, but for a long time stood alone in this 

 respect, and after Leidy had described Elephas imperator he reconsidered 

 and called the type specimen americanus or columbi. 2 Cope also, though 

 recognizing differences between teeth from various localities and possess- 

 ing jaws of Elephas columbi ( ?) wrote : " It is not clear that the two 

 American forms can as yet be distinguished from the Elephas primi- 

 genius, or from each other, except as probable sub-species, Elephas primi- 

 genius columbi and Elephas primigenius americanus. But more perfect 

 material than we now possess may enable us to distinguish one or both 

 of these more satisfactorily." In writing thus, Cope confused Elephas 

 imperator with Elephas columbi and considered the eastern form of 

 Elephas columbi as distinct from the western, which it may yet prove to 

 be. More important misconceptions were ascribing the bones found in 

 Mexico to the Northern mammoth and in considering this as the original 

 species from which the others had been derived, when all indications 

 point to the southern species as being earlier in point of time. 



This, of course, leaves the problem of the origin of these species un- 

 settled, but we are equally in the dark regarding the derivation of Ameri- 

 can mastodons, for while Cope recorded Mammut proavus from the Loup 



2 The application of Elephas americanus to the mastodon of course pre- 

 cludes its use for any true elephants. 



