138 
ORIGIN OF LIFE IN AMERICA 
Their earliest centre of distribution lay in what has been 
called Sonoraland, or south-western North America, and 
from here the species have spread in Miocene times, according 
to Dr. Gadow, to the eastern States, to the island of Haiti 
and even to Peru. The latter occurrence is of particular 
importance, as we shall see later on, when we come to the 
consideration of the points of resemblance between the 
Mexican and the South American faunas. Still more remark¬ 
able is the fact that a single species of Spelerpes (S. fuscus) is 
known from some of the remaining fragments of the ancient 
Tyrrhenian continent in southern Europe (see Fig. 8). Even 
Dr. Gadow,* who shows little inclination for reconstructing 
ancient land bridges, does not suggest that this salamander 
could have crossed the Atlantic Ocean without their 
assistance. He thinks a land connection joining north¬ 
eastern North America with north-western Europe, by way 
of Greenland, might have enabled the south European 
Spelerpes to cross from the New World to the Old. 
I concur with Dr. Gadow in the belief of the former 
existence of a land bridge in the extreme North Atlantic, 
but I am of the opinion that it had not yet made its appear¬ 
ance at the time when Spelerpes undertook its journey to 
Europe. 
This short review of some of the characteristic north¬ 
eastern reptiles and amphibians lias clearly revealed a 
relationship of some of the older forms with those of southern 
and eastern Asia and also of southern Europe. In several 
instances it was demonstrated that the eastern States were 
not the original home of the genera, but that the North 
American centre of distribution lay in the south-west. Hence 
it seems possible that the south-west was in remote times, say 
about the commencement of the Tertiary Era, the great centre 
from which reptiles and amphibians wandered eastward. 
Owing to subsequent changes in the climatic conditions of 
the south-west, some genera, and even families, probably 
became extinct there, thus obscuring the original relation¬ 
ship of that part of North America with Asia and Europe. 
Without fossil evidence to guide us, it would seem as if these 
* Gadow, H., “ Mexican Amphibians and Reptiles,” p. 244. 
