AMERICAN RUMINANT-LIKE MAMMALS. 26 1 



Another case of similar kind, and perhaps even more re- 

 markable, has been brought to light by Ameghino. Until the 

 junction of the two Americas, which was effected at the close 

 of the Miocene, the southern continent was an extremely- 

 isolated region and had an altogether peculiar fauna, which 

 differs from that of the northern hemisphere not merely in the 

 genera and families of its mammals, but in their orders. So 

 far as I am at present able to judge, the only mammalian order 

 common to North and South America in the late Oligocene or 

 early Miocene is the Rodentia. Among the peculiar Patago- 

 nian mammals is one which, upon a superficial examination, 

 seems to be an undoubted horse. The aspect of the teeth, 

 skull, trunk, and limb-bones is strikingly equine, and of the 

 feet even more so ; the feet are functionally monodactyl, a 

 large median toe bearing almost the entire weight, and two 

 much reduced lateral toes forming dew-claws, quite as in Proto- 

 hippits or Hipparioii. Yet, when we come to make any careful 

 examination of this skeleton, we soon learn that not only is it not 

 a horse, but that it is not even a perissodactyl. It forms a most 

 interesting and striking example of convergent development. 



Between the Tylopoda and the Pecora we may observe 

 another example of curiously complete parallelism. In this 

 case we see how the former group firmly established them- 

 selves in North America at a time when communication with 

 the Old World had, by some means, been rendered difficult, 

 and how they ramified in many directions, taking here the 

 roles which in the eastern hemisphere were filled by the Pecora 

 and Tragulina. In adapting themselves to these various parts 

 they came to resemble the Eurasian groups in many important 

 respects, but if we attempt to interpret these resemblances as 

 having arisen from relationship and genetic affinity, we are at 

 once landed in hopeless confusion. The conception of the 

 indigenous American selenodont fauna as composing one diver- 

 sified suborder removes these difficulties and marshals the 

 families and genera in orderly array, but it involves such a 

 degree of parallelism in development as may stagger the belief 

 of those who have not made themselves familiar with the 

 actual steps of descent in the mammalian phyla. 



