250 AMPHIBIOUS SAURIANS. 
vived all these changes and revolutions, and still 
retain the leading features under which they first 
appeared upon our planet. 
If we look to the state of the earth, and the 
character of its population, at the time when 
Crocodilean forms were first added to the num- 
ber of its inhabitants, we find that the highest 
class of living beings were reptiles, and that 
the only other vertebrated animals which then 
existed were fishes ; the carnivorous reptiles at 
this early period must therefore have fed chiefly 
upon them, and if in the existing family of 
Crocodiles there be any, that are in a peculiar 
degree piscivorous, their form is that we should 
expect to find in those most ancient fossil genera, 
whose chief supply of food must have been de- 
rived from fishes. 
In the living sub-genera of the Crocodilean 
family, we see the elongated and slender beak 
of the Gavial of the Ganges, constructed to feed 
on fishes; whilst the shorter and stronger snout 
of the broad-nosed Crocodiles and Alligators 
gives them the power of seizing and devouring 
quadrupeds, that come to the banks of rivers 
in hot countries to drink. As there were scarcely 
any mammalia* during the secondary periods, 
whilst the waters were abundantly stored with 
* The small Opossums in the oolite formation at Stonesfield, 
near Oxford, are the only land mammalia whose bones have 
been yet discovered in any strata more ancient than the tertiary. 
