180 ORIGIN OF LIFE IN AMEEICA 



Grande. Only one other species of alligator is knoiwn, viz., 

 Alligator sinensis from the Yajigtse Eiver in China.* This 

 enormously discontinuous range is significant, and implies 

 great antiquity. Fortunately we 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 nather 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. Henoe 

 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. 



An 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 Bra, and it seems surprising that they have not 



* Barbour, Th., " Chinese Alligator." 



