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. Boulengerf 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 he 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 Rocky 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, O. P., “Fossil Turtles of North America,” p. 360. 
t Boulenger G. A., “ Catalogue of Ohelonia,” p. 49. 
