470 CHARLES C. MOOK 
waters themselves. On land, large and small carnivorous dinosaurs 
roamed about, seeking what they might devour; stegosaurs and 
camptosaurs endeavored to escape their voracious contemporaries; 
some frogs inhabited the swamps. In the rivers and lakes lung 
fish swam about. Fresh-water mollusks and crustaceans lined 
the river and lake bottoms in places or swam about freely in the 
water. Cycads grew in abundance, and soft swamp vegetation 
probably furnished the food supply for hungry reptiles. In some 
such environment as this, or at any rate in one very much like it, 
lived the American sauropod dinosaurs. So far as is indicated 
by evidence now directly available, conditions of practically the 
same sort prevailed in other parts of the world inhabited by 
Sauropoda. 
