14G 
ORIGIN OF LIFE IN AMERICA 
America from Asia in pre-Glacial times. Long before the 
advent of the European conquerors in the New World, herds 
of another large ungulate, the horse, roamed about these same 
prairies and no doubt shared the abundant fodder with the 
bison. When the Spaniards landed in America in 1521 it was 
already extinct, and the natives had not any knowledge even of 
the former existence of the horse in their continent. Yet even 
in Pleistocene times several different kinds of wild horses 
still lived in North America and were probably contem¬ 
poraneous with early man. One of these (Equus giganteus) 
seems to liave exceeded in size any known race of horse either 
living or extinct.* What caused the sudden extinction of the 
wild horse all over America we do not know. Professor 
Osbornf suggests that a disease of the nature of the African 
“ rinderpest ” might have done it. The “ tse-tse fly ” renders 
thousands of square miles of Africa uninhabitable for horses, 
and the invasion of a similar pest into America might pos¬ 
sibly have swept away the whole of the equine stock in a short 
time. But the interest aroused among zoologists by the dis¬ 
covery of fossil horses in America was not only connected with 
their unexplained disappearance in modern times, it yielded 
what was thought to be absolutely demonstrative evidence of 
the theory of evolution. Fossil forms no doubt had already 
been discovered in Europe which seemed to indicate that 
the remote ancestors of the existing horse had five digits on 
every foot while intermediate stages with three fully deve¬ 
loped toes were known. In America, horses, or at any rate 
animals possessing all the essential characters of a horse, 
have been brought to light from very early Tertiary deposits, 
possessing four toes and a rudimentary fifth on the hind foot 
and short-crowned teeth. These are succeeded in Oligoceno 
and Miocene strata by others with three toes and short- 
crowned teeth. In still more recent deposits, horses occur 
with three toes and long-crowned teeth which are finally 
followed by horses of the modern type with one toe and long- 
crowned teeth. 
* Gidley, J. W., “ Revision of North American Species of Equus,” 
p. 137. 
t Osborn, H. F., “ Causes of Extinction of Mammalia,” p. S35. 
