180 
ORIGIN OF LIFE IN AMERICA 
Grande. Only one other species of alligator is known, viz., 
Alligator sinensis from the Yangtse River in China.* This 
enormously discontinuous range is significant, and implies 
great antiquity. Fortunately w r e possess most valuable 
palaeontological evidence as to the alligator’s antecedents. 
Even the most pronounced advocate of accidental dispersal 
would not venture to apply the usual methods of wind, waves 
or hurricanes to explain the origin of this example of dis¬ 
tribution. The generally accepted theory, I believe, is that 
some ancestor of the American alligator has travelled north¬ 
ward, and succeeded in crossing the former land bridge across 
Bering Strait to north-eastern Asia, thence wandering south¬ 
ward to China. We possess no fossil evidence for such a 
belief. All we know is that the rather generalised alligator 
Diplocynodon lived already at the very commencement 
of the Tertiary Era both in North America and in Europe, 
and that it persisted in Europe until Miocene times. Hence 
it seems likely that the modern genus Alligator originated in 
early Tertiary times either in Europe or North America, and 
spread thence to Asia. That America was probably the centre 
of dispersal is indicated by certain characters the Chinese 
alligator has in common with the South American caimans. 
Am equally remarkable fact of distribution is that the true 
crocodile has succeeded in obtaining a footing on the North 
American continent in one single small area, namely, in that 
in which I have already signalled so many tropical species, 
in southern Florida. We are apt to associate crocodiles with 
Africa. Yet they have a much wider distribution. The genus 
Crocodilus occurs in Africa, Syria, India and eastward as far 
as northern Australia. Westward it reappears in South 
America, the West Indies and Central America. The species 
alluded to (Crocodilus americanus) is the only member of the 
family inhabiting the West Indian islands, and it also occurs 
in Central America, Columbia, Ecuador and Venezuela. 
Remains of crocodiles found in the Eocene of Wyoming 
and the eastern States have been referred by Leidy, Cope 
and others to the genus Crocodilus. The presence of croco¬ 
diles in America dates back, then, to the very beginning of 
the Tertiary Era, and it seems surprising that they have not 
* Barbour, Th., “ Chinese Alligator.” 
