ORIGIN, RELATIONSHIPS, AND PHYLOGENY 



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structures have nearly the same relative positions in respect to the jaws in all of the genera. The 

 same conditions prevail in the more primitive ruminants. Coupled with these factors is the lack of 

 their remains in river deposits, as mentioned above, and this combination apparently casts grave 

 doubt on the inference that any of the oreodonts were aquatic or amphibious. Cyclopdius, 

 Leptauchenia, and perhaps Merycochaerus are almost the only controversial genera, and the structure 



Fig. 2. — Chart of the phylogeny and geological sequence of the Merycoidodontidx. 



of their skeletons, excluding the skulls for the sake of argument, shows no indication of any 

 amphibious adaptation. By analogy with the recent mammals, the size and the direction of the 

 auditory meatus are correlated with the size and shape of the external ears. 



Relationship of Genera and Polyphyletic Development (Figs. 2-7): As previously 

 stated, Protoreodon is the earliest known genus of this family, but the molars possess a protoconule 

 and the feet are longer than we should expect them to be, if this genus is the direct ancestor of the 

 Oligocene forms. As a consequence I believe it stands a little to one side of the unknown stem 



