134 ORIGIN OF LIFE IN AMERICA 



Besides these so-called fresh-water turtles, we have in 

 America even terrestrial ones. The box-turtles (Terrapene 

 = Cistudo), for instance, are strictly confined to the land, where 

 they live largely on vegetable matter and berries. The six 

 species are distributed from Mexico in the south-west to the 

 New England States in the north-east. In the more northern 

 habitats they burrow to some depth in soft ground and pass 

 the winter there. All the box turtles inhabit North America, 

 the genus Terrapene to which they belong being, in Dr. Hay's 

 opinion, of North American origin. The oldest fossil species 

 (T. putnami) comes from a deposit in Florida stated to be 

 of Pliocene age. Dr. Hay * is inclined to the belief that the 

 genus arose in North America, having probably been derived 

 from Emys. If this should be the case, the origin of Emys 

 itself must have taken place at a much earlier date than the 

 Pliocene. Indeed it is possible that Emys is one of the most 

 ancient of Chelonian genera, for Dr. Boulenger f argued that 

 it is in many respects the least specialized of the Emydidae 

 and that it should be placed at the base of the family. It is 

 of interest to note that although box turtles lived in North 

 America at least since Pliocene times, they have not been 

 able to spread beyond the confines of the continent. This 

 gives us some idea of the slow rate of dispersal of these 

 creatures. 



Of the family of snapping turtles (Chelydridae) a few 

 fossil remains are known from the Jurassic and Cretaceous, 

 though not of existing genera. To judge from their distri- 

 bution the latter must nevertheless be very ancient. These 

 large fresh-water Chelonians with their proportionately huge 

 and sinisters heads, are, according to Dr. Ditmars, bold and 

 aggressive fighters, their massive, keen-edged jaws causing 

 them to be the terror of most of the aquatic and semi -aquatic 

 creatures. There are three species in North America. One 

 of these ranges from Mexico, east of the Bocky Mountains, 

 to Canada, but far to the south of Mexico the same species 

 (Chelydra serpentina) reappears in Ecuador. Such a very 

 peculiar discontinuous range is not unknown among fresh- 



* Hay, 0. P., "Fossil Turtles of North America," p. 360. 

 f Boulenger G. A., " Catalogue of Chelonia," p. 49, 



