112 
ORIGIN OF LIFE IN AMERICA 
as well as the nature of the land bridge which enabled the 
deer to reach western America rather than the east, will be 
discussed in one of the subsequent chapters. Some of the 
more primitive forms still survive in South America, where 
they have now been pressed into the mountain regions. The 
newer and more vigorous types must have passed into North 
America as soon as that continent became definitely connected 
with South America in later Tertiary times. 
In speaking of the western North American fauna, Pro¬ 
fessor Osborn * tells us that in middle Miocene the peculiarly 
American Hypertragulidae disappeared, while the European 
Cervidae and the distinctly American Merycodontinae took 
their place. Professor Osborn alludes no doubt to Palaeo- 
meryx and Blastomeryx which seem to have originated in 
southern Europe, and spread subsequently eastward to India 
and onward to America. Both apparently became extinct in 
North America before the advent of Odocoileus from the 
south. 
The other large hoofed animal I alluded to as frequenting 
the lower slopes of the Rocky Mountains is one of the most 
peculiar creatures in existence. It is so different from other 
animals that it occupies the exclusive position of being the 
solitary member of' a distinct family. Known among zoo¬ 
logists as the “prong-horn” (Antilocapra americana), and 
among hunters as the “ antelope,” this splendid animal 
possesses the gracef ul movements of the latter, while its horns 
have a superficial resemblance to the antlers of a deer. There 
is not the least real likeness, however, between the antlers 
of the prong-liorn and those of a deer, for they are not solid, 
but hollow like the horns of a goat. The horn-sheaths,' 
like the antlers of a deer, are shed and reproduced at regular 
intervals. The prong-horn ranges from eastern Mexico to 
Saskatchewan in Canada and from the Missouri River in the 
east to the Cascade Mountains of Oregon in the west. Hence 
it is now a peculiarly western species, while it had crossed 
the Mississippi during the Pleistocene Period, and roamed 
about Illinois and Wisconsin. The closely-allied extinct 
genus Merycodus (Cosoryx) made its first appearance in the 
Osborn, H. F., “ Cenozoic Mammal Horizons,” p. 77. 
